RoboteQ AX3500 user manual Voltage Levels, Thresholds and Limit Switches

Voltage Levels, Thresholds and Limit Switches

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 87.

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 fixed 2.5V 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.

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 52 and Figure 51 show the conditioned signals as seen by the encoder.

In Figure 52, 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.

Signal on Channel A or B

Quadrature Signal

Switch Detect Signal (Not meaningful)

FIGURE 51. Signals seen by encoder using direct connection and no limit switches

2.5V

0.5V

In Figure 51, the encoder and switches are wired to the encoder module using a set of resistors designed to create a multi-level signal combining both pieces of information. Details on the necessary wiring is provided in the next section.

Since the encoder output signal is “shifted-up” by a few volts, it always stays above the Limit Switch comparator’s threshold, and no Switch Detection condition is generated. However, since the limit switches connect to ground when On, the level will dip below the 0.5V and generate a Switch Detection condition.

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