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Browse Prior Art Database

THREE PHASE MOTOR DRIVER

IP.com Disclosure Number: IPCOM000025631D
Original Publication Date: 1986-Dec-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 206K

Publishing Venue

Xerox Disclosure Journal

Abstract

In laser scanner systems, a major contributor to print quality (line to line pixel placement) is the polygon motor and its associated driver. In a typical scanner, a hysteresis synchronous motor is used with either two or three phase windings. The two phase designs require positive and negative power supplies and quadrature (90" phase shift) waveforms. Three phase motors on the other hand are driven with the 120" phased waveforms and require only one power supply.

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XEROX DISCLOSURE JOURNAL

THREE PHASE MOTOR DRIVER

Proposed Dale C. Thomas U.S. C1.3181498 Classification

Int. C1. H02p 1/00

-0

-L. 7-7 I

PE

I-

In laser scanner systems, a major contributor to print quality (line to line pixel placement) is the polygon motor and its associated driver. In a typical scanner, a hysteresis synchronous motor is used with either two or three phase windings. The two phase designs require positive and negative power supplies and quadrature (90" phase shift) waveforms. Three phase motors on the other hand are driven with the 120" phased waveforms and require only one power supply.

In addition to the two motor types referred to above, there are also two types of driving waveforms used. Some printer motors are squarewave driven while others are sinusoidally driven.

When comparing this 2x2 matrix of motor and waveform types, some advantages of the three phase squarewave system became readily apparent. First of all, the squarewave design with its switching drive transistors inherently operates much cooler than the sinusoidal design where the

Volume 11 Number 6 November/December 1986 259

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THREE PHASE MOTOR DRIVER (Cont'd)

transistors are operated in a linear mode. Hence, there is much less wasted power and heat buildup, especially when Pow power factor motors are used. Secondly, the single power supply of the three phase design is a distinct advantage over two phase dual supplies, especially when closed loop power supply control is used to minimize motor hunting.

From these operational considerations, it would seem that the three phase squarewave approach would be the design of choice. However, every motor phase requires a separate driver and, thus, three phase designs have historically been more expensive then their two phase counterparts. For example, three phase design requires a total of 18 transistors while two phase designs only require 8. These extra 10 transistors and the incremental Printed Wiring Board (PWB) space to mount them produces a significant cost disadvantage for the three phase design.

The purpose of this suggestion is to eliminate this cost disparity between the two types of drivers making the three phase system with its inherent advantages a viable economic alternative. In this context, a three phase motor driver must perform the following three essential functions:

1) Three phase timing generation

2) Power-up and loss of clock resets to prevent continuous current

3) Power switching of the windings

to a single winding, and

This proposal achieves these three functions utilizing relatively few components that are all low cost and readily available. Referring to the drawing Figure, three phase timing is generated from a single CMOS IC which performs as a presetable divide by N counter 4 operating as a divide by
6. Operating counter 4 in this mode produces the three 120" phase shifted waveforms simultaneously at a frequency 1/6...