The core function of pulse signals: Positioning and speed control
Pulse signals are position commands received by the servo drive. Their quantity and frequency directly determine the motor's displacement and operating speed.
Pulse quantity → Target position (displacement)
The servo drive internally counts the total number of received pulses (i.e., "pulse accumulation value") and converts it into actual mechanical displacement based on the electronic gear ratio.
Electronic gear ratio: This is an adjustment parameter for the pulse equivalent (such as numerator/denominator setting), used to match the ratio of the pulse signal to the mechanical displacement. For example:
If the electronic gear ratio is 1:1, and the servo motor corresponds to 2500 lines of encoder feedback per revolution (i.e., 10000 pulses per revolution, 4x frequency), then 1 pulse = 1/10000 of a motor revolution.
If the mechanical transmission ratio is a lead screw pitch of 10mm/revolution, then 1 pulse corresponds to a lead screw movement of: (1/10000) revolutions × 10mm/revolution = 0.001mm (i.e., 1μm pulse equivalent).
Application Scenarios: By sending a fixed number of pulses, a servo motor can precisely move to a target position (e.g., positioning in a dispensing machine, coordinate movement in a CNC machine tool).
Pulse Frequency → Operating Speed
The frequency of the pulse signal (unit: Hz or kHz) determines the motor's rotational speed. The higher the frequency, the faster the motor rotates.
Formula: Motor speed (r/min) = (Pulse frequency × 60) / (Encoder lines × 4 × Electronic gear ratio denominator).
(Note: "×4" indicates a 4x frequency multiplication by the encoder, counting both AB phase edges of the quadrature pulses; the electronic gear ratio denominator affects the pulse equivalent.)
Application Scenarios: By adjusting the pulse frequency, acceleration, deceleration, or constant speed movement of the motor can be achieved (e.g., speed control of a conveyor belt).
Core Function of the Direction Signal: Controlling Forward and Reverse Rotation
The direction signal is a switching quantity (high/low level) used to tell the servo driver whether the motor should rotate in the forward or reverse direction.
Signal Logic
The level state of the direction signal (e.g., high/low) is associated with the motor's direction of rotation. The specific logic is set by the driver parameters (configurable as "high level forward rotation" or "low level forward rotation").
For example: if "high level forward rotation" is set, the motor rotates forward when the direction signal is high and reverses when it is low.
Coordination with Pulses
Even if only a single-direction pulse is sent (e.g., a continuous positive pulse), the motor will only move in one direction. For bidirectional movement, the motor direction must be switched using the direction signal, and the number of pulses must be coordinated to achieve different positioning positions.
Typical Applications: Automatic reciprocating motion (e.g., the left-right swing of a robotic arm, alternating X/Y axis movement of an XY platform).
Typical Control Scenarios of Pulse + Direction Mode
This control method, due to its simple structure and low cost (requiring only two signal lines: pulse and direction), is widely used in single-axis or multi-axis independent control scenarios:
Jog Control
The direction signal is triggered by an external button (such as a PLC I/O point), while simultaneously outputting a low-frequency pulse (or maintaining pulse output via a button), enabling manual low-speed movement of the motor (e.g., fine-tuning during debugging).
Positioning Control
The PLC or motion controller calculates the number of pulses for the target position (converted based on the electronic gear ratio), sends the corresponding number of pulses + direction signals, and the driver controls the motor to precisely reach the target point (e.g., the material handling position of a packaging machine, the placement coordinates of a pick-and-place machine).
Speed Control
If precise positioning is not required, and only constant speed operation is needed, continuous pulses (fixed frequency) can be sent, and the direction signal determines the direction of rotation (e.g., continuous operation of a conveyor belt).
Comparison with Other Control Methods
Compared to bus control (such as EtherCAT, CANopen) or analog control (±10V speed commands), the pulse + direction mode has the following advantages:
Simple Hardware: Only two signal lines (pulse, direction) + enable signal (EN) are required, resulting in low cost.
Strong Anti-interference: The pulse signal is a digital quantity (differential or open collector), making it less susceptible to electromagnetic interference (especially in short-distance scenarios).
High Real-Time Performance: No complex communication protocols are required; commands are directly written to the driver, resulting in fast response.
