Many German serial encoders (mainly SICK Stegmann Hiperface and Heidenhain EnDat) use incremental sine wave signals in addition to the serial data lines. It is important to check that these signals are outputting correctly and with proper amplitude values. Excessive noise or improper amplitudes can cause major problems on the drive.
This becomes especially important on inductive encoders (Heidenhain EQI/ECI, SICK Stegmann SEL/SEK Series encoders, among others) on which the alignment directly affects the signal amplitudes and may cause alarms if not set correctly.
Line Level Test
Encoders with these 1Vpp signals will require the use of an adapter module for Mitchell systems to read their values properly.
- Encoders rated for 5VDC will use the TI-5101 adapter module, make sure to set both dip-switches on the module to OPEN (OFF).
- Encoders rated for 7-14VDC will use the TI-5104 adapter module.
All Heidenhain EnDat encoders will require a 120Ω resistor placed between A+ and A- (pins 3 and 4 on J1) and B+ and B- (pins 5 and 6 on J1). These resistors can be added to the test cable screw-in terminals as shown in the picture below, or directly to the module itself.
On the Line Levels test, rotate the encoder slowly by hand and check that the VecLev field is green all around the turn. The VecLev provides a comparative value for both A and B incremental channels. If the incremental amplitude is poor quality or not outputting on either channel, the VecLev field should indicate with a red color to highlight the issue. If needed, you can reset the max and min values with the "Reset Max/Min Values" on the left.
While performing this test, is normal to momentarily get a red box on the Rot Speed field, as it cannot read the amplitudes that quickly, but it should go back to green once the shaft has stopped turning.
Incremental Count test
The Count Test button provided on these encoders selection is counting the absolute serial track, not the incremental signals that have A and B sine wave outputs (labeled as SIN and COS). This makes performing a proper count on these signals more difficult as there is no index pulse. The INCREMENTAL field displays the counting of the incremental A/B signals. They will count up or down depending on the direction of rotation. Data Display also has a 'Zero count' button which clears this field to 0. The following tests can help to determine the true incremental counts per revolution of the encoder:
- Serial Encoder Absolute Position Count Test: Keep the shaft stationary and record the SER POS COUNT (absolute serial position) value, then press the Zero count button. Now rotate the shaft one full turn, stopping at the exact same SER POS COUNT value. The resulting number on the INCREMENTAL field will be the counts/rev of the incremental tracks.
- Static Lockup Count Test: Lockup the motor with +U-V, then click the Zero count button. Make a full rotation and re-lock the motor into the same +U-V position. The resulting count on the INCREMENTAL field should be close to the true counts/rev value. Increase accuracy by doing 10 turns and dividing the resulting count by 10.
- Reference Mark Count Test: Make a reference mark on both the shaft and the motor frame, click the Zero count. Make one rotation and try to come back as close to your mark as possible. Increase accuracy by doing 10 turns and dividing the resulting count by 10.
Adjusting the scanning gap on inductive encoders
Inductive encoders are typically a two-piece setup consisting of a bearing-less encoder wheel mounted to the encoder shaft and the scanning head located on the body of the encoder. The amplitude of the
feedback signals is altered by the distance of the encoder wheel relative to the scanning head. This
spacing is referred to as the scanning gap.
There are many different types of inductive encoder mountings, and the scanning gap adjustment
method will be slightly different for each type. However, the general theory remains the same:
Adjust the position of the encoder body closer or farther away from the encoder wheel until the Line Level voltages get in the green.
- Stegmann Hiperface encoders can be electronically aligned after the scanning gap is set.
- Heidenhain EnDat encoders will require some switching back and forth between Data Display to see the alignment angles and Line Levels to check the scanning gap until the encoder position is finally set. The encoder will likely show alarms in Data Display during the adjustment process. Simply click “Reset Alarms” to make sure that they do not return after the proper adjustment has been made.
Heidenhain EQI/ECI 1300 series encoders (See video above).
In this setup, the encoder is tightened down to the motor shaft with a 5mm center bolt (only to be removed to take the encoder out), while a "cam" style 3mm bolt holds the alignment and position in place (shown with an arrow).
Once both Line Level and Alignment angle are correct tighten the “cam” style 3mm bolt head. The thicker part of the bolt head will force the encoder body into a locked position, setting the scanning gap and alignment.
Heidenhain EQI/ECI 1100 series encoders.
On this setup, the red arrows show the 3mm screw that ties the encoder to the motor shaft and the green arrow shows another 2mm set screw that adjusts the alignment position and scanning gap (this also must be removed to take the encoder out of the motor).
Once the scanning gap and alignment angles are correct, simply tighten the set screw (green arrow) to lock the settings. The large 8mm threads in the center hold down the encoder’s wire retention cap. You can use an 8mm bolt in these threads to aid with adjusting the encoder position.