Plural rotary member position encoder having electromagnetically

Details Plural rotary member position encoder having electromagnetically Plural rotary member position encoder having electromagnetically

1995-12-14

1998-08-18

Snow, Walter E.

Electricity: measuring and testing

Magnetic

Displacement

32420725, 32420717, 34087002, 34087031, G01D 520, G01B 714, G01B 730, G08C 1502

Patent

active

057962502

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a method and apparatus for indicating the position of a movable member e.g. a dial, wheel or shaft. For example, the invention may be applied to the determination of the position of the dials in a meter such as a water, gas or electricity meter or to rotary encoders in general.
2. Related Art
In a known rotary encoding system for dials of a meter each dial has a pair of spring wipers that travel over and make contact with a track on an associated printed circuit board as the dial rotates. One of the tracks is continuous and the other is interrupted to define a number of contact pads equal to the number of digits carried by the dial (e.g. 0-9). As each dial rotates the wiper contacts successive pads and completes a circuit on each occasion giving an indication of dial position which can be transmitted to a central monitoring station. To ensure reliability of operation, each dial is required to rotate in indexed steps so that its contact is always with one of the pads, and to cause this to happen each dial is controlled by a "snapper" which causes the dial to snap from one position to another in indexed steps. However, the use of snappers increases the torque needed to operate the mechanism which, in the case of an inferential meter such as a water meter, can significantly impede the operation thereof. Furthermore, this system requires that each set of dials to be monitored should have its own circuit board and associated logic circuits which adds to cost, particularly since the tracks and wipers are usually gold plated to ensure reliability of the contact.
A previous non-contact position sensing mechanism uses magnetostrictive resonators and bias elements for applying a magnetic bias field for indicating the relative positions of two members. In such systems, an interrogating alternating magnetic field is applied when it is desired to read the position of the members, and the positions are determined on the basis of the detected signal, which has been modified by the magnetostrictive resonators in such a way that depends on the relative positions of the bias elements and magnetostrictive resonators themselves. However, these systems must overcome the problem that the amount of interrogating alternating magnetic field which is coupled into the magnetostrictive resonator is proportional to the magnetic bias applied by a bias element, which means that the system will be susceptible to external magnetic fields. These prior art devices and techniques suffer from the further disadvantage that a plurality of magnetostrictive resonators and/or bias elements are required, making construction complex and expensive.
A problem with which this invention is concerned is the position of an angular position sensing system for one or more rotary members that does not require a direct electrical contact with the or each rotary member and is of simple construction.


SUMMARY OF THE INVENTION.

According to a first aspect of the present invention, there is provided an apparatus for indicating the angular position of a rotatable member wherein a field is coupled from input means to output means via an intermediate device the coupling being such that the field in the output means is a function of the angular position of the rotatable member.
According to the invention, there is provided an apparatus for indicating the angular position of a rotatable member, comprising input means for supplying energy to an intermediate device, and output means for receiving energy from said intermediate device in response thereto, the intermediate device having an axis which varies so that the energy received by the output means varies as a function of said angular position.
According to the invention, there is also provided a method of determining the angular position of a rotatable member comprising supplying energy to the input means of such an apparatus, detecting the energy in the output means produced in response thereto, and deriving therefrom said angular pos

REFERENCES:
patent: 3598903 (1971-08-01), Johnson et al.
patent: 4037219 (1977-07-01), Lewis
patent: 4401986 (1983-08-01), Trenkler et al.
patent: 4507639 (1985-03-01), Trenkler et al.
patent: 4737698 (1988-04-01), McMullin et al.
patent: 4829247 (1989-05-01), Wallrafen

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