Position detecting switch

Details Position detecting switch Position detecting switch

1997-09-02

2001-09-18

Donovan, Lincoln (Department: 2832)

Electrical resistors

Mechanically variable

Movable contact electrically adjustable over length of...

C338S160000, C338S128000

Reexamination Certificate

active

06292090

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a position detecting switch that detects at which selected position out of predetermined selected positions an object whose position is to be detected is located and outputs the detected result as an analog signal.
2. Description of the Related Art
In an apparatus having a drive mechanism incorporated therein such as a video apparatus and a copying machine, a diversity of switches are employed to detect the position of a driving object. For example, for detecting the rotating angular position of a driving object, a rotary switch is often used.
FIG. 4
is a circuit diagram of a 4-bit output rotary switch with a relationship between the predetermined rotating angular positions of a rotor (not shown) and the corresponding outputs thereof shown together. In
FIG. 4
, reference numeral
2
designates a brush serving as a movable contact that is coupled to the rotor;
3
to
5
, switch patterns serving as fixed contacts formed on a not shown board in annular form;
6
, a pull-up resistor;
7
, an input terminal for inputting a power supply voltage (5 V); and
8
, an output terminal for outputting 4-bit data (A, B, C, D).
Numerals
1
to
11
given at the bottommost position in
FIG. 4
designate the predetermined rotating angular positions of the rotor. For example, when data to be outputted from the output terminal
8
is (1, 1, 1, 1), it is meant that the brush
2
is located at the rotating angular position
1
. When data is changed to (0, 1, 1, 1), it is meant that the brush
2
has moved to the rotating angular position
2
by rotation of the rotor.
Thus, which rotating angular position
1
through
11
the rotor is currently located at can be identified by checking the content of data outputted from the output terminal
8
. As a result, the rotating angular position of the driving object coupled to the rotor can be detected.
However, in the case of the aforementioned conventional example, when the rotary switch must be connected to an analog input port of a microcomputer, a D/A converter must be interposed therebetween, which imposes a problem in terms of promoting cost reduction.
A simple modification of a rotary encoder into an analog output type does not give a decisive solution to the problem, because inexpensive circuit parts such as pull-up resistors cannot be used, so that the number of parts is increased and so is the number of wiring points. When a wide voltage range is required in particular, many expensive circuit parts must be employed, which imposes the problem of an increased cost. It may be noted that such problem of increased cost will be described in detail with reference to
FIG. 2
later.
This problem is not specific to rotational movement type position detecting switches such as rotary switches, but the same problem is addressed for linear movement type position detecting switches as well.
SUMMARY OF THE INVENTION
The invention has been made in view of the aforementioned circumstances. The object of the invention is, therefore, to provide a position detecting switch free from the aforementioned shortcomings.
To achieve the above object, the invention provides a position detecting switch for detecting at which position out of predetermined selected positions an object whose position is to be detected is located and outputting a detected result as an analog signal, wherein a switch circuit comprises: a plurality of voltage dividing elements for dividing a reference voltage applied from an external source through a reference voltage input terminal; a fixed contact having a plurality of metallic patterns formed on a board, the plurality of metallic patterns being partially notched so as to correspond to the predetermined selected positions; and a movable contact being coupled to the object whose position is to be detected and coming in contact with the metallic patterns serving as the fixed contact so as to slide thereon, wherein the switch circuit not only divides the reference voltage at a voltage dividing ratio corresponding to a currently selected position of the object but also outputs the divided voltage as the analog signal, and wherein out of the plurality of voltage dividing elements, voltage dividing elements for switching the voltage dividing ratios are connected in parallel to one another through the fixed contact and the movable contact.


REFERENCES:
patent: 4012710 (1977-03-01), Ward et al.
patent: 4139831 (1979-02-01), Ortlieb et al.
patent: 4314666 (1982-02-01), Schotten
patent: 4352084 (1982-09-01), Graves et al.
patent: 4500866 (1985-02-01), Romann et al.
patent: 4743882 (1988-05-01), Simon
patent: 4868646 (1989-09-01), Tsuji
patent: 5286024 (1994-02-01), Winblad
patent: 5561416 (1996-10-01), Marshall et al.
Wolf, S., Guide to Electronic Measurements and Laboratory Practice, p. 19, 1973.

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