Glossary · Motion control and drives
Reference switch
Also known as: Home switch, Reference cam
German: Referenzschalter
In motion control, a reference switch is a switch or sensor at a defined position of an axis whose signal the controller uses during homing to establish the axis's reference position, often combined with the index pulse of an encoder for higher repeatability.
- Motion control
In one sentence
A reference switch marks a defined axis position that the controller uses during homing to set the position reference.
Example
The linear axis of a pipetting robot has an inductive reference switch near one end; after power-up it homes to the switch edge and then to the next index pulse.
How it applies
- Engineering: Mechanical switches, inductive or optical sensors serve as reference switches. Their switching-point repeatability, together with the Index pulse, determines how repeatable the reference is.
- Commissioning: The homing method defines which edge of the switch counts and in which direction the axis approaches it. Check that the approach direction is the same every time.
- Operation: A dirty, loose or damaged reference switch shifts the reference; all positions shift with it.
- Documentation: In circuit diagrams and parameter lists, name the reference switch separately from limit switches, and describe how to check the reference after replacing it.
Reference switch vs. limit switch
A reference switch defines a position for Homing and is approached on purpose. A Limit switch marks the end of the permitted travel and should not be reached in normal operation; hitting it stops the axis. Some small systems use one switch for both jobs, which the documentation must state.