Adapting Parameters

Important Note

Please note the following warning points:

!

Harm to health or damage to assets is to be expected.

To avoid injury and damage to property, please note the following:

• Install an Emergency-Off switch in the area of the control system. This is the only possible way for you to ensure that the system can be safely switched off in case of control system failure.

• Install Hardware limit switches which affect the drive converters of all drives directly.

• Make sure that no one has access to system areas in which moving parts exist.

• Parallel control and monitoring via your program and STEP7 interface can cause conflicts which result in indefinite effects.

3.5.1 How to Determine Module Parameters

The "Increments per encoder revolution" parameters of the connected incremental encoder are found on its rating plate or in the technical data sheet.

The technology evaluates the encoder signals in quadruple mode.

Four pulses are proportional to one encoder increment. All distance specifications are referenced to pulse units.

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• You must calculate the "Maximum speed" parameter. Prerequisite is that you know the rated rpm of the drive (with +/-10 V at the analog output). You can find this information in the technical specification of your drive. If the encoder is mounted to the motor via a gear, you must take the gear ratio into account because the maximum speed is referenced to the encoder.

Maximum speed [pulses/s] =

Rated rpm of the drive [rev/s] x gear ratio x increments per encoder revolution [increments/revolution] x 4

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Example:

Rated rpm of the drive: 3,000 [rpm]

Transmission ratio: 1:1 (no gear)

Increments per encoder revolution: 500 [increments/revolution]

3000 [rpm] = 50 [rev/s]

500 [increments/rev] = 2000 [pulses/rev]

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It is imperative to determine and specify the maximum speed correctly in order to achieve good and reproducible positioning results.

The "Creep/reference run speed" parameter also refers to the encoder. Here, the specified maximum speed is converted into an analog voltage. For

example, let the maximum speed be 10,000 pulses/s, at a creep/reference run speed of 1000 pulses/s. In this case, a voltage of 1 V is output at the analog output.

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The creep/referencing speed must be high enough to keep the drive moving.

You must select a time of sufficient length in the "Monitoring time" parameter to ensure that the drive can supersede the startup holding torque of the axis within the specified time.

Example:

The drive starts moving at an analog voltage of 0.5 V.

Maximum speed: 10000 [pulses/s] = 10 V Acceleration: 1000 [pulses/s²]

-> Speed = 500 pulses/s = 0.5 V

-> T = speed / acceleration = 500 pulses/s / 1000 pulses/s² = 0.5 s

That is, the drive does not start moving until a time of 0.5 s has expired. In this case the monitoring time must be set higher than 0.5 s.

This monitoring time is also used to monitor target approach. That is, the drive must reach the target range within this time, after it has reached the cut-off position.

Use the "Counting direction" parameter to adapt the direction of path monitoring to the direction of movement of the linear axis. Also, take the rotary direction of all transmission elements into account (for example, couplings and gears).

- "Standard" means, the incrementing count pulses correspond to rising actual position values.

- "Inverted" means, the incrementing count pulses correspond to descending actual position values.

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3.5.2 How to Determine SFB Parameters

In the "ACCEL" (acceleration) and "DECEL" (deceleration) parameters, declare the acceleration/deceleration speed values for the drive.

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Example:

At a wanted traversing speed of 10,000 pulses/s and acceleration of 1000 pulses/s², it takes 10 s to reach the speed setpoint of 10000 pulses/s.

The "CHGDIFF_P" (changeover difference in plus direction) and

"CHGDIFF_M" (changeover difference in minus direction) parameters define the changeover position as of which the drive runs at creep speed.

If the difference is set too high, positioning is not optimized over time because creep speed runtime is unnecessarily extended .

The parameters "CUTOFFDIFF_P" (Cut-off difference in plus direction) and

"CUTOFFDIFF_M" (Cut-off difference in minus direction) specify the pulses to go before the drive is switched off at the target approach.

Take into consideration that this distance varies according to the load on the drive.

If you select an insufficiently high difference of changeover/cut-off difference, the drive is switched off at a speed higher than the configured creep speed.

The result is inexact positioning.

The difference of changeover/cut-off difference for the respective direction should at least be proportional to the distance the drive actually requires to reach creep speed. Here, the required traversing speed forms the base. Take the load on the drive into consideration.

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3.5.3 Checking Parameters

Requirements

Your system is wired correctly.

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The positioning submodule is configured, the parameters have been assigned and the project is loaded.

For example, you have loaded the sample program "Analog 1, Getting Started"

which is included in the scope of delivery The CPU is in RUN state

Step What to do 

Verify the wiring 1

• Verify that the outputs are connected correctly

(Analog output and Enable output "CONV_EN" for the converter)

• Verify that the encoder inputs are connected correctly

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S Check the axis motion

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• In "Jog" mode, move into plus and minus direction at creep speed (see module parameters).

The actual sense of direction DIR must correspond with the specified direction.

If this is not the case, change the module parameter "Count direction".

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Synchronize the axis 3

• Select the job "Set reference" (JOB_ID = 1).

Enter the desired coordinate at the actual axis position as JOB_VAL (e. g. 0 pulses).

Execute synchronization by setting JOB_REQ to TRUE.

The coordinate you have specified is shown as actual position value and the synchronization bit SYNC is set.

Evaluate (JOB_STAT) a reported error (JOB_ERR = TRUE).

If required, correct your specified coordinate and repeat the job for setting the reference.

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Step What to do  Check the changeover/cut-off differences

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• In "Absolute/relative incremental approach" mode, approach the specified target (TARGET) that is further away from the actual position than the configured changeover difference.

Here, select a speed (SPEED) that is adapted to your application and higher than creep speed.

Creep speed <= SPEED <= maximum speed.

• Note the individual positioning phases (acceleration, constant run, deceleration, target approach).

Increase the changeover difference to run the drive to the cut-off point at a clearly visible creep speed.

If the configured target range is not reached, reduce the cut-off difference and repeat the run until the target range is reached.

If the configured target range is overrun, increase the cut-off difference and repeat the run until the target range is not overrun anymore.

• Now optimize the changeover difference.

Reduce the changeover difference without changing the cut-off difference and repeat the run.

You can reduce the changeover difference to a point at which the drive just about moves at a hardly visible creep speed, that is, it has actually reached creep speed at the cut-off position and it is switched off there.

Positioning accuracy remains unchanged as long as the drive is switched off at creep speed.

A further reduction of the cut-off difference does not make sense.

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Check the maximum speed (if poor positioning results) 5

• In "Jogging" mode, move into plus and minus direction at maximum speed (see module parameters).

Measure the frequency (e. g., using the counter submodule) of the encoder signal A or B in [1/s]. Multiply the measured frequency byte 4 and enter the product as maximum speed in the module parameters.

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