Manual Pulse Generator (MPG) Basics for CNC Machines

A CNC machine manual pulse generator (MPG) is a handheld device used in conjunction with computer numerical control (CNC) machines. It serves as an input device for controlling and fine-tuning the movement of the machine's axes, typically used for tasks like jog movements, homing, and setting workpiece offsets. The operator or machinist can use the MPG to manually control the machine's position with precision.

Key features and functions of a CNC machine manual pulse generator include:

Handheld Device: An MPG is a compact, handheld device that the operator can hold and use comfortably. It typically has a rotary wheel or knob, along with buttons or switches for various functions.

Rotary Encoder: The main control element of the MPG is a rotary encoder, built into a detented handwheel that can be turned in both directions. The rotary encoder generates pulses based on the direction and speed of rotation.

Incremental Motion Control: When the operator rotates the MPG's knob, it sends incremental movement commands to the CNC machine's control system. The number of pulses generated corresponds to the degree of movement in the desired direction.

Precision Adjustment: An MPG allows for very fine adjustments and control of the machine's position. This level of precision is especially useful for setting work offsets, aligning tools, or manually moving the machine during setup.

Homing and Jogging: An MPG can be used to bring axes close to a reference position before homing, and for jogging, which involves manually moving the machine's axes to position them accurately.

Axis Selection: The device often has buttons or switches to select the specific machine axis (e.g., X, Y, Z) that the operator wants to control.

Function Buttons: In addition to axis selection, an MPG may include function buttons for purposes such as zeroing the position, setting offsets, or other specific machine functions.

Emergency Stop: Some MPGs incorporate an emergency stop button to halt machine movement in case of an emergency or to ensure operator safety.

CNC machine manual pulse generators are particularly valuable in situations where precise control and fine adjustments are required, such as during setup, tool changes, or diagnostic procedures. They provide a tactile and ergonomic means for operators to interact with CNC machines, reducing the need to input commands through a computer or control panel and enhancing the overall usability of the CNC system.

MPG Signal Types and Compatibility

An MPG is a small rotary encoder. It sends two pulse trains, A and B, 90 degrees apart, so the control can tell the direction of rotation. Many MPGs give 100 pulses per revolution, one per detent, and the control multiplies each pulse by the selected step (for example x1, x10 or x100).

To be compatible, a replacement must match:

• Supply voltage: commonly 5 V DC, with 12 V and 24 V versions also available.
• Output type: line driver (differential A, A-, B, B-), voltage output or open collector.
• Pulses per revolution: must match what the control expects.
• Form: panel-mounted handwheel, or a handheld pendant with axis and step selector switches and, on some models, an enable or emergency stop switch.
• Connector and cable: number of cores, connector type and cable length.

Common MPG Faults and Checks

• Axis does not move: confirm the control is in handle mode and the correct axis is selected. Then check supply voltage at the MPG.
• Axis moves only one way or jumps: usually one channel (A or B) is lost because of a broken core or bad connector.
• Movement is erratic: check for a damaged pendant cable, a loose shield or electrical noise from nearby motor cables.
• Wrong step size: the multiplier switch may be faulty or a parameter may have been changed.
• Stiff or loose wheel: worn bearings or detent mechanism. Replacement is usually more practical than repair.

Pendant cables flex constantly, so they and their connectors are the most common failure point. EKA CNC supplies manual pulse generators for CNC machines.

Frequently Asked Questions