Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Cathode ray
Patent
1990-04-26
1992-07-07
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Cathode ray
324 83Q, 324 88, 340743, G01R 1320, G01R 1328
Patent
active
051286092
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to methods and apparatus to assist in the setting up of devices which produce output signals in quadrature, for example so as to ensure that the output signals are accurately in a 90.degree. phase relationship, or accurately of the same amplitude, or accurately with zero DC offsets.
Such a method and apparatus are useful in setting up a scale and readhead, such as used on co-ordinate measuring machines or machine tools, to determine the position of a movable part of such a machine relative to a fixed part. It is well known to provide such scales and readheads wherein the readhead has two outputs in quadrature. These outputs can be fed to further circuitry for counting the cycles of the incoming signals so as to determine position, for determining the direction of movement by determining which of the quadrature signals leads the other, and/or for providing position interpolation within one cycle of the output. Of course, it is desirable that the readhead should be set up correctly aligned relative to the scale such that the outputs are accurately in quadrature, with a 90.degree. phase shift, the same amplitudes and with zero DC offsets. Particularly in the case where the signals are to be fed to an interpolator, this can affect the accuracy of the resulting determination of the relative position.
An example of a scale and readhead providing quadrature outputs to an interpolator is shown in European Patent Application No. EP-0274841-A.
One way to determine such factors would be to feed the two quadrature signals to the X and Y inputs of an oscilloscope. This produces a Lissajous figure, which should be a perfect circle centred on zero if all of the above factors are correctly set up. The mechanical position of the readhead relative to the scale can be adjusted to achieve this. However, it is very difficult to judge whether the Lissajous figure observed is perfect. The results also depend upon the accuracy of calibration of the oscilloscope, for example ensuring that the gains of its X and Y channels are exactly matched and that neither introduces a DC offset.
SUMMARY OF THE INVENTION
One aspect of the present invention provides a method of setting up a device which provides two signals in quadrature, comprising:
processing said quadrature signals in a processing circuit which has at least one output line, said processing circuit including means for combining the quadrature signals, to give at least one combined output signal on said at least one output line, representative of the alignment of the quadrature signals;
passing said at least one combined output signal to a display device and displaying an indication of said alignment of the quadrature signals; and
adjusting said device which provides the quadrature signals to improve the indicated alignment.
A second aspect of the present invention provides a method of setting up a device which provides two signals in quadrature, comprising producing on an oscilloscope screen two superimposed Lissajous figures derived from the quadrature signals, one of the Lissajous figures being a rotation or reflection of the other, and adjusting the device so as to improve the co-incidence of the Lissajous figures.
Further aspects of the invention provide apparatus for use in performing the above methods.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, wherein:
FIG. 1 is a block schematic diagram of a first embodiment, connected to a scale and readhead,
FIGS. 2 and 3 are circuit diagrams of two further embodiments, and
FIG. 4 is a waveform diagram for the circuit of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is a scale 10 along which a readhead 12 can be traversed, producing SIN and COS outputs 14, 16 which are (at least nominally) in quadrature. When installing the scale 10 and readhead 12 on a machine such as a co-ordinate measuring machine or machine tool, it is required
REFERENCES:
patent: 3305843 (1967-02-01), Scuitto
patent: 3476974 (1969-11-01), Turnage, Jr. et al.
patent: 3484684 (1969-12-01), Lipscombe
patent: 3582773 (1971-06-01), Karl
patent: 3746912 (1973-07-01), Redecker et al.
patent: 3789200 (1974-01-01), Childress et al.
patent: 4041254 (1977-08-01), Bradley et al.
patent: 4149155 (1979-04-01), Kishi
patent: 4405895 (1983-09-01), Girst et al.
patent: 4459543 (1984-07-01), McNeill
patent: 4631533 (1986-12-01), Mark, Jr.
patent: 4648113 (1987-03-01), Horn
patent: 4680620 (1987-07-01), Baker et al.
Kuz'minskii et al "Device for Adjustment of precision Motion Transducers", Instruments & Experimental Techniques, vol. 30, No. 6 Part 2, Nov./Dec. 1987 pp. 1497-1499.
Bergmann, "Elektrische Messtechnik" 1981, pp. 133-134 The Radio Amateur's Handbook, 1981, 58th Ed. pp. 4-61.
"A Versatile Phase Meter" by Patchett et al. Electronic Engineering, May 1952, pp. 224-229.
Burns William J.
Renishaw plc
Wieder Kenneth A.
LandOfFree
Setting up of quadrature signals does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Setting up of quadrature signals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Setting up of quadrature signals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1832030