Browse Prior Art Database

Motor Timing Control Circuit

IP.com Disclosure Number: IPCOM000047341D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Hutson, DJ: AUTHOR [+2]

Abstract

This timing control circuit senses motor speed and corrects for changes in motor speed caused by transient shifts in the power line frequency servicing the motor. In one application example, the basic timing of a pulsed laser drill (not shown) is derived from a chopper disk (not shown) which is driven by a hysteresis synchronous motor (not shown). As a result, any transient shift in the line frequency causes a corresponding shift in the motor speed and consequently the timing signals. This circuit compensates for the shift in timing. The basic operation of the laser drill acoustic sensing is shown in the timing diagram of Fig. 1. The laser pulse control signal B produced by the chopper disk starts drilling a hole at the proper location on a workpiece, such as a printed circuit (PC) panel or the like (not shown).

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Motor Timing Control Circuit

This timing control circuit senses motor speed and corrects for changes in motor speed caused by transient shifts in the power line frequency servicing the motor. In one application example, the basic timing of a pulsed laser drill (not shown) is derived from a chopper disk (not shown) which is driven by a hysteresis synchronous motor (not shown). As a result, any transient shift in the line frequency causes a corresponding shift in the motor speed and consequently the timing signals. This circuit compensates for the shift in timing.

The basic operation of the laser drill acoustic sensing is shown in the timing diagram of Fig. 1. The laser pulse control signal B produced by the chopper disk starts drilling a hole at the proper location on a workpiece, such as a printed circuit (PC) panel or the like (not shown). The number of laser pulses needed to completely drill a hole is determined by processing the output signal C of an acoustic sensor (not shown) located in close proximity to the hole being drilled. The acoustic sensor responds both to light and sound.

Thus, its output signal C will contain optical information at the beginning and acoustic information somewhat later in time. The value obtained by integrating the acoustic portion of the total signal is the desired information needed to determine drill completeness. The integration start time has to be positioned after the optical information has subsided. The timing is developed from the disk synchronizing pulses of signal A. Each laser pulse of signal B occurs between two consecutive pulses of signal A at a predetermined time interval D before the second pulse of the particular consecutive pulse pair of the signal A. The predetermined nominal speed of the synchronous motor determines the base cycle time E, and hence variations in line frequency cause the motor speed to change which causes changes in cycle time. The start T1 of the integration point, which is keyed from signal A, must shift proportionally to motor speed changes or error will be introduced into the integration result due to the presence of optical information or too little acoustic information. The circuit shown in Fig. 2 measures cycle time and proportionally corrects the start of integration time point in the next cycle based on the time measurement acquired from the previous cycle. Measurements of motor transient response indicate that the speed change due to a step change in line frequency is very long compared to the nominal...