Coded data generation or conversion – Digital pattern reading type converter – With directional discrimination
Reexamination Certificate
2000-08-08
2001-10-09
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Digital pattern reading type converter
With directional discrimination
C341S008000, C341S011000, C341S116000, C318S560000, C318S561000, C318S062000, C324S160000
Reexamination Certificate
active
06300884
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to quadrature encoding and specifically to a method of decoding quadrature encoded signals.
RELATED ART
Motor controllers determine the angular or linear position of the motor and the number of revolutions of the motor to make a decision regarding control of the motor. The controller may provide feedback to implement the decision or may store the information for accounting purposes, such as to determine usage and wear of the motor. Typically an encoder is attached to the shaft of the motor. The encoder includes a disk having slots located around the perimeter. As the shaft rotates, the disk passes through a reader which detects the slots as they rotate. The revolution of the motor is determined by counting the number of slots passing through the reader. The reader is typically a slot type sensor that includes a light emitting diode (LED) on one side and a photoreceiver on the other.
Incremental quadrature encoders embed the position information into Two (2) signals with a quadrature phase relationship. Quadrature encoding is implemented by positioning Two (2) receivers each generating a signal. The encoded signals are then referred to as Channel A and Channel B. Direction information is encoded as the differential of the phase polarity of the signals, Channel A and Channel B. In one example, when the shaft rotates in a first direction, referred to as forward, Channel A is 90° out of phase with Channel B with Channel A leading Channel B. When the shaft rotates in the reverse direction, referred to as backward, Channel B leads Channel A. As the quadrature encoder generates Two (2) digital signals, and therefore there are Four (4) possible encoder states, HH, HL, LL, LH, where H refers to a logical high level and L refers to a logical low level.
Extraction of the position and direction information from these signals is often costly. Specifically, when the shaft rotates forward a counter increments on each state transition to identify position. When the shaft rotates backward the counter decrements on each state transition. Monitoring thus requires tracking each transition of the encoded signals.
According to one method, the motor controller monitors the signals in software to calculate position and direction. The resolution of the encoder is determined by the number of slots in the encoder disk. For high resolution encoders operating at high speed, many encoder edges are generated per second. The encoder interrupts the controller, or specifically a processor in the controller, on each transition of the signals. This requires excessive controller bandwidth as the controller performs the calculations using the encoder edges of both signals. The monitoring of the motor is thus limited by the speed of the encoder and the speed of the controller.
One method of control reduces the required bandwidth by monitoring only a single edge of one signal, such as the falling edge of Channel B. If the motor slows down, all edges are again monitored. This method reduces interrupts to the controller by a factor of Four (4) requiring only one quarter of the bandwidth. While an improvement, this method is still limited by the speed of the encoder and the controller. Additionally, the resolution of the encoder is reduced by a factor of Four (4).
Another type of controller provides the monitoring and calculations in external decode hardware. A problem exists as the decode hardware increases the size of the controller incurring greater expense.
A need therefore exists for a method of decoding a quadrature encoded signal in which the calculations are independent of the encoder edges. Additionally, it is desirable to reduce the number of interrupts to a controller used for decoding the quadrature encoded signals and thus reduce the impact on the bandwidth of the controller.
REFERENCES:
patent: 5130710 (1992-07-01), Salazar
patent: 5187479 (1993-02-01), Johnson, III et al.
patent: 5377232 (1994-12-01), Davidov et al.
patent: 6097319 (2000-08-01), Liu
Optoelectronics Designer's Catalog, Hewlett-Packard Co., pp. 86-101 (1993).
Chiu Joanna G.
Mai Lam T.
Motorola Inc.
Tokar Michael
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