Electronic caliper using a reduced offset induced current position transducer

Abstract

An electronic caliper having a reduced offset position transducer that uses two sets of coupling loops on a scale to inductively couple a transmitter winding on a read head on a slide to one or more receiver windings on the read head. The transmitter winding generates a primary magnetic field. The transmitter winding is inductively coupled to first loop portions of first and second sets of coupling loops by a magnetic field. Second loop portions of the first and second sets of coupling loops are interleaved and generate secondary magnetic fields. A receiver winding is formed in a periodic pattern of alternating polarity loops and is inductively coupled to the second loop portions of the first and second sets of coupling loops by the secondary magnetic fields. Depending on the relative position between the read head and the scale, each polarity loop of the receiver winding is inductively coupled to a second loop portion of either the first or second set of coupling loops. The relative positions of the first and second loop portions of the first and second sets of coupling loops are periodic and dependent on the relative position of the coupling loops on the scale.

Description

BACKGROUND OF THE INVENTION1. Field of InventionThis invention relates to an electronic caliper. More particularly this invention is directed to electronic calipers using a reduced offset induced current position transducer.2. Description of Related ArtU.S. patent application Ser. No. 08 / 645,483 filed May 13, 1996, and incorporated herein in its entirety, discloses an electronic caliper using an inductive position transducer.The operation of the electronic caliper using the inductive position transducer described in the application Ser. No. '483 is generally shown in FIGS. 1, 2, and 3. As shown in FIG. 1, an inductive caliper 100 includes an elongated beam 102. The elongated beam 102 is a rigid or semi-rigid bar having a generally rectangular cross section. A groove 106 is formed in an upper surface of the elongated beam 102. An elongated measuring scale 104 is rigidly bonded to the elongated beam 102 in the groove 106. The groove 106 is formed in the beam 102 at a depth about equal...

AI Technical Summary

Benefits of technology

This invention provides an electronic caliper using an induced current position transducer with improved winding configurations. The improved winding configurations increase the proportion of the useful output signal component relative to extraneous ("offset") components of the output signal without requiring increased transducer fabrication accuracy. Furthermore, the winding configurations provide means to enhance the degree of output signal change per unit of displacement for a given measuring range.

This is accomplished by winding configurations that minimize and nullify the direct coupling between the transmitter and receiver windings while providing enhanced position-dependent coupling between them through a plurality of coupling windings on the scale which interact with a plurality of spatial modulations of the windings.

In a first embodiment of the electronic caliper using the induced current position transducer of this invention, the transmitter winding is divided into a first transmitter loop and a second transmitter loop, with the first transmitter loop placed on one side of the receiver windings and the second transmitter loop placed on the other side of the receiver windings. The magnetic fields created by the first and second loops of the transmitter winding counteract each other in the area of the receiver winding. This minimizes the extraneous effects of any direct coupling from the transmitter winding to the receiver winding.

These winding configurations substantially eliminate several extraneous signal components, resulting in simplified signal processing and improved transducer accuracy and robustness in an economical design.

Problems solved by technology

This offset V.sub.o is an extraneous signal component that complicates signal processing and leads to undesirable position measurement errors.

Experience in manufacturing a transducer indicates it is practically impossible to eliminate this source of error from the induced current position transducer of a conventional caliper.

Such extraneous signals complicate the required signal processing circuitry and otherwise lead to errors which compromise the accuracy of the transducer.

However, the effectiveness of this technique alone depends on the degree of separation between the transmitter and receiver windings.

Hence, this technique contradicts the need for high accuracy linear caliper of compact size.

However, this technique leads to additional complexity, cost, and sensitivity to external fields, in a practical device.

Furthermore, the simple winding configurations disclosed in association with these techniques include no means for creating a device with a measuring range significantly exceeding the span of the transmitter and receive windings.

In addition, the simple winding configurations provide no means for significantly enhancing the degree of output signal change per unit of displacement for a given measuring range.

Thus, the practical measuring resolution of these devices is limited for a given measuring range.

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