Quadrature with Stepper Output Overview

The STEP interface module is one of two RMC interface modules with an interface for quadrature encoder feedback. This module provides stepper drive output, while the QUAD interface module provides analog drive output. Together, these modules allow the RMC100 series motion controllers to control a wide range of motors and linear actuators with quadrature encoder feedback. For details on the QUAD module, see Quadrature with Analog Output Overview.

Each stepper module can control two stepper axes, each with both stepper-motor and quadrature-encoder interfaces.

The quadrature-encoder interface does not have to be used; the motor can be controlled in open loop and still take advantage of the RMC’s host of target generating methods including trapezoidal and s-curve point-to-point moves, gearing, synchronization, and splines.

When used with quadrature feedback, faults can be triggered on following errors, and motor compensation can be enabled. See Stepper Compensation for details on this feature.

Features

Two Complete Axes per Module. Each includes the following:

Stepper Motor Interface:

1 MHz Maximum Output Frequency
Step Output
Direction Output
Drive Enable Output
Drive Fault Input

Quadrature Encoder Interface:

4,000,000 counts/second Maximum Encoder Rate
A and B Inputs
Index Input with High-speed 63hs Position Latch

Additional Inputs:

Extend (CW) Travel Limit Input
Retract (CCW) Travel Limit Input
Home Input with High-speed 50µs Position Latch

Status LED

Digital Noise Filters on All Inputs
All Discrete Inputs are Isolated
Control in Open or Closed Loop (with or without quadrature interface)

Step and Direction Outputs

Each axis has two outputs for controlling the stepper motor movement. These are the Step and Direction signals that connect to the stepper drive. The Step signal carries a series of pulses that tell the drive how many steps (or microsteps) the motor should move. The Direction signal controls the direction the motor moves. Both of these signals are generated by differential line drivers.

Drive Enable Output

This output to the drive allows the RMC to turn off the drive using the Amp Enable/Disable command. The enable output (labeled ENABLE + and -) is a solid state relay that is closed when enabled or active.

Vcc Output

This is a nominal 5 V output that can be used in conjunction with the Step, Direction, and Enable outputs to interface drives that require a positive common input. See Stepper Wiring for details.

Note: DO NOT use this output to power encoders.

Drive Fault Input

FAULT + and - is an input from the drive or some other source that can be set up to trigger the RMC to stop its target generator and stop generating step pulses. The user can select the active state of this input by the Fault Active State bit in the axis’s Config word; by default the RMC is set-up to fault when current stops flowing through the input. This way the axis will fault on loss of control power. Bit 15 of the Status word is set if a Fault or Encoder error has occurred. The Auto Stop parameter determines how the axis will stop when a fault occurs.

Quadrature Encoder Inputs

The RMC stepper module accepts signals from quadrature encoders. The A and B signals from the encoder are decoded to generate a positive or negative count; the count is then used to monitor the axis position. Each signal from the encoder is received into a differential line receiver for compatibility with differential line driver encoders. The negative input is biased so some encoders with open collector or TTL outputs can also be used, though this is not recommended due to the possibility of electrical noise.

Index (Z) Input

The index input is active for one count of each quadrature encoder revolution. It is used to qualify or narrow the effective width of the home input to make the homing more repeatable; see Homing a Quadrature Axis for details. The user may change the active state of this input by changing the Home Active State bit in the axis’s Config word.

Home (H) Input

This input may be used in homing the system; see Homing a Quadrature Axis for details. This input will be connected to a normally-off proximity switch. The user may change the active state of this input by changing the Home Active State bit in the axis’s Config word.

Extend and Retract Travel Limit Inputs

The Extend Limit (CW) and Retract Limit (CCW) switch inputs tell the RMC that a travel limit has been reached and can be configured to automatically halt the axis. By default the limit switches are considered inactive when enough current is flowing through the RMC inputs. This way the limit switches will look active to the RMC if control power is lost. The user may change the active state by setting the Limit Switch Active State bit in the axis’s Config word.

The Auto Stop bits must be set to automatically stop the axis based on these limit inputs.

Note: There is only one bit in the Config word for both limit switches so both limit switches must have the same active state.

If a limit switch is not used it should be wired in the inactive state or the Limit Switch Active State bit must be configured to disable the inputs.

Motor Position Compensation

When quadrature encoder feedback is used, the RMC may be configured to compensate for differences between the target and actual position of the motor. See Stepper Compensation for details.