ctrlX Drive - Measuring wheel function

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Measuring WheelMeasuring Wheel

This picture describes the use of the measuring wheel function quite well. If the measuring wheel is in contact with the material, the function must be activated in parameter S-0-0520.  If there is no contact between the measuring wheel and the material, then material feed should be carried out via the motor encoder, measuring wheel function itself then is deactivated via parameter S-0-0520. So the motor encoder is used for the positioning when you have no contact of the measuring wheel to the material.

Measuring wheel function - Prerequisites

The following prerequisites are required to use the function :

  • ctrlX DRIVE Runtime >= AXS-V-0316

The following firmware functions must be enabled in order to use the measuring wheel function:

  • Hybrid position control
  • Measuring wheel mode


It also must be possible to connect a measuring wheel encoder to an interface on the drive control unit:

  • Interface for Encoder 2

Measuring wheel function -  Test equipment

I have taken the following measurements and pictures with the listed equipment:

Here is a picture of the experimental setup. As a coupling a rubber ring is used. The rubber ring simulates the material feed. The rubber ring is a very elastic connection. But for the demonstration here quite suitable. Real measuring wheel applications should be much stiffer.


Measuring wheel function - Parameterization
  • Drive using the motor encoder has already been put into operation
  • Now the measuring wheel mode will be parameterized 

Encoder 2 as measuring wheelEncoder 2 as measuring wheel

Feed constant for measuring wheelFeed constant for measuring wheel

Measuring wheel function – Axis mechanics / scaling

If you have done the settings for the measuring wheel encoder then you can select the window „Axis mechanics / scaling“ and you have a good overview about your parameter settings.

Axis mechanics and scalingAxis mechanics and scaling

Measuring wheel function - Drive controlled positioning (example)

Where to find the setting for the parameterization of the filter function:
If you go to your operation mode (here for example the Drive controlled positioning. Then select measuring wheel mode (hybrid position control). Then you see the window “Hybrid position control”.

Drive controlled positioningDrive controlled positioning

Measuring wheel function – Involved parameters
The following parameters are used to parameterize the function
The following parameters are used to parameterize the measuring wheel encoder itself:

Attachment: MeasuringWheelWatchList.jpg as a *.zip to open in ctrlX Drive Engineering

Measuring wheel function - Slip monitoring
Monitoring the slip
  • Due to the measuring wheel mode, slip that can occur between material and drive motor is compensated via the position control. But slip also implies wear in the mechanical drive system and at the material. The controller supports reducing wear by allowing the occurring slip to be monitored with regard to a maximum allowed value to be set.
  • The current actual slip value is displayed in "P‑0‑0242, Current actual slip value". It refers to one measuring wheel revolution, if the "feed constant 2" is active in P‑0‑0185 (typical case: measuring wheel is measuring linear infeed) - or - one revolution of the external encoder, if "feed constant 2" is not active in P‑0‑0185 (encoder is measuring rotary infeed).

  • If the calculated slip exceeds the value in "P‑0‑0244, Monitoring window of slip" (value unequal "0"), the slip monitoring function triggers with the error message "F2036 Excessive position feedback difference" and the drive reacts with the error reaction that has been set.

  • To determine the monitoring window, the maximum occurring slip, e.g. during a machining cycle, is stored in "P‑0‑0243, Maximum occurred actual slip value".
Measuring wheel function - Slip monitoring / current actual slip value

Slip monitoringSlip monitoring

Measuring wheel function – Measurements

Here is a measurement with no active measuring wheel function on the test equipmet. Blue is the actual position value encoder1 and green is the command position value. Violet is the actual position encoder1.

Measurement 1Measurement 1Here the measuring wheel function is activated. Encoder2 is the active encoder for the position regulation. Also the Hybrid position control is activated and the lagless position control is selected. The red signal is the active current slip.

Measurement 2Measurement 2In contrast to the previous measurement, the filter time is increased in here.

Measurement 3Measurement 3Here, as well as on the next slide, the current slip signal is checked using the positions of encoder 1 and ecoder 2. The slip signal is set to zero after one rotation of the measuring wheel. The signal shows then the difference between encoder 1 and encoder 2 in percent.

Measurement 4Measurement 4

Measurement 5Measurement 5

Measuring wheel function - Hybrid position control – Control word control loop

Hybrid position controlHybrid position control

Hybrid position control – Filter time constant

In the following some measurements are shown for a better understanding of the function and the oszilloscope data files have been added to the screenshots. If you want, you can take a closer look at the signals with the oscilloscope function. That's why the oscilloscope files are attached to the screenshots.

Measurement hybrid position controlMeasurement hybrid position controlThe measuring wheel function is activated. The filter time P241 is set to zero.

Hybrid position control 2Hybrid position control 2In contrast to the previous slide, the position control here is with lag.

Hybrid position control 3Hybrid position control 3Here the position loop regulation is lagless. And the filter is set from zero to 300ms.

Hybrid position control 4Hybrid position control 4Here the hybrid position control was switched off.

Hybrid position control 5Hybrid position control 5In this measurement, the filter time is set to the maximum value of 600 milliseconds. Here you can also see the actual position values ​​S51, S53. Specifically the S386 which is a hybrid position of the S51 and S53 and this value is used for the position loop regulation.

Hybrid position control 6Hybrid position control 6In this measurement, the filter time is set to 20 milliseconds. Here you see no great difference between S368 and S53.

Hybrid position control 7Hybrid position control 7Attachement: Some oscilloscope measurement are in the ScopeMeasuringWheel.zip

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