Development of FPGA-based module of three-phase spindle motor speed-controller for CNC PCB milling and drilling machine

Abstract

Motor spindle (three-phase asynchronous AC motor) is one of important components of Computer Numerical Control (CNC) Printed Circuit Board (PCB) milling and drilling machine. This motor can engrave copper layer to form circuit paths and drill holes to fit electronic components of the circuit. To perform engraving process, the speed of the spindle motor should be regulated according to PCB material used. This paper discusses development of Field Programmable Gate Array (FPGA)-based three-phase spindle motor speed control module. This module uses fixed Voltage/Frequency (V/F) control method that is implemented by Sinusoidal Pulse Width Modulation (SPWM) technique so that maximum torque of the motor can be kept constant and harmonic signals can be suppressed. This module consists of a digital controller implemented in an FPGA and a three-phase, full-bridge inverter circuit. The FPGA controller generates digital SPWM signals sent to the inverter. This circuit converts DC voltage to three-phase AC voltage with certain frequency according to the input. This module has a capability to control the rotational speed of the spindle motor in the range of 14000–28000 RPM. This corresponds to input frequencies in the range of 250–500 Hz with fixed V/F and Speed/Frequency (N/F) ratio. The acceleration and deceleration are accomplished using a ramp function so that the starting torque of the motor is not reduced at high input frequencies.