Geometrical instruments – Distance measuring – Opposed contacts
Reexamination Certificate
1999-11-08
2001-12-25
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Distance measuring
Opposed contacts
C033S708000
Reexamination Certificate
active
06332278
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a portable precision caliper, or slide gauge, used for measuring linear dimensions. More specifically, the present invention relates to a portable precision caliper of an electronic type.
2. Related Art
Traditional vernier calipers tend to be gradually supplanted by electronic calipers which afford better reading at a competitive price. Most of the electronic calipers commonly used nowadays incorporate capacitive sensors. The variations in capacitance caused between an array of electrodes on the caliper's shaft and an array of electrodes disposed opposite on the caliper's slide are measured so as to supply information depending on the position of the slide along the shaft. This information is displayed on a screen, usually integral with the slide. Circuits of this type are described, for example, in patent application EP96810686 in the name of Brown & Sharpe TESA SA.
The principle of capacitive measuring has established itself on the one hand because it provides excellent resolution and precision, and on the other hand because the electricity consumption of these devices is very low, so that they can be powered by a battery for example. Such sensor calipers of a capacitive type must however be kept clean for them to function properly. They are thus badly suited to functioning in a humid environment or an environment subjected to splashes of lubricant or to dust for example. In such difficult conditions, hand-operated vernier calipers or watch-type calipers are therefore preferred to electronic calipers.
Document EP286820 describes a caliper comprising a scale fitted with magnetized sections. A magnetic reading head is fitted on the slide and records the variations in magnetic field caused by the displacement of the slide. Such a magnetic head is however relatively costly and voluminous, so that it is difficult to integrate it within the reduced volume of a caliper. The accuracy of measurement depends directly on the precision and noise in the magnetic head as well as on the correct positioning of the head in relation to the scale. Furthermore, the resolution afforded by this device is limited.
One object of the present invention is therefore to propose a portable electronic caliper which is improved with respect to the prior art devices. In particular, an object of the present invention is to propose a caliper comprising a sensor with a low sensitivity to dust and lubricants, providing a resolution on the order of a hundredth of millimeter and an accuracy on the order of a few hundredths of millimeter, that is, a performance which is comparable to that afforded by capacitive calipers at similar cost, and with an electricity consumption sufficiently reduced so as to be able to be powered by a simple battery, for example by a lithium battery.
SUMMARY OF THE INVENTION
According to the invention, these objects are attained by means of a portable electronic precision caliper comprising a shaft fitted with a magnetized scale having a period of magnetization &lgr;, a slide which can be displaced longitudinally along said shaft, the slide and the shaft being each fitted with a jaw, an electronic circuit fitted on said slide and self-powered, said electronic circuit comprising a single sensor, said sensor being equipped with an array of n magnetoresistive electrodes disposed opposite said scale so that the values of the resistances of the magnetoresistive electrodes are a function of their longitudinal position along the scale, n being greater than two, said electronic circuit making it possible to determine, from the values of resistance of the magnetoresistive electrodes, information depending on the gap between said jaws and to display this information on an electronic display.
The caliper's shaft according to the invention is fitted with a magnetized scale having a period of magnetization &lgr;. The sensor is equipped with an array of magnetoresistive electrodes disposed opposite said scale so that the values of resistance of the magnetoresistive electrodes are a periodic function of the longitudinal position of the sensor along the scale. The number of magnetoresistive electrodes is large, in any case greater than 2. Means make it possible to determine, from the values of resistance of the magnetoresistive electrodes, information depending on the gap between the jaws of the calipers. This information is displayed on an electronic display.
Sensors with magnetoresistive electrodes for measuring linear or angular dimensions are known as such. The resistance of the magnetoresistive electrodes of the known sensors is however too weak for them to be able to be powered by a battery. Use of these sensors with a high electricity consumption in electrically self-powered apparatus, for example in portable precision calipers, has therefore not been contemplated.
Calipers using the properties of magnetoresistive materials have already been described for example in patent documents U.S. Pat. Nos. 5,029,402, 4,226,024 and 5,174,041. These documents describe calipers equipped with two distinct sensors, each comprising one magnetoresistive electrode. The distance between the two sensors is critical and determines the achieved accuracy of measurement. The principle adopted using only two magnetoresistive electrodes does not make possible the construction of precision calipers, that is, of calipers which are able to measure lengths with an accuracy and a resolution less than 0.1 mm. For these reasons, use of these calipers is reserved to specific applications such as for measuring meat pieces of the diameter of tree trunks, for which the required accuracy is not very critical. The teachings of these documents however cannot be transposed to the very different technical domain of precision measuring.
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Bezinge Alex
Bolli Jean-Luc
Bennett G. Bradley
Brown & Sharpe Tesa SA
Pillsbury & Winthrop LLP
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