Browse Prior Art Database

Forms Pedestal Switching Testing

IP.com Disclosure Number: IPCOM000053048D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Cavill, BR: AUTHOR [+2]

Abstract

There is described herein a circuit for diagnostically testing an open-loop forms feed motor system by checking the pedestal switching time. The forms drive in some printers may be an open-loop stepper motor driven system where the major components are the motor, driver board, and predriver card. The predriver card is essentially a memory device that translates input commands, such as stop or run, into motor commands and causes the correct switching of the appropriate stepper motor coils. In addition to this open-loop function, there exists a closed-loop function that operates the pedestal portion of the driver circuit. The pedestal feedback method allows coil current to be sensed and compared to a predetermined reference. When peak current is reached, the comparator fires, switching off the pedestal function.

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Forms Pedestal Switching Testing

There is described herein a circuit for diagnostically testing an open-loop forms feed motor system by checking the pedestal switching time. The forms drive in some printers may be an open-loop stepper motor driven system where the major components are the motor, driver board, and predriver card. The predriver card is essentially a memory device that translates input commands, such as stop or run, into motor commands and causes the correct switching of the appropriate stepper motor coils. In addition to this open-loop function, there exists a closed-loop function that operates the pedestal portion of the driver circuit. The pedestal feedback method allows coil current to be sensed and compared to a predetermined reference. When peak current is reached, the comparator fires, switching off the pedestal function.

A block diagram of the system is shown in Fig. 1. When the pedestal driver 10 is on, the motor 12 windings are driven with 48 volts, and when the pedestal driver 10 is off, then 10 volts drive the motor 12 windings. The pedestal driver 10 is active when enabled by the PEDESTAL ENABLE signal from microprocessor 14 and the current in the motor 12 windings is less than the reference voltage.

The forms system contains two identical window comparators 16 and 18. Their purpose is the control of the pedestal driver 10 by sensing motor 12 winding currents A and B. The pedestal driver 10 is switched on at the time of coil energization and is then switched off when a desired peak current is obtained. Sensing of motor 12 current is achieved by a low value series resistor, which develops a finite voltage when it experiences coil current; this voltage is felt at the input port of the window comparator 16 and 18.

A single chip microcomputer 14 provides the four time commutation signals through predriver 22 and driver 24, and controls the information to drive the stepper motor 12.

The motor will rotate when a specific step sequence is followed. The step sequence is illustrated in the table below. Note that two coils are always energized at any one time. See original.

The motor 12 operates at three speeds: "HI", "LOW", and "DETENT". "DETENT" motion uses only the 10 volt supply for drive. For "LOW" and "HI" speed motion, the pedestal driver 10 is activated and both 10 volts and 48 volts are used to drive the motor 12.

The pedestal driver 10 switches to an active pedestal voltage of 48 volts whenever more current is required. Microprocesso...