Boots – shoes – and leggings
Patent
1988-02-09
1990-08-14
Teska, Kevin J.
Boots, shoes, and leggings
36447428, 364560, 36457101, 377 17, 73 1R, G06F 1546, G06F 15353
Patent
active
049492896
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to apparatus for determining values of a periodic function by interpolation.
Known such apparatus comprises reading means for reading at least four values of the periodic function and converting means for converting said at least four values into a pair of derived sine and cosine functions. Interpolation values are determined by establishing the relationship between values of the sine and cosine functions at given intervals.
The reading means is only capable of reading values of the periodic function comforming to a given nominal phase separation, since it will have transducers at a given spacing from each other. Also, the interpolation is only accurate to the extent that the phase difference between the sine and cosine functions is 90.degree.. Disconformity between any actual phase separation and said given phase separation results in departure of said sine and cosine functions from said 90.degree. phase difference and in consequent inaccuracy of the interpolation. For example, such disconformity may arise if the periodicity of the periodic function does not accurately agree with the spacings of the transducers.
In known said apparatus the converting means is adapted for producing said sine and cosine functions each as a function of two said values of the periodic function. For example, if the four values are represented by signals A, B, C and D nominally in quadrature, the sine and cosine functions may be respectively derived by combining these signals as (A-C) and (B-D). This results in substantial dependence of said accuracy on said phase separation.
SUMMARY OF THE INVENTION
In the present invention, the converting means includes means for producing at least one derived signal by combining at least three scanning values or signals. At least in a preferred embodiment, this reduces the dependence of the accuracy of the interpolation on the phase separation.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of apparatus according to this invention will now be described with reference to the accompanying drawings wherein:
FIG. 1 is an elevation of the mechanical arrangement of a scale-reading apparatus.
FIG. 2 is a plan view of FIG. 1.
FIG. 3 is a diagram of a periodic light signal and an associated arrangement of light-sensing diodes.
FIG. 4 shows an electrical circuit network in which the outputs of said diodes are combined.
FIG. 5 is a diagram of sine and cosine functions being outputs of said circuit network.
FIG. 6 is a diagram showing the effect of changes in the phase separation of said light signal.
FIG. 7 is a vector diagram illustrating the operation of the circuit network of FIG. 4.
FIG. 8 is a diagram corresponding to FIGS. 3 and 4 but illustrating a modified embodiment.
FIG. 9 is a vector diagram illustrating the operation of the embodiment of FIG. 8.
FIG. 10 is another diagram corresponding to FIGS. 3 and 4, illustrating a further modified embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A scale 10 (FIGS. 1,2) having length in a direction X has linear marks 11 extending in a direction Y perpendicular to the direction X. The marks have a spacing P10. A readhead 13 is supported for linear displacement in the direction X. The readhead 13 has an index grating 12 set at an angle .alpha. to the scale marks 11 to produce a periodic function having the form of a moire fringe signal 142 (FIG. 3). The signal 142 is defined by a substantially sinusoidally varying light intensity plotted against displacement values Y1 of the moire fringes over the grating 12.
The signal 142 has a period P22, and a corresponding phase separation or quadrature Q22. The period P22 and quadrature Q22 are a function of the angle .alpha.. The readhead 13 includes a reading means in the form of four transducers or photodiodes 16 or 16A, 16B, 16C, 16D positioned at equal spacings P30 relative to the grating 12 so as to produce four quadrature voltage or scanning signals A, B, C, D corresponding to quadrature light intensity values QA, QB, QC, QD of the signal 142. As d
REFERENCES:
patent: 3868680 (1975-02-01), Rhodes
patent: 3976869 (1976-08-01), Stella et al.
patent: 4346447 (1982-08-01), Takahama
patent: 4443788 (1984-04-01), Breslow
patent: 4462083 (1984-07-01), Schwefel
patent: 4468745 (1984-08-01), Kjosavik
patent: 4587622 (1986-05-01), Herzog
patent: 4595991 (1986-06-01), Spies
patent: 4618940 (1986-10-01), Schmitt
Pleydell Mark E.
Stephens W. F. Noel
Renishaw plc
Teska Kevin J.
LandOfFree
Interpolation apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Interpolation apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Interpolation apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-467787