External zero pulse

Valid for S300, S700

General

To increase the accuracy in positioning during a reference run, you can evaluate an external reset pulse. The reset pulse's source is preselected by the parameter REFMODE.

The servo amplifiers S300 / S700 offer two different methods to consider an external zero pulse:

Evaluation of the zero pulse's slope

Whenever a zero pulse's slope is detected, the position is reset (ROFFS); the drive brakes, and drives to the position where the slope has been detected.
The disadvantage of this procedure is that different zero positions are set, depending on how steep the zero pulse's slope is, or how fast the reference run is. As this way of evaluating the reset pulse can be used with analog as well as with digital position transmitters, it is used with all our servo amplifiers

Evaluation of the zero pulse's slope followed by analog positioning

The advantage of this method is that it eliminates the dependence on the reference run speed. The zero pulse only serves as a kind of identification for the sin/cos cycle in which the zero mark is to be positioned. The position of the zero mark within the sin/cos cycle is determined by the parameterizing (parameter REFNOFFS). The disadvantage of this method is that it can only be used with position transmitters with an analog track (sin/cos signal)

The evaluation of the zero pulse followed by analog positioning was implemented in the S300/S700 series starting with the firmware version 2.51 (26.011.2007). By parameterizing REFNOFFS (range 0 ... 360 degrees), the function is activated to a value not equal to 0. The input  REFNOFFS>0 defines the position of the zero pulse within the sin/cos cycle.

Example:

• REFNOFFS = 90 die the zero mark is set at  the zero - crossing of the cos signal (90 degrees = 1/4 of the sin/cos cycle, end of the first quadrant)
• REFNOFFS=360 the zero mark is set at the maximum amplitude of the cos signal (360 degrees = 0 degrees = beginning of the sin/cos cycle).

With REFNOFFS=0 exclusively the evaluation of the zero pulse's slope is activated . Thus method  number 1 is active (default adjustment).

As the slope of the hardware's zero pulse only serves as a marker for the sin/cos cycle, it is problematic if the distance between the hardware's zero pulse and the analog position REFNOFFS is situated near 180 degrees.

In this case it is possible that due to the scanning jitter of the zero pulse's slope two different zero points are contacted. In this case the distance between these two positions is exactly the length of a sin/cos cycle. This problem can only be solved by changing the REFNOFFS adjustment.  This parameter should be adjusted thus that the distance between the physical zero mark and the "analog" zero position is less than or equal to 90 degrees.

To facilitate this adjustment, the variable REFNPOS was implemented. This variable indicates the position of the hardware's zero pulse to the user (indication in degrees), and is set again after every reference run.

Starting

1. To activate the function, adjust the parameter REFNOFFS to 90 degrees.
2. Now. start the reference run.
3. Now, read out the REFNPOS value, and calculate the difference to REFNOFFS (90 DEGREES) .  If this difference is smaller than +/- 90 degrees, the procedure is finished. Otherwise the value for REFNOFFS should be adjusted to the REFNPOS value.
4. Finally, press SAVE to save all adjustments.

To better understand the functioning of the search for the anlog zero point, in the following the process is described in detail:

1. The reference run is started at the speed VREF/VREF0 .
2. When recognizing the zero pulse's slope  (REFMODE) the beginning of the current sin/cos cycle is calculated, and the position of the hardware's zero pulse is latched (variable REFNPOS).
3. PFB, the current position of the position control, is set to the absolute sin/cos position (PHI_ENC) .
4. The drive brakes to 0 speed.
5. Automatically, a motion task is started to the REFNOFFS position.

When the referencing is completed, the drive says  ROFFS. This position matches exactly the position within a sin/cos cycle that has been specified by the parameter REFNOFFS. To check this, the variable COENC can be recorded corresponding to the amplitude of the analog cos signal. Disregarding the oscillation of the analog signal, after referencing this value should show 0 (with  REFNOFFS adjusted to  90 degrees). When reflecting on the actual PFB position, you should also consider the current contouring error (PE).

Some advice concerning the recording of the scope

To verify that the zero destination can be repeated, you should perform several recordings with the following variables:

• PFBL –  actual position at 64 bit 
• PHI_ENC – actual position at 32 bit Istposition within a turn (within a polepitch).
• COENC – amplitude value of the cos signal
• PE – current contour value

The recordings should always  be effected at the end of a reference run (DIRECTLY as triggers) after the final stage has been enabled. The results of the recordings should be stored as EXCEL files.

Resolution of the position detection

1. 1 turn (1 pole pitch distance) is resoluted by  ENCLINES sin/cos cycles. The current positon within a pole pitch can be extracted via the variable PHI_ENC  (32 bit/pole pitch).
2. Sin/Cos oscillations are acquired the analog way, and are deposited as 16 bit values in the SIENC/COENC variable The resolution is 1350 Counts/ 1 volt.

This results in the following maximum resolution (for a 1 volt signal):

1 POLEPITCH = 4*1350*ENCLINES Counts

Regardless of the adjusted ENCLINES, the internal resolution always is either  32 Bit / turn, or 32 Bit / polepitch.

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