BECKHOFF DK9222-0909-0012 User Manual

I/O

Application Note DK9222-0909-0012

Bus Terminal

Pulse Train Output Terminal KL2521

Keywords

Encoder simulation
Pulse Train
Stepper motor
Pulse direction signal
Fieldbus substitute
Servo controller
Servo drive
Frequency converter
KL2521

This Application Example describes the control and positioning of drives through pulse patterns (pulse

train), which is common practice in Asia and the USA. In servo or stepper motors this technique is used for

realising simple positioning tasks. The pulses can be generated in the PLC or an associated I/O module, e.g.

Bus Terminal KL2521. It modulates a binary signal with a specified frequency that can be used directly for

control purposes.

The idea is that with the new KL2521 Pulse Train output terminal, Beckhoff are using simple pulses sent to stepper motors

and servo drives to implement digital technology for precise positioning tasks. To do this, the electronic Bus Terminal converts

a binary signal to a frequency, feeding this, electrically isolated from the terminal bus, to the positioning drive. The frequency

is preset by a 24 bit value from the automation unit. The advantage over conventional technology, such as an analog ± 10 V

interface, is that the Bus Terminal‘s high output frequency of 500 kHz allows the operation of the fastest servo drives currently

available. In contrast to analog technology, the set value signal is communicated without any offset drift. The 24 bit resolution

guarantees a high precision, in steps of 10 mHz. This means that set values can be specified in fine, almost continuous, steps.

In practice, the desired maximum output frequency is entered into a register, and then the frequency output can be used much

like a ± 10 V output by using 16 bits of the process image.

For application notes see disclaimer on the last page

Beckhoff

New Automation Technology

1

Application Note DK9222-0909-0012

Bus Terminal KL2521

Set value outputs by
variable frequency

+A

-A

+B

-B

24 V DC

Target/
following error

i. e.
Servoamplifiers,
frequency converters

Servomotors

Set value outputs

Target output

Bus Terminal

I/O

Fig. 1 Connections of the KL2521 pulse train terminal

Set value outputs and the acquisition of actual positions with just one Bus Terminal

The use of the Pulse Train technology to position drives is primarily used in Asia and in the USA. Its origins lie in the

methods for driving stepper motors. The wide acceptance and easy use of the technology resulted in its application to higher

power sectors of drive technology. The interface using Pulse Train technology is nowadays also applied to servoamplifiers

and frequency converters. The user can employ a consistent software and hardware interface, from micro-steppers up to

highpowered servo-drives.

Fig. 2 Set value outputs and the acquisition of actual positions with just one Bus Terminal

For application notes see disclaimer on the last page

Beckhoff

New Automation Technology

2