Electricity: measuring and testing – Magnetic – Displacement
Patent
1997-10-20
2000-04-18
Patidar, Jay M.
Electricity: measuring and testing
Magnetic
Displacement
3242072, 324202, 32420712, 33708, G01R 3500, G01R 33025, G01B 714, G01D 5245
Patent
active
060519711
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a scale reading apparatus of the type including a scale defined by a series of spaced apart lines, and a readhead movable relative to the scale in the direction of spacing of the lines. In one type of such apparatus, the readhead includes a light source which illuminates the scale, and a number of optical components which co-operate with the scale to generate a periodic light pattern. Relative movement of the scale and readhead results in a corresponding movement of the periodic light pattern, creating a cyclic light intensity modulation. The readhead also includes a plurality of photodetecting elements upon which the light intensity modulation is incident, and which emit a plurality of phase-shifted cyclically modulating electrical signals corresponding to the light intensity modulation. These signals are sent to a signal conditioning circuit which combines the signals, and generates therefrom a pair of sinusoidally varying signals having a quadrature relationship; the magnitude and direction of relative movement of the readhead and scale are determined from these quadrature signals.
Devices of this type usually function in an incremental fashion. The quadrature signals output from the signal conditioning circuit serve as a basis for generating a total on a counter, indicative of the relative displacement of the scale and readhead. The total on the counter is either augmented or reduced in correspondence with the number of quadrature signal cycles received, and the order in which these signals arrive at the counter. However, it is also necessary to provide an absolute indication of the relative position of the scale and readhead, for example in order that any error maps associated with the scale may be initialised from the same repeatable location. This is typically provided by a reference mark provided on the scale which causes the readhead to emit a zero pulse when a reference detector in the readhead comes into register with the reference mark. To provide the best stability for the apparatus against thermal drift, for example, the zero pulse from the readhead is preferably emitted at a mid point in the cycle of the quadrature signals. To ensure that this is the case, the relative phase of the quadrature cycle and the zero pulse must be adjustable.
According to the present invention, there is provided an opto-electronic scale reading apparatus including a scale, defined by a series of spaced apart parallel lines, and a readhead movable one relative to another in the direction of spacing of the lines, the readhead including: a light source which illuminates the scale; one or more optical components which co-operate with the scale to generate a periodic light pattern and a cyclically modulating light intensity upon said relative movement; one or more photodetectors and associated electronic processing circuitry for generating a pair of sinusoidally modulating signals having a quadrature relationship from which the magnitude and direction of relative movement may be determined, said apparatus further comprising a reference mark provided on the scale in the form of a ferromagnetic element, and a magnetic sensor in the readhead, wherein said magnetic sensor generates a reference pulse when a predetermined relationship is attained with the ferromagnetic element, and wherein magnetic flux intensity in the region of the magnetic sensor when the readhead lies adjacent the reference mark may be varied by adjustment of the position of a further ferromagnetic element either connected to and movable relative to the first mentioned ferromagnetic element or in the vicinity of said sensor in said readhead, wherein said further ferromagnetic element has a permeability substantially greater than that of free space.
Preferably a magnetic field is generated by a permanent magnet which is provided either in the readhead, or by the ferromagnetic element. A magnetic field source independent of the reference mark and the readhead may however be employed.
An embodiment of the present invention w
REFERENCES:
patent: 4074258 (1978-02-01), Dore et al.
patent: 4143267 (1979-03-01), Johnson et al.
patent: 4400890 (1983-08-01), Ohkubo et al.
patent: 4421980 (1983-12-01), Kuhne
patent: 4492861 (1985-01-01), Kebschull et al.
patent: 4616131 (1986-10-01), Burkhardt
patent: 4829248 (1989-05-01), Loubier
patent: 5500589 (1996-03-01), Sumcad
Patidar Jay M.
Renishaw plc
LandOfFree
Scale reading apparatus with a magnetic sensor unit for adjustin does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Scale reading apparatus with a magnetic sensor unit for adjustin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Scale reading apparatus with a magnetic sensor unit for adjustin will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2338751