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Session 3648

Microprocessor Controlled Milling Machine: A Student Project

Mohammad Fotouhi, Ali Eydgahi, Joshua Wagner University of Maryland Eastern Shore

Abstract

This paper describes the details of an undergraduate design project in our Design Technology course and the experience gain by the student involved. The intent of the course is to expose students to real world design projects. Students are expected to be creative and innovative in their design projects and utilize a multitude of engineering disciplines that Engineering Technology Program offers at the University of Maryland Eastern Shore. The objective of this project was to use a 68HC12 Motorola micro- controller to control a three-axis motion of a milling machine. This micro-controller was chosen because it has multiple inputs/outputs, built in 8-bit analog to digital converter and timer, pulse width modulator, 16 bit I/O bus, and on board flash memory. In this project, student designed an interfaced circuit to micro-controller and wrote a program in assembly language to control the motion of each stepper motor that is responsible for each axial.

I. Introduction

The undergraduate major of Electronic Engineering Technology at the University of Maryland Eastern Shore requires each student to complete a design course. The interface of a milling machine to a Motorola micro-controller was one of the design projects offered in this course1-3.

The milling machine was a small tabletop model that has a two-direction movable vise, and an adjustable height cutter head. A small 120-volt AC motor turns the cutter head. The cutter head speed can be controlled electronically from 200 to 2000 RPM’s. With the two-axis (X , Y) movable vise and the single axis (Z) movable cutter head, three axis (X, Y, Z) control of the cutting tool is achievable. Each axis is driven by a stepper motor turning a lead screw attached to the movable structure at one end. The other end is threaded through a fixed block and is coupled to the stepper motors.

The stepper motors utilized in the milling machine are bipolar and variable reluctance types with 200 discrete steps per revolution. The lead screws have 16 threads per inch of travel. It is possible to control the position of the cutter head to 1/3200 of an inch with a 1.8 degree step angle. The minimum power required by the stepper motors is 4.75V DC at 1 Ampere. This type of motor requires a push-pull bipolar drive circuit. The drive circuit

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Wagner, J., & Fotouhi, K., & Eydgahi, A. (2000, June), Microprocessor Controlled Milling Machine: A Student Project Paper presented at 2000 Annual Conference, St. Louis, Missouri. 10.18260/1-2--8564