Optics: measuring and testing – Angle measuring or angular axial alignment – With photodetection remote from measured angle
Patent
1982-02-22
1984-12-04
Buczinski, S. C.
Optics: measuring and testing
Angle measuring or angular axial alignment
With photodetection remote from measured angle
250226, 250227, 356141, 356400, G01B 1126
Patent
active
044860951
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to movement measuring apparatus and landmarks for use therewith. The invention can be used for measuring, recording and monitoring human motion in for example biomechanics, bioengineering and the study of motor skills in physiological psychology. In such applications landmarks are affixed to physical elements whose movement is to be measured. The invention can be used also to record contours by affixing the landmark to a wand or probe and moving the landmark across the physical element whose shape is to be recorded. The invention could also be used to program and control robots and similar manipulative machines. The versatility of movement measuring apparatus of the invention may permit other applications.
BACKGROUND OF INVENTION
The inventor has previously described a movement measuring apparatus referred to as CODA (see Mitchelson, D. L. 1975): Non-photographic techniques for movement analysis; in: Grieve, D. W. et al. Techniques for the analysis of human movement. Lepus, London; and Mitchelson, D. L. (1979): Bioengineering in motor function assessment and therapy; and in: Progress in Stroke Research, pp. 117-124. Ed. Greenhalgh, R. M. Clifford Rose, F. Pitman Medical, London.).
In such apparatus' landmarks were used in the form of LED's (light emitting diodes) which could be pulsed or modulated for distinguishing one landmark from another. Light impinging on multiple photodiode detector plates produced an analogue/digital signal indicative of the angular position of the LED landmark in the multiples photodiode observation field. The multiple photodiodes mounted on a plate were costly and the plate position had to be carefully calibrated to ensure reproducibility. The signal was a position-dependent signal and the accuracy of measurement obtainable was hence limited. The apparatus was costly and required skilled operatives.
There is also known a so-called SELSPOT system (made by Selective Electronic Company of Molndal Sweden) using LED landmarks but a single multiple electrode photodiode producing an entirely analogue signal dependant on the horizontal and vertical position of the landmark in an observation field. Ambient light could influence measurements. Where 3-dimensional measurement is required separate measuring units have to be sited carefully in their appropriate relative positions. Again the apparatus was costly, difficult to use and liable to produce inaccurate or not reproducible results.
It is the object of the invention to provide a movement measuring apparatus which can improve on the aforementioned apparatus as regards manufacturing cost, ease of use, accuracy and/or reproducibility.
SUMMARY OF INVENTION
According to the invention there is provided a movement measuring system including a measuring apparatus for scanning an observation field and a suitably reflective landmark located in the observation field, said apparatus having:
(a) a means generating a beam of radiation; and a measuring unit comprising:
(b) a moving mirror reflecting the beam to scan the observation field;
(c) a means producing a signal related to the phase of movement of the mirror;
(d) a means producing a landmark detect signal when the landmark reflects radiation onto the mirror; and
(e) a means producing a signal related to the angular position of the landmark in the observation field by reference to the mirror phase signal at the time of a landmark detect signal.
When the landmark reflects back to the moving mirror a signal can be obtained related to the angular position of the landmark in the field. The system is basically a scanning system. Because only the phase of mirror movement needs to be determined, the electronic arrangement can be relatively simple. No wires need to be connected to subjects under examination.
The landmark may be a single or a plurality of retro-reflecting objects. Suitably the retro-reflecting object has a plurality of reflecting surfaces at a 90.degree. angle so as to retro-reflect in a wide range of angles of incident radiation.
The landm
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Buczinski S. C.
Movement Techniques Limited
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