BECKHOFF EL7037 User Manual
Documentation
EL70x7
Stepper Motor Terminals, vector control
Version
Date
1.0
11.05.2015
Table of contents
Table of contents
1 Foreword ....................................................................................................................................................5
1.1 Notes on the documentation............................................................................................................. 5
1.2 Safety instructions ............................................................................................................................ 6
1.3 Documentation issue staus............................................................................................................... 7
1.4 Version identification of EtherCAT devices....................................................................................... 8
2 Product overview.....................................................................................................................................12
2.1 EL7037 ........................................................................................................................................... 12
2.1.1 EL7037 - Introduction..........................................................................................................12
2.1.2 EL7037 - Technical data .....................................................................................................14
2.2 EL7047 ........................................................................................................................................... 15
2.2.1 EL7047 - Introduction..........................................................................................................15
2.2.2 EL7047 - Technical data .....................................................................................................17
2.3 Technology ..................................................................................................................................... 18
2.3.1 Stepper motor .....................................................................................................................18
2.3.2 Standard mode ...................................................................................................................22
2.3.3 Field-oriented control ..........................................................................................................23
2.3.4 Sensorless operation ..........................................................................................................25
2.4 Start-up ........................................................................................................................................... 26
3 Basics communication ...........................................................................................................................27
3.1 EtherCAT basics............................................................................................................................. 27
3.2 EtherCAT cabling – wire-bound...................................................................................................... 27
3.3 General notes for setting the watchdog .......................................................................................... 28
3.4 EtherCAT State Machine ................................................................................................................ 30
3.5 CoE Interface.................................................................................................................................. 32
3.6 Distributed Clock............................................................................................................................. 37
4 Installation................................................................................................................................................38
4.1 Installation on mounting rails .......................................................................................................... 38
4.2 Connection system ......................................................................................................................... 41
4.3 Installation position ......................................................................................................................... 45
4.4 Mounting of Passive Terminals....................................................................................................... 46
4.5 Shielding concept ........................................................................................................................... 47
4.6 EL7037 ........................................................................................................................................... 48
4.6.1 EL7037 - LEDs and connection ..........................................................................................48
4.6.2 EL7037 - General connection examples.............................................................................50
4.7 EL7047 ........................................................................................................................................... 53
4.7.1 EL7047 - LEDs and connection ..........................................................................................53
4.7.2 EL7047 - General connection examples.............................................................................55
5 Commissioning........................................................................................................................................58
5.1 TwinCAT 2.1x ................................................................................................................................. 58
5.1.1 Installation of the TwinCAT real-time driver ........................................................................58
5.1.2 Notes regarding ESI device description..............................................................................62
5.1.3 Offline configuration creation (master: TwinCAT 2.x) .........................................................66
5.1.4 Online configuration creation ‘scanning’ (master: TwinCAT 2.x) ........................................72
5.1.5 EtherCAT slave process data settings................................................................................81
5.1.6 Configuration by means of the TwinCAT System Manager ................................................82
5.2 General Notes - EtherCAT Slave Application ................................................................................. 90
5.3 Start-up and parameter configuration ............................................................................................. 99
5.3.1 Process data .......................................................................................................................99
EL70x7 3Version 1.0
Table of contents
5.3.2 Integration into the NC configuration ................................................................................104
5.3.3 Configuring the main parameters - Settings in the CoE register....................................... 109
5.3.4 Configuring the main parameter - Selecting the reference velocity ..................................112
5.3.5 Application example..........................................................................................................117
5.4 Operating modes .......................................................................................................................... 123
5.4.1 Overview ...........................................................................................................................123
5.4.2 Velocity direct....................................................................................................................125
5.4.3 Position controller .............................................................................................................128
5.4.4 Extended Velocity mode ...................................................................................................131
5.4.5 Extended Position mode ...................................................................................................134
5.4.6 Velocity sensorless ..........................................................................................................137
5.4.7 Basic principles: "Positioning interface" ............................................................................140
6 Configuration by means of the TwinCAT System Manager ..............................................................155
6.1 EL7037 ......................................................................................................................................... 155
6.1.1 Object description and parameterization - Profile-specific objects ...................................155
6.1.2 Object description and parameterization - standard objects.............................................166
6.2 EL7047 ......................................................................................................................................... 179
6.2.1 Object description and parameterization - Profile-specific objects ...................................179
6.2.2 Object description and parameterization - standard objects.............................................190
7 Error correction .....................................................................................................................................203
7.1 Diagnosis - Diag Messages .......................................................................................................... 203
8 Appendix ................................................................................................................................................208
8.1 UL notice....................................................................................................................................... 208
8.2 EtherCAT AL Status Codes .......................................................................................................... 210
8.3 Firmware EL/ES/EM/EPxxxx ........................................................................................................ 210
8.4 Firmware compatibility .................................................................................................................. 220
8.5 Restoring the delivery state .......................................................................................................... 220
8.6 Support and Service ..................................................................................................................... 222
EL70x74 Version 1.0
Foreword
1 Foreword
1.1 Notes on the documentation
This description is only intended for the use of trained specialists in control and automation engineering who
are familiar with the applicable national standards.
It is essential that the following notes and explanations are followed when installing and commissioning
these components.
The responsible staff must ensure that the application or use of the products described satisfy all the
requirements for safety, including all the relevant laws, regulations, guidelines and standards.
Disclaimer
The documentation has been prepared with care. The products described are, however, constantly under
development.
For that reason the documentation is not in every case checked for consistency with performance data,
standards or other characteristics.
In the event that it contains technical or editorial errors, we retain the right to make alterations at any time
and without warning.
No claims for the modification of products that have already been supplied may be made on the basis of the
data, diagrams and descriptions in this documentation.
Trademarks
Beckhoff®, TwinCAT®, EtherCAT®, Safety over EtherCAT®, TwinSAFE®, XFC®and XTS® are registered
trademarks of and licensed by Beckhoff Automation GmbH.
Other designations used in this publication may be trademarks whose use by third parties for their own
purposes could violate the rights of the owners.
Patent Pending
The EtherCAT Technology is covered, including but not limited to the following patent applications and
patents:
EP1590927, EP1789857, DE102004044764, DE102007017835
with corresponding applications or registrations in various other countries.
The TwinCAT Technology is covered, including but not limited to the following patent applications and
patents:
EP0851348, US6167425 with corresponding applications or registrations in various other countries.
EtherCAT® is registered trademark and patented technology, licensed by Beckhoff Automation GmbH,
Germany
Copyright
© Beckhoff Automation GmbH & Co. KG, Germany.
The reproduction, distribution and utilization of this document as well as the communication of its contents to
others without express authorization are prohibited.
Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a
patent, utility model or design.
EL70x7 5Version 1.0
Foreword
1.2 Safety instructions
Safety regulations
Please note the following safety instructions and explanations!
Product-specific safety instructions can be found on following pages or in the areas mounting, wiring,
commissioning etc.
Exclusion of liability
All the components are supplied in particular hardware and software configurations appropriate for the
application. Modifications to hardware or software configurations other than those described in the
documentation are not permitted, and nullify the liability of Beckhoff Automation GmbH & Co. KG.
Personnel qualification
This description is only intended for trained specialists in control, automation and drive engineering who are
familiar with the applicable national standards.
Description of symbols
In this documentation the following symbols are used with an accompanying safety instruction or note. The
safety instructions must be read carefully and followed without fail!
Serious risk of injury!
Failure to follow the safety instructions associated with this symbol directly endangers the
DANGER
life and health of persons.
Risk of injury!
Failure to follow the safety instructions associated with this symbol endangers the life and
WARNING
health of persons.
Personal injuries!
Failure to follow the safety instructions associated with this symbol can lead to injuries to
CAUTION
persons.
Damage to the environment or devices
Failure to follow the instructions associated with this symbol can lead to damage to the en-
Attention
vironment or equipment.
Note
Tip or pointer
This symbol indicates information that contributes to better understanding.
EL70x76 Version 1.0
1.3 Documentation issue staus
Version Comment
1.0 - Minor corrections
- Layout adaption
- 1st public issue
0.4 - Minor corrections
- Addenda EL7037
0.3 - Minor corrections
0.2 - Minor corrections
0.1 - Preliminary documentation
Foreword
EL70x7 7Version 1.0
Foreword
1.4 Version identification of EtherCAT devices
Designation
A Beckhoff EtherCAT device has a 14-digit designation, made up of
• family key
• type
• version
• revision
Example Family Type Version Revision
EL3314-0000-0016 EL terminal
(12 mm, nonpluggable
connection level)
CU2008-0000-0000CU device 2008 (8-port fast
ES3602-0010-0017 ES terminal
(12 mm, pluggable
connection level)
3314 (4-channel
thermocouple
terminal)
ethernet switch)
3602 (2-channel
voltage
measurement)
0000 (basic type) 0016
0000 (basic type) 0000
0010 (highprecision version)
0017
Notes
• the elements named above make up the technical designation
• The order designation, conversely, is made up of
- family key (EL, EP, CU, ES, KL, CX, etc.)
- type
- version
• The revision shows the technical progress, such as the extension of features with regard to the
EtherCAT communication, and is managed by Beckhoff.
In principle, a device with a higher revision can replace a device with a lower revision, unless specified
otherwise, e.g. in the documentation.
Associated and synonymous with each revision there is usually a description (ESI, EtherCAT Slave
Information) in the form of an XML file, which is available for download from the Beckhoff website.
The revision has been applied to the IP20 terminals on the outside since 2014/01, see fig. 1.
• The type, version and revision are read as decimal numbers, even if they are technically saved in
hexadecimal.
Identification number
Beckhoff EtherCAT devices from the different lines have different kinds of identification numbers:
Production lot/batch number/serial number/date code/D number
Serial number is the name generally given to the 8-digit number that is printed on the device or attached to it
on a sticker. This serial number indicates the as-built status on delivery and thus ambiguously marks a whole
production lot.
Structure of the serial number: KK YY FF HH
KK - week of production (CW, calendar week)
YY - year of production
FF - firmware version
HH - hardware version
Example with ser. no.: 12063A02: 12 - production week 12 06 - production year 2006 3A - firmware version
3A 02 - hardware version 02
EL70x78 Version 1.0
Foreword
Exceptions can occur in the IP67 area , where the following syntax can be used (see respective device
documentation):
Syntax: D ww yy x y z u
D - prefix designation
ww - calendar week
yy - year
x - firmware version of the bus PCB
y - hardware version of the bus PCB
z - firmware version of the I/O PCB
u - hardware version of the I/O PCB
Example: D.22081501 calendar week 22 of the year 2008 firmware version of bus PCB: 1 hardware version
of bus PCB: 5 firmware version of I/O PCB: 0 (no firmware necessary for this PCB) hardware version of I/O
PCB: 1
Unique serial number/ID
Beyond that there are some series in which each individual module has its own unique, sequential serial
number.
See also the further documentation in the area
• IP67: EtherCAT Box
• Safety: TwinSafe
Examples of markings:
Fig.1: EL5021 EL terminal, standard IP20 IO device with batch number and revision ID (since 2014/01)
Fig.2: EK1100 EtherCAT coupler, standard IP20 IO device with batch number
EL70x7 9Version 1.0
Foreword
Fig.3: CU2016 switch with batch number
Fig.4: EL3202-0020 with batch numbers 26131006 and unique D-number 204418
Fig.5: EP1258-00001 IP67 EtherCAT Box with batch number 22090101 and serial number 158102
Fig.6: EP1908-0002 IP76 EtherCAT Safety Box with batch number 071201FF and serial number 00346070
EL70x710 Version 1.0
Foreword
Fig.7: EL2904 IP20 safety terminal with batch number/date code 50110302 and serial number 00331701
EL70x7 11Version 1.0
Product overview
2 Product overview
2.1 EL7037
2.1.1 EL7037 - Introduction
Fig.8: EL7037
Stepper motor terminal, 24 V DC, 1,5 A, vector control
The The EL7037 EtherCAT Terminal is intended for stepper motors with low performance range. The PWM
output stages cover a wide range of voltages and currents. Together with two inputs for limit switches, they
are located in the EtherCAT Terminal.
The EL7037 can be adjusted to the motor and the application by changing just a few parameters. Stepper
motors from the AS10xx series can be operated with vector control. This control technique offers various
benefits, such as better dynamics and lower power consumption.
Together with a stepper motor, the EL7037 represents an inexpensive compact drive.
Quick links
Connection instructions
• Section "Installation and wiring",
- LEDs and pin assignment [}48]
- Connection examples [}50]
Commissioning instructions
• Section "Commissioning",
- Installation under TwinCAT [}58]
- Integration into the NC configuration [}104]
- Basic principles: "Positioning interface" [}140]
EL70x712 Version 1.0
Configuration instructions
• Section "Commissioning",
- Configuring the main parameters - Settings in the CoE register [}109]
- Configuring the main parameters - NC settings [}112]
• Section "Configuration with the TwinCAT System Manager",
- Object description and parameterization [}155]
Application example
• Section "Commissioning",
- Application example [}117]
Product overview
EL70x7 13Version 1.0
Product overview
2.1.2 EL7037 - Technical data
Technical data EL7037
Number of outputs 1 stepper motor, 2 phases
Number of digital inputs 2 limit position, 4 for an encoder system
Number of digital outputs 1 configurable for brake (0.5 A)
Supply voltage 24 V DC (-15 %/+20 %)
Output current 1.5 A (overload- and short-circuit-proof)
Operating modes Standard mode (velocity direct / position controller)
Field-oriented control (extended velocity mode /
extended position mode)
Sensorless operation
Travel distance control (positioning interface)
Maximum step frequency 1000, 2000, 4000, 8000 or 16000 full steps/s
(configurable)
Step pattern up to 64-fold micro stepping (automatic switching,
speed-dependent)
Current controller frequency approx. 30 kHz
Encoder pulse frequency maximum 400,000 increments/s (4-fold evaluation)
Input signal voltage "0" -3 V … 2 V
Input signal voltage "1" 2.5 V … 28 V
Input current typ. 5 mA
Diagnostics LED Warning strand A and B, error strand A and B, power,
enable
Resolution approx. 5,000 positions in typical applications (per
revolution)
Power supply via the E-bus, encoder/driver stage: via the power
contacts, motor: via terminal contacts
Current consumption from the E-bus typ. 100 mA
Electrical isolation 500 V (E-bus/signal voltage)
Support NoCoEStorage [}33]
Configuration no address setting required
Weight approx. 60 g
Permissible ambient temperature range during
operation
Permissible ambient temperature range during
storage
Permissible relative humidity 95%, no condensation
Dimensions (W x H x D) approx. 15 mm x 100 mm x 70 mm
Installation on 35 mm mounting rail according to EN 60715
Vibration / shock resistance Conforms to EN 60068-2-6 / EN 60068-2-27
EMC immunity/emission according to EN 61000-6-2 / EN 61000-6-4
EMC category Category C3 - standard
Protection class IP 20
Installation position
Approval CE
yes
Configuration via TwinCAT System Manager
0℃ ... +55℃
-25°C ... + 85°C
(connected width: 12 mm)
according to IEC/EN 61800-3
Category C2, C1 - auxiliary filter required
see note [}45]!
EL70x714 Version 1.0
2.2 EL7047
2.2.1 EL7047 - Introduction
Product overview
Fig.9: EL7047
Stepper motor terminal, 50 V DC, 5 A, vector control
The EL7047 EtherCAT Terminal is intended for stepper motors with medium performance range. The PWM
output stages cover a wide range of voltages and currents. Together with two inputs for limit switches, they
are located in the EtherCAT Terminal.
The EL7047 can be adjusted to the motor and the application by changing just a few parameters. 64-fold
micro-stepping ensures particularly quiet and precise motor operation.
Field-oriented control can be selected for AS1xxx series stepper motors from Beckhoff Automation. This
offers a number of advantages, such as a better dynamics and lower power consumption.
Together with a stepper motor and an encoder, the EL7047 represents an inexpensive small servo axis.
The LEDs indicate status, warning and error messages as well as possibly active limitations.
Quick links
Connection instructions
• Section "Installation and wiring",
- LEDs and pin assignment [}53]
- Connection examples [}55]
Commissioning instructions
• Section "Commissioning",
- Installation under TwinCAT [}58]
- Integration into the NC configuration [}104]
- Basic principles: "Positioning interface" [}140]
EL70x7 15Version 1.0
Product overview
Configuration instructions
• Section "Commissioning",
- Configuring the main parameters - Settings in the CoE register [}109]
- Configuring the main parameters - NC settings [}112]
• Section "Configuration with the TwinCAT System Manager",
- Object description and parameterisation [}179]
Application example
• Section "Commissioning",
- Application example [}117]
EL70x716 Version 1.0
Product overview
2.2.2 EL7047 - Technical data
Technical data EL7047
Number of outputs 1 stepper motor, 2 phases
Number of digital inputs 2 limit position, 4 for an encoder system
Number of digital outputs 1 configurable for brake (0.5 A)
Supply voltage 8 … 50 V DC
Output current 5 A (overload- and short-circuit-proof)
Operating modes Standard mode (velocity direct / position controller)
Field-oriented control (extended velocity mode /
extended position mode)
Sensorless operation
Travel distance control (positioning interface)
Maximum step frequency 1000, 2000, 4000, 8000 or 16000 full steps/s
(configurable)
Step pattern up to 64-fold micro stepping (automatic switching,
speed-dependent)
Current controller frequency approx. 30 kHz
Encoder pulse frequency maximum 400,000 increments/s (4-fold evaluation)
Input signal voltage "0" -3 V … 2 V
Input signal voltage "1" 2.5 V … 28 V
Input current typ. 5 mA
Diagnostics LED Warning strand A and B, error strand A and B, power,
enable
Resolution approx. 5,000 positions in typical applications (per
revolution)
Power supply via the E-bus, encoder/driver stage: via the power
contacts, motor: via terminal contacts
Current consumption from the E-bus typ. 140 mA
Electrical isolation 500 V (E-bus/signal voltage)
Support NoCoEStorage [}33]
Configuration no address setting required
Weight approx. 105 g
Permissible ambient temperature range during
operation
Permissible ambient temperature range during
storage
Permissible relative humidity 95%, no condensation
Dimensions (W x H x D) approx. 27 mm x 100 mm x 70 mm
Installation on 35 mm mounting rail according to EN 60715
Vibration / shock resistance Conforms to EN 60068-2-6 / EN 60068-2-27
EMC immunity/emission according to EN 61000-6-2 / EN 61000-6-4
EMC category Category C3 - standard
Protection class IP 20
Installation position
Approval CE
yes
Configuration via TwinCAT System Manager
0℃ ... +55℃
-25°C ... + 85°C
(connected width: 24 mm)
according to IEC/EN 61800-3
Category C2, C1 - auxiliary filter required
see note [}45]!
EL70x7 17Version 1.0
Product overview
2.3 Technology
The EL70x7 stepper motor terminal integrates a compact Motion Control solution for stepper motors in a
very compact design.
The user can control stepper motors in the low to medium performance range. With an output current of up
to 5 A, the EL7047 can achieve a considerable torque of e.g. 5 Nm at a standard stepper motor. The supply
voltage of up to 50 VDC allows high speeds with good torque and thus high mechanical performance. The
stepper motor and an incremental encoder can be connected directly to the EL70x7.
The stepper motor terminal provides three basic modes of operation.
In standard mode [}22] all unipolar and bipolar stepper motors that comply with the specifications of the
corresponding EL70x7 can be controlled. Two currents with sine/cosine curve are provided. The current is
clocked with 64 kHz and resolved with up to 64-fold microstepping to achieve a smooth current.
Extended mode [}23] is based on field-oriented control. This mode can only be used for stepper motors
from Beckhoff. The current is not only provided, but controlled in a comprehensive manner. Typical stepper
motor problems such as pronounced resonance are therefore finally a thing of the past. Furthermore, the
current is adjusted depending on the load, thereby enabling considerable energy savings and lower thermal
loads at the stepper motor.
In sensorless mode [}25] stepper motors from Beckhoff can be controlled load-dependent without a
feedback system.
Realisation of more demanding positioning tasks
More demanding positioning tasks can be realised via the TwinCAT automation software from Beckhoff. Like
other axes, the stepper motor terminals are integrated via the TwinCAT System Manager and can be used
like standard servo axes. Special stepper motor features, such as speed reduction in the event of large
following errors, are automatically taken into account via the stepper motor axis option. The effort for
changing from a servomotor to a stepper motor - and back - is no greater than changing from one fieldbus to
another one under TwinCAT.
The output stages of the stepper motor terminals have an overload protection in the form of an
overtemperature warning and switch-off. Together with short circuit detection, diagnostic data are accessible
in the process image of the controller. In addition, this status is displayed by the Bus Terminal LEDs, along
with other information. The output stage is switched on via an Enable-Bit. The motor current can be set and
reduced via a parameter value.
Optimum adaptation to the motor and the implementation of energy-saving features require minimum
programming effort. Since all data are set in the form of parameters in the CoE register, it is easily possible
to replace an EtherCAT Terminal or store certain parameters for transfer to the next project. It is therefore no
longer necessary to transfer certain potentiometer settings or to document DIP switch settings.
2.3.1 Stepper motor
Stepper motors are electric motors and are comparable with synchronous motors. The rotor is designed as a
permanent magnet, while the stator consists of a coil package. The frequency of the stator rotary field is
always in a fixed ratio relative to the rotor speed. In contrast to synchronous motors, stepper motors have a
large number of pole pairs. In a minimum control configuration, the stepper motor is moved from pole to pole,
or from step to step.
Stepper motors have been around for many years. They are robust, easy to control, and provide high torque.
In many applications, the step counting facility saves expensive feedback systems. Even with the
increasingly widespread use of synchronous servomotors, stepper motors are by no means "getting long in
the tooth". They are considered to represent mature technology and continue to be developed further in
order to reduce costs and physical size, increase torque and improve reliability. For a standard stepper
motor with 200 full steps, the best possible positioning accuracy is approx. 1.8°.
EL70x718 Version 1.0
Product overview
Today, the most widely used type in industry is the hybrid stepper motor type. In this type of motor the rotor
consists of a toothed iron core with one or a few permanent magnets in the rotor core. The rotor is designed
such that the polarity of successive teeth is inverse. This enables the production of motors with a high
number of steps, which is essential for positioning accuracy, combined with a relatively high torque. The
electrical behaviour of such a hybrid stepper motor is comparable with a multipole synchronous servomotor.
However, thanks to the synchronous toothing of stator and rotor, hybrid stepper motors offer a significantly
higher cogging torque.
Hybrid stepper motors with two or more phases are available on the market. Since the terminals described
here are designed for two-phase motors, the description focuses on the two-phase type, with the phases
referred as A and B in this documentation.
The development of the EL70x7 EtherCAT Terminals for the Beckhoff EtherCAT Terminal system opens up
new fields of application. The use of microstepping, the latest semiconductor technology and field-oriented
control (only with Beckhoff motors) offers many advantages:
• smoother operation
• avoidance of resonance
• reduced energy consumption
• lower thermal load on the motor
• minimum electromagnetic emissions
• long cable lengths
• simpler handling
• reduced size of the power electronics
• simple integration into higher-level systems
• integrated feedback system
Stepper motor parameters
• Mechanical system
Irrespective of the drive and the stepper motor itself, the configuration of the mechanism attached to the
motor shaft has significant influence on the achievable control quality.
Natural resonances, load resonances, gear backlash (loose) and static friction have negative affect on the
controllability of the drive system. This often requires "softer" controller parameterisation, which in turn leads
to a higher position lag in the system. Sliding friction can result in reduced efficiency (due to increased
energy demand), but on the other hand it can have a positive effect on the control stability, due to its
dampening effect.
As a general rule, the "stiffer" the mechanics of a drive system, the easier it is to control, which is beneficial
for achieving a small position lag in the drive system.
• Speed
Stepper motors have low maximum speed, which is usually specified as a maximum step frequency.
• Number of phases
Motors with 2 to 5 phases are common. The EL70x7 EtherCAT Terminals support 2-phase motors. 4-phase
motors are basically 2-phase motors with separate winding ends. They can be connected directly to the
EtherCAT Terminal.
• Torque
Refers to the maximum motor torque at different speeds. This parameter is usually represented by a
characteristic curve. Stepper motors have comparatively high torque in the lower speed range. In many
applications, this enables them to be used directly without gearing. Compared with other motors, stepper
motors can quite easily provide a holding moment of the same order of magnitude as the torque.
EL70x7 19Version 1.0
Product overview
• Cogging torque
In many cases the stepper motors design results in high cogging torque, which can lead to relatively strong
natural resonance in a motor- and load-dependent speed range. In relation to the cogging torque, increased
inertia often leads to a less strong resonance and smoother operation.
• Mass moment of inertia
In standard mode, the key parameter of the mechanical system is the mass moment of inertia JΣ. It is
essentially composed of the mass moment of inertia of the stepper motor rotor JM and the mass moment of
inertia of the connected load JL. The friction moment J
neglected in a first approximation.
and the moment of inertia of the encoder J
fric
can be
Enc
JƩ ≈ JM + J
L
The ratio between the load torque and the motor torque is defined by the constant kJ.
kJ ≈ JL / J
M
Fig.10: Simplified representation of the mass moments of inertia
As a first approximation, the coupling of the individual masses over the rotor shaft can be modelled as twomass oscillator. The resonance frequency between the motor and the encoder lies in a relatively high
frequency range, which is usually not relevant for stepper motor drives and is suppressed within the drive by
low-pass filtering. The resonance frequency between the motor and the load is frequently in the range
between 20 and 500 Hz. It is therefore often in the operating range of the drive control. Design measures to
reduce the influence of the load resonance include a small load ratio kJ and a rigid coupling of the motor
shaft to the connected load.
• Resonance
At certain speeds, stepper motors run less smoothly. This phenomenon is particularly pronounced when the
motor runs without coupled load, in which case it may even stop (in standard mode). This is caused by
resonance. A distinction can roughly be made between
• resonances in the lower frequency range up to approx. 250Hz; and
• resonances in the medium to upper frequency range.
Resonances in the medium to upper frequency range essentially result from electrical parameters such as
inductance of the motor winding and supply line capacity. They can be controlled relatively easily through
high pulsing of the control system.
Resonances in the lower range essentially result from the mechanical motor parameters. Apart from their
impact on smooth running, such resonances can lead to significant loss of torque, or even loss of step of the
motor, and are therefore particularly undesirable.
In principle, the stepper motor represents an oscillatory system (comparable to a mass/spring system),
consisting of the moving rotor with a moment of inertia and a magnetic field that creates a restoring force that
acts on the rotor. Moving and releasing the rotor creates a damped oscillation. If the control frequency
corresponds to the resonance frequency, the oscillation is amplified, so that in the worst case the rotor will
no longer follow the steps, but oscillate between two positions.
The EL70x7 EtherCAT Terminals prevent this effect thanks to their field-oriented control (Extended
Operation Modes) for all Beckhoff stepper motors.
EL70x720 Version 1.0
Product overview
•Torque constant
In the Extended Operation Modes the torque constant kT is used as an additional parameter for the
mechanical controlled system. It indicates the ratio between the torque-forming motor current and the active
torque at the shaft. However, since the field-oriented operating mode is not common for stepper motors, the
torque constant is usually not listed in the motor data sheet.
Electrical system
• Nominal voltage, supply voltage and winding resistance
Under steady-state conditions, the rated current at the rated voltage depends on the winding resistance. This
voltage should not be confused with the supply voltage of the power output stage in the EtherCAT Terminal.
The EL70x7 applies a controlled current to the motor winding. If the supply voltage falls below the nominal
voltage, the power output stage can no longer apply the full current, resulting in a loss of torque. It is
desirable to aim for systems with small winding resistance and high supply voltage in order to limit warming
and achieve high torque at high speeds.
• Induced countervoltage
Like servomotors, hybrid stepper motors induce a voltage ui [Vs/rad] in the stator winding of the motor, which
is proportional to the speed. It is also referred to as Back Electromotive Force (BEMF). In conjunction with
the DC link voltage (motor voltage), the induced countervoltage determines the physically achievable
maximum speed of the motor.
The ratio of the magnitude of the induced countervoltage and the motor speed varies depending on the
design and is described via the voltage constant ke.
ui = ke·ω
The motor parameter ke [mV/(rad/s)] is required for step loss recognition without encoder and for sensorless
control.
For stepper motors where the voltage constant is not specified in the data sheet, it can be relatively easily
determined using a digital multimeter. To this end the motor to be measured must be operated (within the
rated speed range) by an auxiliary motor via a coupling with constant speed. The motor phases of the motor
to be measured must be open (not connected to the terminal or shorted). The multimeter can then be used
to determine the RMS value of the induced countervoltage, and therefore the voltage constant, at one of the
two open motor phases (A or B).
m
• Step angle
The step angle indicates the angle travelled during each step. Typical values are 3.6°, 1.8° and 0.9°. This
corresponds to 100, 200 and 400 steps per motor revolution. Together with the downstream transmission
ratio, this value is a measure for the positioning accuracy. For technical reasons, the step angle cannot be
reduced below a certain value. Positioning accuracy can only be improved further by mechanical means
(transmission). An elegant solution for increasing the positioning accuracy is the microstepping function
offered by the EL70x7. It enables up to 64 intermediate steps. The smaller "artificial" step angle has a further
positive effect: The drive can be operated at higher speed, yet with the same precision. The maximum speed
is unchanged, despite the fact that the drive operates at the limit of mechanical resolution.
• Winding resistance, winding inductance
The winding inductance and winding resistance of the stepper motor stator determine the electrical motor
time constant Te = L / R, which is a key parameter for current controller configuration.
Specifying the stepper motor
1. Determine the required positioning accuracy and hence the step resolution. The first task is to
determine the maximum resolution that can be achieved. The resolution can be increased via
mechanical gear reduction devices such as spindles, gearing or toothed racks. The 64-fold
microstepping of the stepper motor terminals also has to be taken into account.
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2. Determine mass m and moment of inertia (J) of all parts to be moved
3. Calculate the acceleration resulting from the temporal requirements of the moved mass.
4. Calculate the forces from mass, moment of inertia, and the respective accelerations.
5. Convert the forces and velocities to the rotor axis, taking account of efficiencies, moments of friction
and mechanical parameters such as gear ratio. It is often best to start the calculation from the last
component, usually the load. Each further element transfers a force and velocity and leads to further
forces or torques due to friction. During positioning, the sum of all forces and torques acts on the
motor shaft. The result is a velocity/torque curve that the motor has to provide.
6. Using the characteristic torque curve, select a motor that meets these minimum requirements. The
moment of inertia of the motor has to be added to the complete drive. Verify your selection. In order to
provide an adequate safety margin, the torque should be oversized by 20% to 30%. The optimisation
is different if the acceleration is mainly required for the rotor inertia. In this case, the motor should be
as small as possible.
7. Test the motor under actual application conditions: Monitor the housing temperatures during
continuous operation. If the test results do not confirm the calculations, check the assumed
parameters and boundary conditions. It is important to also check side effects such as resonance,
mechanical play, settings for the maximum operation frequency and the ramp slope.
8. Different measures are available for optimising the performance of the drive: using lighter materials or
hollow instead of solid body, reducing mechanical mass. The control system can also have significant
influence on the behaviour of the drive. The Bus Terminal enables operation with different supply
voltages. The characteristic torque curve can be extended by increasing the voltage. In this case, a
current increase factor can supply a higher torque at the crucial moment, while a general reduction of
the current can significantly reduce the motor temperature. For specific applications, it may be
advisable to use a specially adapted motor winding.
2.3.2 Standard mode
Stepper motors were originally operated with very simple output stages, which were only able to switch the
voltage of the motor phases separately (nowadays current control takes place via PWM with pulse-width
modulation as standard). Initially the motor phases there were controlled individually in turn. A switching
sequence in the positive direction of rotation corresponds to the switching sequence (+A, +B, -A, -B).
Sequential switching results in rather irregular operation in this mode. In order to make the operation
smoother, so-called microstepping was introduced later, in which the four set voltages were extended by
intermediate values (e.g. from a stored sine table). These days, microstepping based on 64 steps is
commonly used.
Fig.11: Control structure of a standard stepper motor drive
Neglecting the sampling resulting from the microstepping, the motor current I as function of the electrical
angle φe and of the magnitude of the motor current I
(when using a current controller) can be described as
ABS
follows:
I(φe) = IA+ jIB= I
cos(φe) + jI
ABS
ABS
sin(φe)
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Represented by magnitude and angle:
I(φe ) = I
ABS
· e
jφe
It follows that a rotation of the electrical angle φe is equivalent to four full steps. (A stepper motor with 200
full steps therefore has 50 pole pairs).
The shaft aligns itself if a constant current is set with no load at the motor shaft. Within a pole pairs the shaft
points in the direction of the active stator field.
If an external load is applied to the motor shaft, the shaft is turned out of the field direction, resulting in a load
angle (also referred to as angular displacement) (relative to an electric rotation of the angle φe). The load
angle depends on the design of the stepper motor itself, the motor current and the torque acting on the shaft.
The relationship is non-linear!
If the load angle exceeds a motor-dependent maximum value (i.e. if the maximum machine torque under
these boundary conditions is exceeded), the load torque can no longer be maintained by the motor. If the
shaft is turned further out of the rotary field, it "tips", resulting in one or more step losses. The "tip angle" may
vary between motor types. Often, it lies between around 45° and 65°.
Fig.12: Behaviour of the rotor under load
The load angle is of interest for the user, because it allows conclusions about the load on the shaft. It is
measured by evaluating the induced countervoltage* and can be used to optimise the drive system.
2.3.3 Field-oriented control
In the Extended Operation Modes the stepper motor is operated like a servomotor, based on the principle of
field-oriented control.
Function
The operating behaviour of the motor corresponds to that of a traditional DC motor, with commutation via a
mechanical commutator. With a constant exciter field, the torque of the DC machine is directly proportional to
the stator current and can be directly influenced by it. The exciter field is generated, depending on the
machine type, by permanent magnets or, with a separately excited DC machine, for example, via a separate
excitation winding.
Fig.13: Coordinate transformation of field-oriented control
For servomotors and also hybrid stepper motors, initially there is no direct link between the phase currents
and the torque. Field and torque are decoupled mathematically via Park's transformation. Two current
components, "d" for "direct" in field direction and "q" for "quadrature" in torque-forming direction, are
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calculated from the phase currents. Via the torque-forming current component iq, the torque of the machine
can now be regulated directly, like for a DC machine.
A prerequisite is that the rotor position is available with sufficiently high accuracy. For a stepper motor the
encoder resolution should be at least 4000 increments per mechanical revolution, in order to achieve
adequate positioning accuracy. The minimum encoder resolution also depends on the number of full steps
and can be calculated approximately as follows.
Fig.14: Calculation of the resolution
Commutation determination for Extended Operation Modes
Because the absolute actual position is not available for incremental encoders, on system start-up there is
no direct reference to the rotor position, which is required for field-oriented operation. Therefore, the
reference between the actual position and the rotor position must be generated at start-up via a commutation
determination process. During this process the rotor is moved forward and back several times up to two full
steps.
Commutation determination
• The maximum current should be set just below the rated motor current.
Note
• During commutation determination the rotor shaft should not be subject to an external
torque. If this condition is not met, the Extended Operation Modes cannot be used.
Control structure
The drive control structure is a cascade control structure with a position control loop and a lower-level speed
and current control loop. If a speed setpoint is specified, the external position control loop can be omitted.
Fig.15: Cascade control structure with field-oriented control (Extended Operating modes)
Motor dependency
Due to the fact that the control is strongly dependent on the motor parameters, the controller parameters and
motor behaviour itself, field-oriented control is limited to Beckhoff motors. This mode is not supported for
motors from other manufacturers.
Main advantages compared with standard mode
• Low current consumption (almost full load-dependence)
• High efficiency
• Consistent dynamics compared with standard mode
• Step losses are inherently avoided
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Requirement
• Encoder with sufficiently high resolution required (minimum 4000 [INC/360°])
• Slightly higher parametrisation effort required (speed controller)
• Commutation determination at startup (due to incremental encoder)
• Only possible with stepper motors from Beckhoff Automation (AS10xx)
2.3.4 Sensorless operation
Because the default operation of a stepper motor with a constant load-independent current is not energyefficient and leads to a permanently high thermal load, efforts are made to reduce this load.
Function
By analyzing the speed-proportional induced countervoltage, it is possible to control the stator current
depending on the load with the aid of a machine model (without sensor/encoder), thereby significantly
increasing the efficiency.
Since this operating mode requires a minimum amplitude of the magnitude of the induced countervoltage,
sensorless control only works in the medium and upper speed range. In the lower speed range the motor is
operated in standard mode. The changeover to sensorless operation take place via a programmable, motordependent switching speed. The switching speed is usually in the range between half and three revolutions
per second (crossover velocity 1).
When sensorless control is activated, the transient phenomenon results in a slight mechanical jerk of the
shaft, which is proportional to the load acting on the shaft.
Fig.16: Influence of the crossover velocity thresholds (1,2,3) on sensorless control
After switching on, the control current remains constant up to a second configurable speed and is reduced to
a third parameterizable speed via a linear ramp.
A long control current ramp leads to a stronger stabilization of the transient phenomenon of the control.
However, it also leads to a longer flowing constant motor current and therefore slightly higher losses.
Motor dependency
Due to the fact that the control is strongly dependent on the motor parameters, the controller parameters and
motor behaviour itself, sensorless operation is limited to Beckhoff motors. This mode is not supported for
motors from other manufacturers.
Parameterisation
Compared to the other operating modes, the parameterisation effort is relatively high. However, all the
required necessary parameters are pre-specified via a startup list for the respective motor types. All that is
required during commissioning is an adjustment of the speed control parameters, due to the given mass
inertia ratios of the connected loads in the mechanical system.
For the speed controller, in principle the same dependence on the mass moment of inertia and the torque
constant applies as in the Extended Operation Modes. Thanks to the lower-level sensorless control it is,
however, possible to achieve a better overall result through different parameterisation.
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All parameters required for sensorless operation can be found in the table "Overview of parameter settings
for individual operating modes [}124]".
Summary
In this mode, above a minimum speed the motor current without encoder is controlled load-dependent. In
this way it is possible to realise a particularly cost-effective drive in combination with high efficiency. The
achievable dynamic performance of the drive control is slightly reduced compared to the other operating
modes.
Advantages compared with standard mode
• Low current consumption (almost full load-dependence)
• High efficiency
• no encoder required
Prerequisites
• relatively high parameterisation effort required (speed controller + additional parameters)
• minimum speed required (if the speed is too low, the motor automatically switches to standard mode)
• dynamic performance somewhat lower than in standard mode
• Only possible with stepper motors from Beckhoff Automation (AS10xx)
2.4 Start-up
For commissioning:
• Install the EL70x7 as described in section Installation [}38].
• Configure the EL70x7 in TwinCAT as described in section Commissioning [}58].
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3 Basics communication
3.1 EtherCAT basics
Please refer to the chapter EtherCAT System Documentation for the EtherCAT fieldbus basics.
3.2 EtherCAT cabling – wire-bound
The cable length between two EtherCAT devices must not exceed 100 m. This results from the FastEthernet
technology, which, above all for reasons of signal attenuation over the length of the cable, allows a maximum
link length of 5 + 90 + 5 m if cables with appropriate properties are used. See also the Design
recommendations for the infrastructure for EtherCAT/Ethernet.
Cables and connectors
For connecting EtherCAT devices only Ethernet connections (cables + plugs) that meet the requirements of
at least category 5 (CAt5) according to EN 50173 or ISO/IEC 11801 should be used. EtherCAT uses 4 wires
for signal transfer.
EtherCAT uses RJ45 plug connectors, for example. The pin assignment is compatible with the Ethernet
standard (ISO/IEC 8802-3).
Pin Color of conductor Signal Description
1 yellow TD + Transmission Data +
2 orange TD - Transmission Data -
3 white RD + Receiver Data +
6 blue RD - Receiver Data -
Due to automatic cable detection (auto-crossing) symmetric (1:1) or cross-over cables can be used between
EtherCAT devices from Beckhoff.
Recommended cables
Suitable cables for the connection of EtherCAT devices can be found on the Beckhoff web-
Note
site!
E-Bus supply
A bus coupler can supply the EL terminals added to it with the E-bus system voltage of 5 V; a coupler is
thereby loadable up to 2A as a rule (see details in respective device documentation).
Information on how much current each EL terminal requires from the E-bus supply is available online and in
the catalogue. If the added terminals require more current than the coupler can supply, then power feed
terminals (e.g. EL9410) must be inserted at appropriate places in the terminal strand.
The pre-calculated theoretical maximum E-bus current is displayed in the TwinCAT System Manager. A
shortfall is marked by a negative total amount and an exclamation mark; a power feed terminal is to be
placed before such a position.
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Fig.17: System manager current calculation
Caution! Malfunction possible!
The same ground potential must be used for the E-Bus supply of all EtherCAT terminals in
Attention
a terminal block!
3.3 General notes for setting the watchdog
ELxxxx terminals are equipped with a safety feature (watchdog) that switches off the outputs after a
specifiable time e.g. in the event of an interruption of the process data traffic, depending on the device and
settings, e.g. in OFF state.
The EtherCAT slave controller (ESC) in the EL2xxx terminals features 2 watchdogs:
• SM watchdog (default: 100 ms)
• PDI watchdog (default: 100 ms)
SM watchdog (SyncManager Watchdog)
The SyncManager watchdog is reset after each successful EtherCAT process data communication with the
terminal. If no EtherCAT process data communication takes place with the terminal for longer than the set
and activated SM watchdog time, e.g. in the event of a line interruption, the watchdog is triggered and the
outputs are set to FALSE. The OP state of the terminal is unaffected. The watchdog is only reset after a
successful EtherCAT process data access. Set the monitoring time as described below.
The SyncManager watchdog monitors correct and timely process data communication with the ESC from the
EtherCAT side.
PDI watchdog (Process Data Watchdog)
If no PDI communication with the EtherCAT slave controller (ESC) takes place for longer than the set and
activated PDI watchdog time, this watchdog is triggered.
PDI (Process Data Interface) is the internal interface between the ESC and local processors in the EtherCAT
slave, for example. The PDI watchdog can be used to monitor this communication for failure.
The PDI watchdog monitors correct and timely process data communication with the ESC from the
application side.
The settings of the SM- and PDI-watchdog must be done for each slave separately in the TwinCAT System
Manager.
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Fig.18: EtherCAT tab -> Advanced Settings -> Behavior -> Watchdog
Notes:
• the multiplier is valid for both watchdogs.
• each watchdog has its own timer setting, the outcome of this in summary with the multiplier is a
resulting time.
• Important: the multiplier/timer setting is only loaded into the slave at the start up, if the checkbox is
activated.
If the checkbox is not activated, nothing is downloaded and the ESC settings remain unchanged.
Multiplier
Multiplier
Both watchdogs receive their pulses from the local terminal cycle, divided by the watchdog multiplier:
1/25 MHz * (watchdog multiplier + 2) = 100 µs (for default setting of 2498 for the multiplier)
The standard setting of 1000 for the SM watchdog corresponds to a release time of 100 ms.
The value in multiplier + 2 corresponds to the number of basic 40 ns ticks representing a watchdog tick.
The multiplier can be modified in order to adjust the watchdog time over a larger range.
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Example "Set SM watchdog"
This checkbox enables manual setting of the watchdog times. If the outputs are set and the EtherCAT
communication is interrupted, the SM watchdog is triggered after the set time and the outputs are erased.
This setting can be used for adapting a terminal to a slower EtherCAT master or long cycle times. The
default SM watchdog setting is 100 ms. The setting range is 0..65535. Together with a multiplier with a range
of 1..65535 this covers a watchdog period between 0..~170 seconds.
Calculation
Multiplier = 2498 → watchdog base time = 1 25 MHz * (2498 + 2) = 0.0001 seconds = 100 µs
SM watchdog = 10000 → 10000 * 100 µs = 1 second watchdog monitoring time
CAUTION! Undefined state possible!
The function for switching off of the SM watchdog via SM watchdog = 0 is only imple-
CAUTION
CAUTION
mented in terminals from version -0016. In previous versions this operating mode should
not be used.
CAUTION! Damage of devices and undefined state possible!
If the SM watchdog is activated and a value of 0 is entered the watchdog switches off completely. This is the deactivation of the watchdog! Set outputs are NOT set in a safe state, if
the communication is interrupted.
Outputs in SAFEOP state
The default set watchdog monitoring sets the outputs of the module in a safe state - de-
Note
pending on the settings in SAFEOP and OP - e.g. in OFF state. If this is prevented by deactivation of the watchdog monitoring in the module, the outputs can be switched or set
also in the SAFEOP state.
3.4 EtherCAT State Machine
The state of the EtherCAT slave is controlled via the EtherCAT State Machine (ESM). Depending upon the
state, different functions are accessible or executable in the EtherCAT slave. Specific commands must be
sent by the EtherCAT master to the device in each state, particularly during the bootup of the slave.
A distinction is made between the following states:
• Init
• Pre-Operational
• Safe-Operational and
• Operational
• Boot
The regular state of each EtherCAT slave after bootup is the OP state.
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