Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Patent
1985-08-30
1987-01-20
Dobeck, Benjamin
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
318568, 318632, G05B 106
Patent
active
046382321
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for calibrating a positioning system including a control unit from which command value signals are provided to a positioning apparatus intended to position an object against a work surface, the location of the positioning apparatus being sensed and converted to an actual value signal fed back to the control unit for calibrating the system. The invention also relates to an apparatus for carrying out the method.
Pick-and-place machines, drawing machines, machine tools etc have to fullfill high precision demands and to accomplish this precision with conventional methods puts high demands on the mechanical precision at the manufacture and high constructional stiffness which will cause high manufacturing costs.
The present invention relates to a method for gaining high machine precision without requiring equally high demands on the manufacture of the machine and to an apparatus for carrying out the method by means of a computerized procedure only requiring an insignificant amount of manual work.
The method makes it possible to replace precision with repeatability. As it is considerably less expensive to manufacture repeatable machines than Precision machines, the method implies the possibility of gaining the same operational precision of the machine at a low price. Moreover, in many cases there are other advantages. A machine intended to maintain high precision after long and bumpy transport paths often has to be designed as a stronger, and thus a considerably heavy machine. If the moving parts also are made heavy, powerful motors, power amplifiers and power supplies are required to move the displaceable parts.
However, the economical advantages of the method can easily be obviated if the practical way of carrying out the method is complicated, time-consuming or brings about the risk for erroneous input data. The invention also comprises an apparatus for carrying out the method to low costs and without trained operators when the machine has been erected at the customer's. The apparatus is based on the fact that methods for other purposes have been devised for producing two-dimensional objects cheaply and with high dimensional precision, e.g. printed cards and black and white photographic film. The apparatus utilizes the high precision of such objects which can be easily read by a sensor connected to a control unit. It will then be possible for instance to let a computer program in the control unit, apply the method to the apparatus. In this way the method can be applied rapidly, accurately and without mistakes due to carelessness and with a minimum of human interference. The work of the operator is limited to the erection of the apparatus and possible extra sensors, test of the electrodes etc., starting the program and after completed calibration dismantling of the apparatus etc. and if necessary storing the calibration data.
The method of the invention is characterized by the features defined in claim 1 and consists of of a calibrating procedure, where the actual positions expressed in the coordinates of the working area are measured in a sufficiently large number of points by means of a calibrating device comprising a calibration plane and a calibration probe and are compared with the corresponding coordinates as measured with the position detectors contained in the machine (data from e.g. incremental detectors, calculations based on data sent to step motors or the like). The error differences obtained in this way are stored. When the machine later on is used the measured error differences can be utilized to compensate for the main part of the errors of the machine construction and/or of the sensors by way of interpolation.
The apparatus according to the invention is characterized by the features defined in claim 3 and is thus made that the position which is taken in a sequence of movements typical for the working procedure, can be measured automatically and fed back to a control unit (control computer or the like) of the machine. E.g. in a component mounting machine the posi
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patent: 3955072 (1976-05-01), Johannsmeier
patent: 4190889 (1980-02-01), Etoh
patent: 4260187 (1981-04-01), Frosch
patent: 4281385 (1981-07-01), Nakaso et al.
patent: 4562392 (1985-12-01), Davis et al.
Rodin Gunnar
Stridsberg Lennart
Dobeck Benjamin
Mydata Automation AB
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