CNC Router Control GuidelinesBy Youssef Edward
April 6, 2019
CNC router building has three steps: first building the mechanical infrastructure, making the electrical control for the whole machining, and finally doing the proper programming for special purpose machining. Here is considered the part of electrical control of the machine.
Generally CNC router is complex machine that consist of many elements under control of the main computer. The computer or generally, the controller, sends electronic signals to the interface unit which distributes it to the driver units that feed many units in the machine. Those units could be mandatory or optional. The mandatory units are:
- The motors that do the motion for the machine.
- The motor spindle that do the drilling and engraving.
The optional units are such as :
- The oiling units
- The Vacuum unit.
- The Tool Changer.
Each of those units needs one or more cards for driving them. We focus here on the mandatory units which are the motors and spindles.
The motors used for motion may be stepper motors or servo motors. Each type has its own driver to operate properly. Stepper motors are the cheapest and simplest in design. Servo motors are more expensive and more complicated then stepper motors. The benefit of servo motors is that every command it receives from the controller is feedback by a mini-control circuit inside the motor. This increases the reliability for the motor. On the contrast, stepper motors ( also called open loop motors) takes the command but send no feedback to the computer. If there is abnormal condition which halts the motor, the computer will not be advised.
The spindle is three phase motor that takes three lines of 220 V AC sine wave signals. The driver for this motor is three phase inverter that is available in the market. The inverter may take two phase 220 V or three phase 380 V AC. The inverter is generally computer based that run under the control of micro-processor. It is programmed using keys on the panel of the device. Some of the programmable features are such as:
- Acceleration of the rotation. Generally, it is ramping in nature.
- De-Acceleration of the rotation.
- Maximum rotation speed.
- Start signal of execution. It may be using button on panel or by contact of two pins on Rozet.
A block diagram is shown below for the basic control of the CNC router.
The Interface unit is a card that takes low power signal directly from the computer and distributes them to power cards. The link between this card and the computer may be via USB or printer port.