Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1985-07-25
1988-01-05
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
340347P, 324175, 356395, H01J 314
Patent
active
047178248
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a photoelectric displacement detecting apparatus, and more particularly to improvements in a photoelectric displacement detecting apparatus comprising a main scale with a length-measuring slit row having regular pitches, an index scale provided thereon with a length-measuring gate slit row being equal in pitch to the length-measuring slit row of the main scale and disposed in a manner to be in parallel to the direction of the slit row and movable relative to the main scale, and a length-measuring photo-electric transducer for receiving light transmitted through or reflected by the main scale and the index scale producing a length-measuring signal from the number of repeated bright and dark portions of the light formed by the repetitions of overlappings of respective slits during a relative movement between the main scale and the index scale.
2. Background Art
The photoelectric displacement detecting apparatus of the type described are adopted in many fields because displacements can be detected in non-contact with an object to be detected and with high accuracy. However, since with such a functional curve that the detection signals repeat the increases or decreases against the length-measuring direction is drawn, even if a detection signal is processed to be turned into a digital signal, for example, and indicated digitally, the physical absolute origin is unclear only from this signal. In consequence, there has been needed another means to specify the absolute origin.
As measures for specifying the absolute origin in the photoelectric displacement detecting apparatus of the type described, there have heretofore been types shown below.
Firstly, there is a method for forcibly zero-setting an indicated value of digital indicators, including a counter and the like, when the main scale and the index scale are in a desirable positional relationship to each other.
This method is easy and simple, however there are some cases where it is difficult to determine the absolute origin with the accuracy of .mu.m order.
Furthermore, when the power is cut off during measurement, a repeated work of zero-clear is necessitated, and further, such a disadvantage has been presented that, even with the renewed zero-clear, it is difficult to zero-set an origin in coincidence with the preceding origin.
Next, there is such a method that, on the main scale, there are provided reference marks in parallel to the length-measuring slit row separately of the length-measuring slit row, and, on the index scale, there are provided marks associated therewith for sensing the reference marks separately of the length-measuring gate slit row, whereby the reference mark is detected by this associated mark and the position thus detected is made to be the absolute origin.
The absolute origin is accurately obtainable by this method. However, a multiplicity of reference marks are arranged along the length-measuring slit row, and at the time of actual measurement, an associated mark of the index scale is superposed on one of the plurality of reference marks, whereby the reference mark should be read to set an absolute origin. In consequence, it becomes necessary to conduct operations to specify one reference mark from the plurality of reference marks, thus presenting the disadvantage that the absolute origin cannot be easily and quickly set.
Furthermore, as another measure, there is a method described in Japanese Patent Publication No. 40684/1983, wherein a multiplicity of reference marks are provided on the main scale in parallel to the length-measuring slit row. Reference mark selecting switches displaceable along the main scale are provided having one of the reference mark selecting switches previously fixed to a position associated with a desirable reference mark, and when the associated mark on the index scale detects a reference mark and simultaneously the reference mark selecting switch is actuated, the reference mark is set as the absolute origin.
However, even with this method, it beco
REFERENCES:
patent: 4101764 (1978-07-01), Nelle
patent: 4363964 (1982-12-01), Schmitt
patent: 4491928 (1985-01-01), Reichl
patent: 4519140 (1985-05-01), Schmitt
Nagai Ryou
Nagashima Etsuo
Sakamoto Hitoshi
Mitutoyo Mfg. Co. Ltd.
Westin Edward P.
Wieland Charles F.
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