Electrical pulse counters – pulse dividers – or shift registers: c – Applications – Determining machine or apparatus operating time or...
Reexamination Certificate
1999-09-23
2001-03-06
Wambach, Margaret R. (Department: 2816)
Electrical pulse counters, pulse dividers, or shift registers: c
Applications
Determining machine or apparatus operating time or...
C377S017000
Reexamination Certificate
active
06198788
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to test apparatus for optical encoders and, more particularly, the instant invention relates to a test apparatus for an optical encoder used to determine the position of a door driven by a rotary drive member.
BACKGROUND OF THE INVENTION
It is well known in the transit vehicle art to open and close transit vehicle doors by rotating electric motors. In a typical transit vehicle door system a reversible electric motor turns a gear drive which in turn rotates a drive screw. A drive nut mounted on a door hanger is driven by the drive screw to open and close the door.
The rotation and the angular position of the shaft of the motor is, in some systems, sensed by an incremental optical encoder which has a rotor attached to the motor shaft and coaxial with the motor shaft. The rotor has indicia disposed in the angular direction around the rotor.
The indicia, for example, may be opaque angular segments separated by transparent angular segments. These segments may be formed on a flange which is coaxial with the motor shaft. An optical encoder may have a light emitting diode on one side of the rotor and a photoreceptor such as a photodiode on the other.
A single light emitting diode and photoreceptor provide a first pulsed binary signal as the motor rotates. A count of the pulses provides an indication of the angle through which the motor has rotated.
In order to determine the direction of rotation, a second photoreceptor is also generally employed. It observes the first light emitting diode or a second light emitting diode. It is positioned so that it provides a second pulsed binary signal which is in quadrature relationship to the first pulsed binary signal.
In a typical optical encoder, for example, there are 500 transparent segments each having an angular extent of 0.36 degrees. Likewise there are 500 opaque segments, each having an angular extent of 0.36 degrees. The opaque segments alternate with the transparent segments. Each transparent segment and its following opaque segment together occupy an angle of 0.72 degrees.
To obtain the quadrature signal, the second photoreceptor is located at an angular position of (N*0.72)+0.18 degrees relative to the first photoreceptor, N being any integer.
When the motor rotates in one direction, pulses obtained from the first photoreceptor precede the pulses from the second photoreceptor. When the motor rotates in the opposite direction, pulses from the second photoreceptor precede the pulses from the first photoreceptor. A signal processor or logical device which controls the motor is programmed to utilize the pulses from the first and second photoreceptors to determine the direction of rotation of the motor, as well as its angular velocity and, by summation, calculate the angle through which it has rotated. In this manner, the signal processor or logical device continually has information defining the position and velocity of the door.
Some commercially available encoders also have a third photoreceptor which observes a light emitting diode. These pass light through a portion of the rotor having, for example, one small transparent angular segment and one opaque angular segment covering the rest of the 360 degrees. These provide one index pulse per revolution of the rotor. This single index pulse is used to verify the position obtained from the quadrature signals.
Optical encoders are subject to deterioration with time, making their output susceptible to electrical noise, which may make the edges of the pulses uncertain. There may also be crosstalk between the signals obtained from the photoreceptors. In addition, there may also be spurious signals on the lines from the photoreceptors due to electromagnetic interference.
SUMMARY OF THE INVENTION
The present invention is an apparatus for testing an optical encoder used to determine a position of a moveable member. The moveable member may, for example only, be a rotary drive member in a transit vehicle door system. The optical encoder supplies a first binary signal indicative of an angular position of the moveable member and a second binary signal indicative of the angular position, the first binary signal and the second binary signal being in quadrature relationship. The apparatus includes a first delay device connected to receive the first binary signal and for producing a first delayed binary signal. The apparatus further includes a first logic gate connected to receive the first binary signal and the first delayed binary signal. The first logic gate produces a first edge detection pulse signal. The apparatus further includes a second delay device connected to receive the second binary signal and for producing a second delayed binary signal. The apparatus also includes a second logic gate connected to receive the second binary signal and the second delayed binary signal. Such second logic gate produces a second edge detection pulse signal. The first edge detection pulse signal and the second edge detection pulse signal are used to qualify the optical encoder.
In another aspect, the invention is a method of testing an optical encoder used to determine a position of a moveable member. The optical encoder supplies a first binary signal indicative of a position of the moveable member and a second binary signal indicative of the position, the first binary signal and the second binary signal being in quadrature relationship. The method includes producing a first delayed binary signal and combining the first binary signal with the first delayed binary signal to produce a first edge detection pulse signal. The method also includes producing a second delayed binary signal and combining the second binary signal with the second delayed binary signal to produce a second edge detection pulse signal. The first edge detection pulse signal and the second edge detection pulse signal are for qualifying the optical encoder.
OBJECTS OF THE INVENTION
It is, therefore, one of the primary objects of the present invention to provide an apparatus for detecting deterioration of an optical encoder used to determine the position and velocity of a moveable member.
An additional object of the present invention is to provide an apparatus for detecting deterioration of an optical encoder used to determine the angular position and velocity of a rotary drive member.
Another object of the present invention is to provide an apparatus for detecting deterioration of an optical encoder used to determine the position and velocity of a load which is moved by a rotary drive member.
Still another object of the present invention is to provide an apparatus for detecting noise in the signal from a photoreceptor in an optical encoder used to determine the angular position and velocity of a rotary drive member.
Yet another object of the present invention is to provide an apparatus for detecting noise in the signal from a photoreceptor in an optical encoder used to determine the position and velocity of a load which is driven by a rotary drive member.
A further object of the present invention is to provide an apparatus for detecting an overspeed condition of an electric motor having an optical encoder.
It is an additional object of the present invention to provide an apparatus for detecting an overspeed condition of a powered door which is driven by a rotary drive member.
Still yet another object of the present invention is to provide an apparatus for detecting failure of an incremental optical encoder.
Yet still another object of the present invention is to provide a method for detecting deterioration of an optical encoder used to determine the angular position and velocity of a rotary drive member.
Another object of the present invention is to provide a method for detecting deterioration of an optical encoder used to determine the position and velocity of a load which is moved by a rotary drive member.
In addition to the various objects and advantages of the present invention which have been generally described above, there will be various other objects and advantages
James Ray & Associates
Wambach Margaret R.
Westinghouse Air Brake Company
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