Encoders and actual values

Interface

The encoder parameters are accessed via the System Manager.

Determining actual values: determining the direction (encoder polarity)

Without correctly determining the actual value, an axis is "blind", and cannot behave in a coordinated manner. Commissioning, therefore, must begin here. This requires two items of information to be found or checked: the direction of the counting, and the value of the increment.

1. Determine or specify which direction of the axis movement is to be considered "positive", "rising", or "upwards". When moving in this direction, the actual value acquisition system must report rising values.
2. If you can disconnect the drive electrically and to move the axis manually, turn the drive in such a way that the machine, for instance, moves in the "positive" direction, and observe the display of the actual value in the online image of the axis.
3. If this is not possible, it will be necessary for you to turn the axis using the drive. This means that you will be starting operation of an axis that has not been parameterized. Special care is required because this procedure will disable all the controls and monitors. The axis will be operated with nothing but the feed forward and fictional data. Proceed as follows:
• If it is possible to separate the load from the drive (e.g. by removing belts or other transmission media) without disconnecting the encoder at the same time, this is undoubtedly what you should do!
• On the controller's global tab, set a value of 1.0 for the feed forward weighting.
• If the controller has a PID tab, set the position control factor Kp (and all other control factors) to zero. Deactivate the automatic offset adjustment.
• On the drive's global tab, adjust the output limit to +0.1 or -0.1.
• If the drive has an analog tab, set the reference speed to a fictional value (not too small) and set the reference output to 1.0. Set the drift compensation to zero.
• On the global tab for the axis, set the same value for the maximum permitted speed as for the drive's reference speed. Set one tenth of the same value under manual speed max and manual speed min. Deactivate all the end position monitors, following error monitors and other checks.
• Make sure that there is nobody in the hazardous area.
• Using extreme care (with your hand by the emergency off switch) switch the axis on electrically. There should not be any drift movement.
• Now use the <F2> and <F3> keys in the online image of the axis to move in the "smaller" and "larger" directions, and observe the machine. If, when the <F2> key is pressed the machine moves in the "larger" direction, and when the <F3> key is pressed it moves in the "smaller" direction, alter the motor polarity on the drive's global tab, and repeat this step.
• Now compare the direction of the machine's movement with the counting direction of the actual position display in the online image.
4. If the counting direction is supposed to the specified movement direction, change the inverse transducer counting direction (polarity) parameter on the encoder's global tab. Then you should remove all current from the drive and reset the axis in the online image <F8>.

Determining actual values: increment evaluation (scaling)

After the drive's counting direction has been determined, it is necessary to set the value of the increment. This value is to be set in the scaling factor on the encoder's global tab.

1. The value can be calculated if the feed rate per rotation and the number of increments (not the number of impulses!) are known. Nevertheless, you should check the value as follows.
2. If you still do not know any value for the increment, at least set an estimated value. If you have no information at all about the value to be set, select a fictional value such as 0.01 mm.
3. If you are performing a check later, then of course you start with values that have been determined beforehand.
4. It is now necessary to travel over a known distance as a test movement (as in the determination of direction). The correct value is now calculated from the currently set scaling factor multiplied by the actual travel divided by the indicated travel.

Determining actual values: zero offset shift

This section is only to be carried out for absolute encoders.
In incremental systems at this point you should set the actual value to a reasonable figure (with the drive switched off and followed by a reset through <F8> in the online image for the axis). You will find the input boxes and function keys for this purpose on the function tab for the axis. Enter the value 0 for the zero correction. To adjust the axis measurement system to the machine, the calibration function of these encoders is used, the parameters for which will be determined at a later stage.

1. Determine the position of the axis within the machine. The rules for this cannot be generally stated and can only be specified by the machine constructor. In many cases, the distance of a reference point on the moving part of the machine to a reference point on the fixed part of the machine body is chosen.
2. If it is not possible to determine the position in this way with the necessary precision, make a preliminary adjustment, and repeat this step again later.
3. Find the difference between the determined position and the displayed position and enter this with the opposite arithmetic sign in the zero-offset shift of the encoder's global tab. If a value has already been entered there, modify the existing value by adding the new value to it. If (when repeating this step later) the position control is already active, you should electrically halt the drive and reset the axis before switching on again <F8>.
4. Example: The position is determined to be 752.0 mm, while the displayed position is 1983.52 mm. The difference, in other words, is 1231.52 mm. If no value has yet been entered in the zero-offset shift, you can simply enter -1231.52. If a zero offset has already been entered, add the new value to it. In this example, an existing value of +150.0 would yield the new value -1081.52 mm.

Further encoder parameters

The encoders offer a range of working modes for optional setting. These include, for instance, determination of the actual speed or of the actual acceleration. If necessary, these measurements can be activated on the encoder's global tab. If these values are not interesting, they should be specifically deselected, since determination of the values increases the real-time loading.
It is also possible to set a modulo factor. This is of particular interest for rotating axes, since it allows the relative position within one rotation and the number of rotations to be found automatically.

Finally, the encoder values (position, speed, acceleration) can be filtered, which is of particular significance for encoder axes.