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SAMLight Manual > Option MOTF > Encoder Signals

Encoder Signals
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The flow chart in figure 350 shows the general MOTF hardware setup with encoder signals.

MOTF_FlowChart_Hardware_Setup

Figure 350: Flow Chart MOTF hardware setup

warning

Verify the GND connection between the USC/RTC card and the encoder to adjust the level. To avoid noisy signals use short cables and check the power supply of the encoder.

The USC cards are designed to handle two 90° shifted encoder signals (track A and track B) delivered by standard commercial encoders. The USC decoder interprets each transition, whether the count impulse is on track A or track B of the respective channel. The interpreted belt direction depends on the phase shift between both tracks (see figure 351).

Phase shift B after A:

If the phase shift between track A and track B is + 90° (refer to figure 351, upper part), the belt is interpreted as moving in the default direction (let's call it forward). In this case, the encoder counts positive which is necessary for advanced MOTF features (like ScMotfOffset). Each falling or rising edge of track A or track B will increment the encoder counter by + 1. That means each track period T will lead to 4 encoder counts in total.

Phase shift B before A:

If the phase shift between track A and track B is - 90° (refer to figure 351, lower part), the belt is interpreted as moving in the non-default direction (let's call it backward). In this case, the encoder counts negative. Each falling or rising edge of track A or track B will increment the encoder counter by - 1. That means each track period T will lead to - 4 encoder counts in total. Please note that for the encoder counting negative, the ScMotfOffset entity will not work properly.

 
To change the counting direction, the signals of track A and track B can be swapped either by changing the wiring of the tracks or by using Swap A/B in the software. The direction of MOTF compensation may need to be adjusted as well after changing the direction of the encoder counter. Please refer to the corresponding hardware specific sub-chapters for further information.

MOTF_encoder

Figure 351: Encoder signals (single ended). Note that each period T consists of 4 encoder counts.

Using encoder signals, it is necessary to specify the conversion between the counts of the encoder and the corresponding distance on the work piece. This conversion is given by the MOTF multiplier in combination with the optic settings.

 

note

The amplitude of the encoder signals should be in the range of 2.5 V to 5.0 V. The signals should be as low-noisy as possible, since noise could be interpreted as additional pulses. Possibly, you can use a differential encoder and MOTF_CH1 (40-pin connector).

In case of problems, verify the switching threshold levels (cut-off frequency see USC-1, USC-2, USC-3) of the encoder signals with an oscilloscope and/or use differential signals.