Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1998-06-03
2001-02-06
Ham, Seungsook (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S231130
Reexamination Certificate
active
06184518
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to rotary encoders for detecting an angle of rotation, and more particularly to a rotary encoder including multiple calibration points allowing the rotary encoder to be calibrated by turning it through only a fraction of a complete 360-degree rotation.
2. Related Art
Rotary encoders are the sensor of choice for generating a digital output to accurately measure rotational motion. Encoders are often attached to high performance spindles in systems such as high precision machine tools and laser scanners. They are used to measure rotational parameters such as shaft angle position, velocity and direction of rotation.
A rotary encoder typically has two or three signal channels. One of these channels is generally a one-pulse-per-revolution index channel, and the other channels are generally multiple-pulse-per-revolution data channels. The number of pulses per revolution on a data channel is typically between a few hundred and a few thousand depending upon the resolution required for fine position control. These signals are often fed into a control system to provide real-time information regarding the position, velocity and rotational direction of the spindle.
The index channel pulse is used to indicate the beginning of each spindle revolution, and the data channel(s) signal is used to indicate the speed of the rotor and the angular position of the rotor within a revolution. For some types of encoders (such as a quadrature type encoder) there is an additional channel which provides information on the direction of the spindle.
FIGS. 1A and 1B
illustrate portions of a prior art rotary encoder. The rotary encoder illustrated in
FIGS. 1A and 1B
includes rotatable disk
100
, which is coupled to shaft
101
. Shaft
101
is coupled to a rotational input, such as a spindle for a machine tool, so that rotating the spindle cases shaft
101
and disk
100
to rotate. Disk
100
includes two channels comprising circumferentially extending rows of transparent openings through which light can pass. In the illustrated example, the inner channel is an index channel
102
, with a single opening (pulse) per revolution specifying an index position. The outer channel is a data channel
104
with a large number of openings (pulses) specifying incremental angular displacements of disk
100
. Rotatable disk
100
is typically composed of glass, and the openings which form index channel
102
and data channel
104
are typically etched in rotatable disk
100
.
In the illustrated example, information from index channel
102
and data channel
104
is retrieved optically. Light emitting device
106
generates light, which passes through index channel
102
and feeds into light receiving device
112
. The signal from light receiving device
112
passes into signal processing device
114
, which detects and decodes the index pulse from index channel
102
. Similarly, light emitting device
108
generates light, which passes through data channel
104
and feeds into light receiving device
110
. The signal from light receiving device
110
passes into signal processing device
114
, which detects and decodes an angular displacement signal from data channel
104
. Light emitting devices
106
and
108
are typically implemented using light emitting diodes (LEDs) or lasers. Light receiving devices
110
and
112
are typically implemented using photodiodes. Signal processing device
114
is typically implemented with a device controller or a microprocessor.
One problem with the above-described rotary encoder design is that it requires up to a complete revolution of the rotary encoder to detect the pulse on the index channel in order to calibrate the rotary encoder. Turning the rotary encoder through a complete revolution may not be possible or may be inconvenient for certain applications, such as a wind direction indicator, a rudder position indicator or a joystick.
What is needed is a rotary encoder that can be calibrated without having to turn it through a complete revolution.
A rotary encoder with multiple index points has previously been disclosed. See U.S. Pat. No. 5,130,536, entitled “Optical Rotary Encoder with Indexing,” to Sato et al. However, the rotary encoder disclosed in Sato was developed to facilitate the firing of spark plugs, not for purposes of calibration. Hence, the multiple index points in Sato do not contain information specifying angular positions for the index points for purposes of calibration. In
FIG. 2
of the Sato patent, the zero angle index point contains a marker with two openings to differentiate it from the other index points. The other index points merely include a marker with a single opening, and these other index points cannot be differentiated from one another for purposes of calibration. (See
FIG. 2
) Hence, it is necessary to turn the rotary encoder disclosed in Sato through almost a complete revolution in order to calibrate it. (Strictly speaking, it is possible to calibrate this encoder by turning it though 1-1/N revolutions, where N is the number of index points.)
SUMMARY
One embodiment of the present invention provides a rotary encoder having a rotatable disk with multiple index points. These index points contain information specifying an angular position of the index point. This allows the rotary encoder to be calibrated by turning it through a sufficient angular displacement to ensure that an index point passes over an optical sensor. This sufficient angular displacement is less than a complete revolution because there are multiple index points along the circumference of the disk. This design allows a rotary encoder to be calibrated without turning it through a complete revolution. This is advantageous where turning the rotary encoder through a complete rotation is not possible or is inconvenient, for example in applications such as a wind direction indicator, a rudder position indicator or a joystick. Thus, the one embodiment of the present invention can be characterized as an optical rotary encoder including a rotatable disk. The rotatable disk includes an index channel with a single circumferentially extending row of at least two index points located on equally-spaced radii, each index point encoding information specifying an angular position of the index point along the circumference of the disk. The rotary encoder also includes a first light emitting device disposed to illuminate the index channel, and a first light receiving device disposed to receive light from the illuminated index channel. The rotary encoder additionally includes a signal processing device coupled to the first light receiving device for converting signals from the first light receiving device into an index signal.
Another embodiment of the present invention includes a data channel disposed on the rotatable disk, for measuring an angular displacement. This data channel includes a single circumferentially extending row of data pulses located on equally-spaced radii, wherein each data pulse specifies an incremental angular displacement of the disk. This embodiment also includes a second light emitting device disposed to illuminate the data channel, and a second light receiving device disposed to receive the illuminated data channel. Additionally, the signal processing device is coupled to the second light receiving device and it converts signals from the second light receiving device into an angular displacement signal.
In another embodiment of the present invention, the data channel occupies the same circumferentially extending row on the disk as the index channel. In this embodiment, the first light emitting device and the second light emitting device are the same device, and the first light receiving device and the second light receiving device are the same device (see FIG.
5
A and FIG.
5
B). In another embodiment, the data channel and the index channel occupy different circumferentially extending rows on the disk.
Another embodiment of the present invention includes a calibration mechanism coupled to the signal process
Ham Seungsook
Micron Electronics Inc.
Park & Vaughan LLP
Pyo Kevin
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