초록 ▼

A shaft angle encoder comprises a code disc (21) mountable coaxially upon a rotary shaft (20) whose angular position is to be continuously measured. Coarse-bit angular position data are encoded digitally in Gray code by a pattern of opaque and transparent sectors provided on a plurality of inner ann

A shaft angle encoder comprises a code disc (21) mountable coaxially upon a rotary shaft (20) whose angular position is to be continuously measured. Coarse-bit angular position data are encoded digitally in Gray code by a pattern of opaque and transparent sectors provided on a plurality of inner annular tracks on the code disc (21). Fine-bit angular position data are encoded in analog triangular waveforms generated by the outermost annular track on the code disc (21). The analog position data are converted to fine-bit digital values, which are combined with coarse-bit digital values to obtain an angular position measurement. Alignment of the fine-bit digital values with the coarse-bit digital values obtained from the Gray code position data is accomplished by using information provided by overlapping the least significant bit of the coarse-bit digital values with the most significant bit of the fine-code digital values.

대표청구항 ▼

An apparatus for measuring rate of angular displacement of an object about an axis of rotation, said apparatus comprising: (a) a source of illumination; (b) means for detecting illumination emitted by said source, said detecting means including a plurality of photodetectors, each of said photodetect

An apparatus for measuring rate of angular displacement of an object about an axis of rotation, said apparatus comprising: (a) a source of illumination; (b) means for detecting illumination emitted by said source, said detecting means including a plurality of photodetectors, each of said photodetectors generating a corresponding electrical signal in response to illumination incident thereon; (c) a rotating plate for attachment to said object perpendicular to said axis of rotation, said rotating plate undergoing rotation corresponding to angular rotation of said object about said axis, said rotating plate having a plurality of annular tracks thereon, said tracks being at different radial distances from said axis, an outermost one of said tracks being aligned with a pair of said photodetectors, other ones of said tracks being aligned with corresponding other ones of said photodetectors, said rotating plate when attached to said object being disposed with respect to said source of illumination and said detecting means so that: (i) an opaque portion of each of said tracks prevents illumination emitted by said source from reaching said detector means, and (ii) a transparent portion of each of said tracks transmits illumination emitted by said source, the transparent portion of said outermost track comprising a plurality of elongate windows extending radially on said outermost track, said radially extending windows being equiangularly spaced around said outermost track; (d) a stationary plate interposed between said rotating plate and said detecting means when said rotating plate is attached to said object, said stationary plate having a pair of elongate windows, ends of each of said elongate windows on said stationary plate being generally aligned with corresponding annular boundaries of said outermost track on said rotating plate, said stationary plate also having a plurality of other windows, said other windows on said stationary plate being aligned with corresponding other ones of said annular tracks on said rotating plate, said stationary plate substantially preventing illumination that is transmitted by said radially extending windows on said outermost track on said rotating plate from reaching any photodetectors of said detecting means other than said pair of photodetectors aligned with said outermost track on said rotating plate, said stationary plate also substantially preventing illumination that is transmitted by the transparent portion of any one of said other tracks on said rotating plate from reaching any photodetectors of said detecting means other than the corresponding one of said other photodetectors with which said one of said other tracks is aligned; said pair of photodetectors that are aligned with said outermost track on said rotating plate comprising a first elongate photodetector and a second elongate photodetector disposed in quadrature, thereby establishing a condition in which: (i) when one elongate window on said outermost track on said rotating plate arrives at a position with respect to a first one of said pair of elongate windows on said stationary plate at which substantially all of the illumination that is transmitted by said one elongate window on said rotating plate is incident upon said first elongate photodetector aligned with said outermost track on said rotating plate, (ii) another elongate window on said outermost track on said rotating plate simultaneously arrives at a position with respect to a second one of said pair of elongate windows on said stationary plate at which only half of the illumination that is transmitted by said other elongate window on said rotating plate is incident upon said second elongate photodetector aligned with said outermost track on said rotary plate; so that said first and second elongate photodetectors generate corresponding first and second electrical signals as said object undergoes angular displacement, each of said first and second electrical signals being of generally triangular waveform, said first and second electrical signals being substantially equal to each other in amplitude and frequency but being out of phase with respect to each other; said other photodetectors of said detecting means that are aligned with corresponding other ones of said tracks on said rotating plate generating corresponding electrical signals as transparent portions of said other ones of said tracks arrive at positions with respect to corresponding ones of said other windows on said stationary plate at which illumination emitted by said source is incident upon said other photodetectors; and (e) electronic means including: (i) means for selecting which ever one of said first and second electrical signals generated by said first and second elongate photodetectors has an instantaneous value closer than the other of said first and second electrical signals to a mid-level amplitude value of said triangular waveform, and for inverting the selected one of said first and second electrical signals as necessary to provide correct polarity for producing an analog signal of generally triangular waveform that varies periodically as said object undergoes angular displacement, segments of said analog signal being substantially linear; (ii) means for converting said substantially linear segments of said analog signal to fine-bit digital signals; (iii) means for converting said electrical signals generated by said other photodetectors of said detecting means to coarse-bit digital signals; (iv) means for combining said fine-bit digital signals with said coarse-bit digital signals to obtain a digital measurement indicative of angular displacement of said object, said digital measurement having more bits obtained from said fine-bit digital signals than from said coarse-bit digital signals; and (v) means for differentiating said digital measurement with respect to time to obtain a digital measurement of the rate of angular displacement of said object.