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Minimizing the Effects of Eccentricity on Rotary Emitter Disks

IP.com Disclosure Number: IPCOM000039863D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 4 page(s) / 43K

Publishing Venue

IBM

Related People

Crowell, JW: AUTHOR

Abstract

Stepper motors commonly use a shaft-mounted, rotary emitter disk to run the motor in the open- or closed-loop mode. It is important to minimize the eccentricity of the system when running the motor in the closed-loop mode. The eccentricity of the system is the sum of the eccentricity of the motor, shaft, disk and disk mountings. In the closed-loop mode, the stepper motor is given a series of pulses to move it one step, when a feedback (FB) pulse is sensed from the disk. The rotary emitter disk works in conjunction with a magnetoresistive sensor (MR Sensor) or light sensor to create FB pulses. The MR Sensor detects (Image Omitted) changes in magnetic flux when the rotary emitter rotates from window to land or land to window. The MR Sensor must be aligned with respect to a window or land on the rotary emitter.

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Minimizing the Effects of Eccentricity on Rotary Emitter Disks

Stepper motors commonly use a shaft-mounted, rotary emitter disk to run the motor in the open- or closed-loop mode. It is important to minimize the eccentricity of the system when running the motor in the closed-loop mode. The eccentricity of the system is the sum of the eccentricity of the motor, shaft, disk and disk mountings.

In the closed-loop mode, the stepper motor is given a series of pulses to move it one step, when a feedback (FB) pulse is sensed from the disk. The rotary emitter disk works in conjunction with a magnetoresistive sensor (MR Sensor) or light sensor to create FB pulses. The MR Sensor detects

(Image Omitted)

changes in magnetic flux when the rotary emitter rotates from window to land or land to window. The MR Sensor must be aligned with respect to a window or land on the rotary emitter. If the disk is not in correct alignment with the sensor, the FB pulses will occur at the wrong time and the motor will not run correctly. The degradation of motor performance will necessitate an adjustment of the sensor to align the sensor with a window or land on the disk. A method of making this adjustment is described in this article. The eccentricity of the system must be considered before making the sensor adjustment. In this method of sensor adjustment the eccentricity of the system is divided in half and distributed equally along the two halves of the disk. The optimum point for adjustment (OPA) must be found before any adjustment can be made. For descriptive purposes, only windows will be discussed. In reality, however, the change from land to window will cause a FB, as will a change from window to land.

(Image Omitted)

There is no eccentricity in Fig. 1, that is, the center is the same as the theoretical center and the x and y axes of the disk are the same as the theoretical x and y axes. These terms will now be defined. 1. The center is the actual center of the disk, which

is affected by the eccentricity of the system.

2. The theoretical center is where the center of the

disk would

be if the system was concentric. 3. The axes are the actual axes of the disk, which are affected

by the eccentricity of the system.

4. The theoretical axes are where the axes of the

disk would be if the system was concentric.

(Image Omitted)

The OPA is found in

1

Page 2 of 4

the following manner:

1. Measure 360 FB times (1 motor revolution) in the

open-loop mode. One FB time equals the time

between the initial motor advance and the arrival

of the FB pulse. These FB times will vary in

relation to the position of the revolution due to

the eccentricity.

A. Refer to Fig. 2. When window A passes

through the magnetic field, the eccentricity

of the system causes the window to be higher

than normal. However, the window is in the

center of the magnetic field with respect to

the x axis. Therefore, when the motor is

rotated clockwise, the resulting FB time will

be correct (FB time A).

(Im...