Mitsubishi Electronics A173SH, A172SH, A171SH User Manual

Positioning Control

Training Manual

Positioning Control

Cautions on Safety

Make sure to read the manuals and pay careful attention to safety when designi ng a system. In practice, pay attention to the following contents and handle any products or dem onstration units correctly.

Cautions on practice

DANGER

• Never touch any terminal while the power is supplied. If you touch a terminal, you may get an electrical shock.

• Turn off the power before connecting / disconnecting units, or opening any safety covers.

• Never insert your hand or any other object into a moving part.

CAUTION

• Never change the wiring or configuration of demonstration euipment without permission or if you are unsure of how to configure a system correctly. Such actions may cause failure, malfuncti on, injury or fire.

• If a simulation unit (such as an X-Y table) generates an abnormal smell or sound, immediately turn off the power switch.

• If you detect any abnormality, immediately turn off the power and contact a qualified engineer.

Positioning Control

Manual number: JY992D89901 Manual revision: A

Date : July 2000

Positioning Control

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iii

Positioning Control

Introduction

This manual describes basic oper ation for those who learn positioni ng control for the first ti me, the aim being so that they can get training using demonstration units of Mitsubishi FA equipment.

The following relevant manuals are available and should be referred to

FX-10GM/FX(E)-20GM Hardware and Programming manual JY992D60401 FX-10GM Users Guide JY992D68401

-10GM/FX2N-20GM Hardware and Programming manual JY992D77801

FX FX2N-10GM Users Guide JY992D77701 FX2N-20GM Users Guide JY992D77601 FX-PCS-VPS Win-E Software Manu al JY992D86801

-10GM/FX2N-20GM Connection Manual JY992D81601

Manual Name Number

Positioning Control

Positioning Control Contents

1. The World of Positioning Control...........................................................1-1

1.1 Welcome to the new world! .................................................................................1-1

1.2 Divers ifi e d a c tu a tors..................... .. .. ........................... .. .. ........................... .. .. .....1-2

1.3 Positioning method type......................................................................................1-4

2. Positioning by AC Servo System...........................................................2-1

2.1 When an AC servo system is introduced........................ ........................ .............2-1

2.2 Examples of AC servo systems....................... .. ........................ .. ........................2-3

3. Components of Positioning Control and Their Roles ............................3-1

3.1 Positioning controller ...........................................................................................3-4

3.1.1 Command pulse and feed quantity............................................................................3-4

3.1.2 Command pulse and feed speed ..............................................................................3-4

3.1.3 Setting the acceleration/deceleration time ................................................................3-5

3.1.4 Backlash correction function ........... ...... ....... ...... ...... .................................................3-5

3.1.5 Zero point return function ..........................................................................................3-6

3.2 Servo amplifier and servo motor.......................... ................................................3-7

3.2.1 Positioning control in accordance with command pulse............................................3-7

3.2.2 Deviation counter function.........................................................................................3-7

3.2.3 Servo lock function....................................................................................................3-7

3.2.4 Regenerative brake function .....................................................................................3-8

3.2.5 Dynamic brake function...................................... ...... ....... ...... ....... .............................3-8

3.3 Drive mechanism......................................................................... ....................... .3-9

3.3.1 Concept of drive system movement quantity ............................................................3-9

3.3.2 Setting the target position........................................................................................3-11

4. Advanced Positioning............................................................................4-1

4.1 Interpolation control.............................................................................................4-1

4.2 Other con t ro ls ................................. .. ... .......................... .. .. ........................... .. .. ... 4 -3

5. Actual Positioning..................................................................................5-1

5.1 Demons tr a ti o n E q u ip me n t ..................... .. .. ........................... .. .. ...........................5-1

5.1.1 Basic Set ...................................................................................................................5-1

5.1.2 Comprehensive Set...................................................................................................5-1

5.2 Operation of the demonstration equipment .........................................................5-2

5.2.1 Program example......................................................................................................5-3

5.2.2 Writing the program...................................................................................................5-4

5.2.3 Parameters................................................................................................................5-5

5.2.4 Operation...................................................................................................................5-7

6. Product Line up .....................................................................................6-1

6.1 Position controller ................................................................................................6-1

6.2 Servo am p lif ie r... ........................... .. .. ........................... .. .. ........................... .. .. .....6-5

6.3 Servo moto r ..................... .. .. ........................... .. .. ........................... .. .. ..................6-7

Appendix A:.............................................................................................. A-1

A-1: Tentative Selection of Motor Capacity................................. ........................ .. ......A-1

A-1-1: Motor effective torque...................... ...... ....... ...... ...... ....... ...... ....... .............................A-2

A-1-2: Load inertia moment..................................................................................................A-4

vii

Positioning Control Contents

viii

Positioning Control The World of Positioning Control 1

1 The World of Positioning Control

2 Positioning by AC Servo Sys tem

3 Components of Positioning Control and Their Roles

4 Advanced Positioning

5 Actual Positioning

6 Product Line up

A Appendix A: Tentative Selection of Motor Capacity

Positioning Control

1. The World of Positioning Control

1.1 Welcome to the new world!

The positioning controller, together with the programmable controller, personal computer and operator interface, is one of the four main units of FA (facto ry automation).

Among them, the positioning controller is important as the basis of FA, and regarded as the center of the mechatronics field in which many senior engineers have been playing active parts.

Positioning is all about motion, and motion often involves speed and precision. As speed can be related to productivity, it is an area of much development. But, when the machine speed increases, a problem with the stop precision is often generated. In order to solve this problem, diversified grades of position controllers have been required and developed.

Improvement of the machine efficiency generates immeasurable added value, including reduction of labour and the machine floor area for the same quantity of production.

The World of Positioning Control 1

If there are no problems related to the pos itioning aspe ct of a ma chine, it may mean that the machine is not running most efficiently. Here is where the science of developing an optimum positioning control system comes in.

1-1

Positioning Control The World of Positioning Control 1

1.2 Diversified actuators

• A power source which moves an element in a system is called actuator. A unit which detects a position of a work piece or moving part is called sensor.

• Diversified actuators and sensors, from simple ones to enhanced ones, are used in positioning.

• This paragraph describes representat ive types, their features and weak points.

Pneumatic

• Air source and high grade piping are required.

• High torque is not available.

• Multi-point positioning is complex and very difficult to achieve.

• Change in pos it ion ing is difficul t.

Brake motor

• Positioning mechanism is simple.

• Repeatability is poor.

• Change in pos it ion ing is difficul t.

(When optical sensors or limit switches are used for stop)

Clutch brake

• Frequent positioning is available.

• Life of friction plate is limited.

• Change in pos it ion ing is difficult.

(When optical sensors or limit switches are used for stop)

1-2

Positioning Control The World of Positioning Control 1

Stepping motor

• Positioning mechanism is simple.

• If load is heavy, motor may step out and displacement can occur.

• Motor capacity is small.

• Precision is poor at high speed.

DC servo system

• Positioning precision is good.

• Maintenance is required for motor brushes.

• It is not suitable for rotation at high speed.

General purpose inverter and general

purpose motor

• Multi-speed positioning is available using high-speed counter.

• High precision positioning is not available.

• Large torque is not available at start. (Specialized inverter is required)

AC servo system

• Precision is good.

• Maintenance is not required.

• Positioning address can be easily changed.

• It is compact, and offers high power.

1-3

Positioning Control The World of Positioning Control 1

1.3 Positioning method type

1) There are three types of positioning method

Control method Description Schematic drawing

Two limit switches are

Moving part

Ball screw

Limit switch for changeover to low speed

Limit switch for stop

High speed

Low speed

Movement

distance

Speed control

Limit switch method

provided in places where a systems moving part passes. At the first limit switch, the motor speed is reduced. At the second limit switch, the motor turns off and the brake turns on, to stop the moving part. In this method, because position controllers are not required, the system configuration can be realized at reasonable cost.

(Guideline of stopping precision: Approximately ±1.0 to 5.0 mm)*

B IM

INV

DC0 to 10V

IM: Inductive motor B: Brake INV: Inverter

Position control

Pulse count method

Pulse command method

A position detector (such as pulse encoder) is set up in a motor or rotation axis. The pulse number generated from the position detector is counted by a high-speed counter. When the pulse number reaches the preset value, the moving part stops. In this method, because limit switches are not used, the stop position can be easily changed.

An AC servo motor which rotates in proportion to the input pulse number is used as the drive motor. When the pulse number corresponding to the movement distance is input to the servo amplifier of the AC servo motor, positioning can be performed at high speed in proportion to the pulse frequency.

Pulses are fed back.

PLG

INV

DC0 to

High-speed counter unit

Pulses are fed back.

PLG SM

Servo

amplifier

Command pulse

Position controller

Moving part

IM: Inductive motor PLG: Pulse generator INV: Inverter PLC: Programmable cont rol l er

10V

High speed

Movement distanc e

Moving part

SM: Servo motor PLG: P ul s e generator PLC: Programmable

Movement distance

Ball screw

Low speed

Ball screw

controller

*1 The stop precision shows a value in a case where low speed is 10 to 100 mm/s.

1-4

Positioning Control The World of Positioning Control 1

2) Positioning method and stop precision

Velocity

Stop command

Velocity

Heavy load Small inertia

Stop command

Coasting distance

Speed reduction start Time delay

Light load Large inertia

Dispersion in s to p

Stop

Time

Stop

< Limit switch method >

- When automatically stopping a moving part driven by a motor, stop the motor by a position signal, detected by a limit switch (in general conditions, turn on the brake at the same time).

- The moving part continues by a coasting distance until it completely stops, after the stop command is given. The coasting distance is shaded in the figure.

- The stop precision is equivalent to the dispersion in the shaded area as shown in the figure on the left. The dispersion is affected by the speed when the stop command is given, the load size and the time delay since the stop command is given, until speed reduction actually starts.

Time

Velocity

High speed

Speed reduction command

Dispersion in speed reduction distance

Dispersion in stop

Time

Stop command

- If the required stop precision is not satisfactory when stopping from the normal operation speed, t he most effective method to improve the stop precision is to reduce the operation speed.

- However, if the operation speed is simply reduced, the machine efficiency may also be reduced. In actual operation, the motor speed can be reduced fro m high sp eed to low speed once, then the motor stopped.

1-5

Positioning Control The World of Positioning Control 1

< Pulse count method >

- When a pulse encoder is attached to a moving par t, and the mot or speed is c ontrol led by a number steps while the pulse number is counted, the movement qu antity per pulse is determined in accordance with the relationship between the pulse number generated by one rotation of the encoder, and the movement quantity of the mov ing part (workpiece) realized by one rotation of the motor. The movement quantity per pulse is regarded as the minimum unit for the stop command.

- However, the coasting distance at stop is not eliminated.

< Pulse command method >

- In this method using a servo system, the weak points described above are improved. A pulse encoder is attached to the servo motor, detecting the motor rotation quantity (workpiece movement distance), to continuously and directly control the speed from the high-speed operation to the t arget p osit ion, which all ows the wor kpiece t o stop wi th good precision.

- As the coasting distance at stop is eliminated, the positioning precision is improved.

1-6

Positioning Control Positioning by AC Servo System 2

1 The Wor l d of Positioning Control

2 Positioning by AC Servo System

3 Components of Positioning Control and Their Roles

4 Advanced Positioning

5 Actual Positioning

6 Product Line up

A Appendix A: Tentative Selection of Motor Capacity

Positioning Control

2. Positioning by AC Servo System

2.1 When an AC servo system is introduced

• Positioning can be performed by many diversified methods. Recently, AC servo methods which offer many advantages are often introduced.

• In the positioning system of an AC servo method, a position controller, servo amplifier and servo motor are generally required. The representative system configu ration is shown below.

Servo amplifier

Commercial

power supply

Converter



Smoothing

circuit

Inverter

DC ACDCAC DC

Positioning by AC Servo System 2

Servo motor

Command

pulse

Position

controller

The position controller generates a specified quantity of forward rotation (or reverse rotation) pulses at a specified frequency.

Deviation

counter

Why is the AC servo system attracting attention?

Speed

command

Current

control

The command pulse number is subtracted by the feedback pulse number, and the speed command to drive the servo motor is made from the deviation (accumulated pulse number). When the accumulated pulse number becomes 0, the servo motor stops.

PWM (pulse width modulation) control

AC servo systems are easier to h andle than hydraulic equipment.

Feedback

current

Feedback

The servo motor is equipped with a built-in encoder (pulse generator), dedicated to high speed response, and suitable to positioning control.

PLG

Encoder

pulse

The AC servo system satisfies the needs for multi-model small-lot production through only simple changes in the program.

As an AC servo system can generate large torque, it can satisfy the needs for down sizing and high power.

- Release from oil management

Robots in conjunction with an AC ser vo system can satisfy the needs for labor saving and automation.

- Release from dangerous, hard and dirty working environments

2-1

Positioning Control Positioning by AC Servo System 2

In the latest AC servo systems, conventional wea k points have been improved as follows.

- Though the latest systems are completely digital, they are equipped with parameters in conformance to diversified mechanical specifications and electrical specifications so that simple setting is possible.

- As frequent operation is enabled by a low inertia motor, the maximum torque is increased and the system can be applied to diversified machines.

- The latest systems are equipped with an auto tuning function, with which the servo amplifier automatically detects the load inertia moment and adjusts the gain. This is possible even if the load inertia moment is unknown.

Aspects described below are now incorperated to AC serv o systems which offer marked improvements from previous products.

In FA work place, a downsized AC servo system occupying less space is required!

In accordance with sever operation conditions, a tougher AC servo system is required!

An AC servo system anyone can handle easily is required! Even if the performance is good, the AC servo system cannot be accepted if it is difficult to handle.

Compact and light servo

system

Robust servo system

Easy servo system

An AC servo system givi ng suf f icie nt cost performance is required!

Good cost performance servo

system

2-2

Positioning Control Positioning by AC Servo System 2

2.2 Examples of AC servo systems

• Positioning indicates the operation to move an element, such as a workpiece or tool (dril l or cutter) from a certain position (point) to another target position (point) and stop it with high efficiency and high precisi on.

• In other words, the principle of positioning is the control of speed in accordance with the position, performed to promptly eliminate the remaining distance to the target position. The flexibility to change the target position electrically and easil y is an important requirement.

• Several cases of positioning using an AC servo motor are systemati cally shown below.

Constant feed

In the press/shear process for cutting, punching, etc., the processed material is positioned with high precision to produce a constant sized product.

Tapping

In order to tap a workpiece, "1. Quick feed", "2. Cutting feed" and "3. Quick return" are repeatedly performed.

Drilling in steel sheet

In order to perform processing on a flat face, positioning with high precision is performed by two motors (X axis feed motor and Y axis feed motor).

2-3

+ 51 hidden pages

Mitsubishi Electronics A173SH, A172SH, A171SH User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Cautions on Safety

Introduction

1 The World of Positioning Control

1.1 Welcome to the new world!

1.2 Diversified actuators

1.3 Positioning method type

2 Positioning by AC Servo System

2.1 When an AC servo system is introduced

2.2 Examples of AC servo systems