Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1993-01-01
1994-07-05
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
33558, G01N 2186
Patent
active
053269829
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an analogue sensor.
For precision measurement of mechanical components, e.g. coordinate measuring machines, various types of measuring probes are used. The most common type is based on the principle that a current contact path is broken if the tip of the probe, which often has the shape of a ball, is moved in any direction (x, y, z) by striking an object, thus overcoming a certain spring force, whereupon a current path is broken and the measured value is read instantaneously. More precise measuring machines are based on the principle of arranging a number of differential transformers, e.g. three, so that they, with the aid of linkage arms, can measure movements in an analogue manner in the x-, y- and z-directions. This provides the advantages that striking forces are eliminated and deviation can occur over a certain period of time (integrated). This increases the accuracy of the measured value.
Such probes are, however, expensive and complicated in their construction. They also have relatively heavy masses in the sensing portion, and the measuring speed is thus low, which means that the entire measuring system will have a relatively low total measuring capacity. Good measuring capacity together with measuring quality is very essential for a measuring system of this type.
The main purpose of the invention is to increase the measuring precision and to reduce the mass of the moving components of a probe as well as substantially increasing the capacity of the measuring machine, in an application, in which the probe is functioning as a measuring system of its own in the measuring machine system.
The PCT-application having the International Publication Number WO 90/00717 describes a probe for a position-determining apparatus including a stylus which is suspended rotational around a point of rotation in a low-friction support. Coordinate measurements in only two dimensions can be achieved. The angular deviation of the stylus caused by touching an obstacle is measured by an optical measurement arrangement. The possibility of having an auxiliary force supply is briefly mentioned.
A first main object of the invention is to provide an analogue sensor for three-dimensional measurements functioning as a measuring system of its own.
A second main object of the invention is to provide a functional force supplier for use in an analogue sensor.
A third main object of the invention is to provide a measuring arrangement for measuring an object which combines mechanical measuring and optical measuring in a single measuring head.
According to the solution of the first object the stick is suspended floatingly such that it can rotate around a rotation center but that the rotation center can move in a direction axial to the probe. In order to achieve this the stick is either suspended in a spring means or free floating in a device held in the space by a magnetic free hovering arrangement. based on the variation of capacitance is demodulated without phase shift and is filtered. The moveable element or elements can as an alternative change places with the fixed elements, so that the moveable elements will be the driving elements.
DESCRIPTION OF THE FIGURES
According to the solution of the second object the force supplier is adapted to a probe in a coordinate measuring machine, said probe having an analogue sensor including a sensing part, sensed by said sensor when a sensing element coupled to the movable sensing part touches an obstacle and is thus displaced, including a force supplier portion fixedly connected to the movable sensing part of the sensor and a second force supplier portion fixedly connected to the stationary sensing part of the sensor and by control means providing electrical control signals to said force supplying arrangement to set said sensor in a required form of displacement, and is characterized by control means providing electrical control signals to said force supplying arrangement to set said sensor in a required form of displacement, said control means being fed with the
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patent: 4521973 (1985-06-01), Wiklund et al.
patent: 4896110 (1990-01-01), Shimizu et al.
patent: 4972597 (1990-11-01), Kadosaki et al.
patent: 5012591 (1991-05-01), Asakawa
patent: 5058433 (1991-10-01), Wilson et al.
Geotronics AB
Nelms David C.
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