RoboteQ Dual Channel Digital Motor Controller AX2550 - Manual (Page 72)

Installing, Connecting and Using the Encoder Mod-
72 AX1500 Motor Controller User’s Manual Version 1.9b. June 1, 2007
Important Warning
Excessive cable length will cause electrical noise to be captured by the controller and
cause erratic functioning that may lead to failure. In such situation, stop operation
immediately.
Motor - Encoder Polarity Matching
When using the Encoder module for closed loop speed control, it is imperative that when
the motor is turning in the forward direction, the counter increments its value and a posi-
tive speed value is measured.
Using the PC utility, it is possible to exercise the motors and view the encoder readings.
See “Encoder Testing and Setting Using the PC Utility” on page 79.
If the Encoder counts backwards when the motor moves forward, correct this by either:
1- Swapping Channel A and Channel B on the encoder connector. This will cause the
encoder module to reverse the count direction, or
2- Swapping the leads on the motor. This will cause the motor to rotate in the opposite
direction.
Voltage Levels, Thresholds and Limit Switches
The encoder module’s input uses a comparator to reshape the encoder’s output signal. If
the signal is below a programmable threshold level, then it is considered to be 0. If above,
it is considered to be 1. The output of this comparator feeds the quadrature detector and
counters.
On the Encoder module, the threshold voltage may be changed under software control to
any value between 0 and 5V in order to meet unusual encoder specifications. By default,
the threshold level is 2.5V.
Another set of comparators on the same input signals detects pulses that are above and
below a fixed 0.5V threshold. Using a special circuitry for creating multi-level signaling (see
next section below), the output of these comparators serves to detect the status of
optional limit switches.
Figure 43 and Figure 42 show the conditioned signals as seen by the encoder.
In Figure 43, the encoders are connected directly to the Channel A and B inputs. In this
case, it will cause a Switch Detection condition because the encoder’s 0 level is below
0.5V, which should be ignored.