What’s a “Limit Switch”?
A limit switch is a device used to control the movement of mechanical parts. Dental CNC machines use several of these switches to operate various sub-assemblies. They are found in each machine axis, tool measurement probe, and safety interlocks. Limit switches are used to “tell” the machine’s control system where a component is relative to other parts of the machine. They are an integral part of your machine’s motion control system.
Interesting Details about “Limit Switch”:
How does it work?
Limit switches have two components: an actuator (usually a button or metal arm) and a set of contacts. When a part of the machine comes in contact with the actuator, the switch makes or breaks an electrical circuit which sends a signal to the machine’s control board. When the board receives the signal, it carries out a pre-set action.
Most of the limit switches found in our machines are used in each of the machine’s axes. Each axis assembly has at least one. The “home” switch is located at the beginning of the axis range of motion. When a machine first turns on it goes through a homing sequence where it finds the limit switches on each axis. Once the machine is homed, it knows where each axis is in space. This location is critical, as all machine g-code commands are referenced from the home position.
Tool measurement probes
Many of the Tool measurement probes used in dental machines also utilize a limit switch. It’s a cost-effective way to measure tools, and the system works with enough accuracy for dental applications.
One more area you may find these switches is inside your machine’s safety interlock system. Typically, there will be one or more switches employed in the circuit that tells the machine if the milling chamber door is open or closed.
Normally closed or normally open?
Switches can be wired to either open an electrical circuit or close an electrical circuit. If the switch is setup to open a circuit on contact it is considered “normally closed”, meaning that its default position is closed. If it’s setup to close a circuit on contact, it is “normally open”. This arrangement depends on the design of the machine.
Thanks for reading! We hope this break down of the term “Limit Switch” has been of value. Stay tuned next week for another post like this!
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