Limit Switch

Introduction

A limit switch is an electromechanical device used to detect the physical position or movement limit of a machine part. In CNC and laser engraving machines, limit switches are essential for safety, accuracy, and automated homing. They allow the controller to know when an axis has reached its maximum or minimum position.

Types of Limit Switches

• Mechanical Lever Switch: Uses a metal arm or roller that is pressed when the axis reaches its end.
• Micro Switch: Compact switch with high reliability and fast response.
• Optical Limit Switch: Uses infrared light to detect movement without physical contact.
• Hall Effect Switch: Detects magnetic fields for contactless sensing.

Working Principle

Limit switches work by changing their electrical state when they are physically triggered by a moving part of the machine:

• When the axis moves, it presses the switch lever or sensor.
• The internal contacts open or close, sending a signal to the controller.
• The controller immediately stops movement or sets the axis position.

Electrical Components

• Common (COM): Shared connection point.
• Normally Open (NO): Circuit closes only when the switch is pressed.
• Normally Closed (NC): Circuit opens when the switch is pressed.
• Housing: Plastic or metal casing for protection.
• Actuator: Lever, roller, or button that gets pressed.

Why Limit Switches Are Important

• Prevents motors from over-traveling and damaging the frame.
• Allows automatic homing of X, Y, and Z axes.
• Improves repeatability and positioning accuracy.
• Provides an emergency stop reference point.

Connection with MKS Board

Limit switches are connected to the MKS controller board using signal and ground pins:

• The Signal pin detects switch activation.
• The Ground pin completes the circuit.
• Most setups use Normally Closed (NC) wiring for safety.
• Firmware detects the trigger and stops axis movement instantly.

Applications

• CNC machine homing systems.
• Laser engraver axis limits.
• 3D printers and robotic arms.
• Industrial automation and safety systems.

Advantages

• Simple and reliable operation.
• Low cost and easy installation.
• Improves machine safety.
• Compatible with most CNC controllers.

Limitations

• Mechanical wear over time.
• Requires precise mounting alignment.
• Physical contact types may need maintenance.

Safety & Maintenance

• Secure mounting to avoid false triggers.
• Check wiring connections regularly.
• Keep switches clean from dust and debris.
• Test homing function after installation.