GB2214373A - Angular encoder - Google Patents

Abstract

An encoder device encodes angular position of a rotatable member in relation to a series of fixed switch devices. The rotatable member in the form of a drum 1 is profiled at 4 according to a predetermined binary code for each of a plurality of indexed positions of the drum such that the profiling 4 actuates flexible switch devices 7. A plurality of drums 1 may be rotatably mounted on a shaft 2 and form the numerical read-out display of a meter, such as a gas meter. <IMAGE>

Description

ENCODER The present invention relates to an encoder for encoding angular position in the form of electrical signals, in dependence on the angular position of a rotatable member in relation to a series of fixed switch devices.

The invention finds particular application in relation to the electrical reading of the position of a series of rotatable drums, each bearing numbers or other indicia around its periphery, in order to give a read-out at a remote position according to the position of the drums. Such drum arrangements are commonly employed in meters for measuring the consumption of products such as fluids, for example domestic gas.

In order to carry out the remote reading of meters, such as domestic gas meters, analogue information relating to drum position needs to be converted into electrical signals in the form of digital pulses. The analogue information can be converted into digital form by encoders operating according to either the incremental method or the absolute method.

In both cases the digital information is fed to a microprocessor which in turn produces the appropriate reading at a remote point.

Incremental encoders convert the analogue information given by the rotation of the drum shafts into electrical pulses. One example of an incremental system consists of a magnetically operated switch which is activated by the movement of the drum representing e.g. cubic feet of gas. Each activation increases a remote electronic counter by one digit, corresponding to an increase in gas consumption of one cubic foot. However, incremental encoders, although relatively inexpensive compared with absolute encoders, exhibit a number of undesirable features.

Firstly, they are prone to electrical noise, which can cause extraneous pulses to be counted. These extra counts can only be reconciled after comparing the "true" meter reading with the stored information; i.e. a visual inspection of the meter index reading given by the drums is required. Secondly, in the event of power failure, the encoder becomes inoperative and data is lost. Thirdly, in the event of a meter exchange, reconciliation of the stored information is required.

One solution to. the above mentioned problems is to use absolute encoded indexes. Absolute encoders digitise the whole meter index reading; i.e. each digit of each drum is encoded. The advantage of this method is that it is selfcorrecting, unlike incremental systems. Thus, the problem associated with electrical interference can be overcome by taking and comparing several readings. If these differ by, say, more than one digit then additional readings can be taken.

This can be repeated until the difference in readings is acceptable. Also, in the event of apowerfailure an absolute encoded index maintains coding of the drums. On resumption of power, the meter can then be read with no loss of data.

A further advantage of absolute encoders is that in the event of meter exchanges, reconciliation of the meter reading is not required.

In summary, absolute encoders are self-dorrecting whilst incremental encoders are not.

It is an object of the present invention to provide an improved form of absolute encoder which makes use of flexible switch technology.

From one aspect the invention provides an encoder device encoding angular position in the form of electrical signals in dependence on the angular position of a rotatable member in relation to a series of fixed switch devices wherein the rotatable member is profiled according to a predetermined code for each of a plurality of indexed positions of said rotatable member such that said profiling can actuate said switch devices when located at that indexed position to be encoded and said switch devices are formed as flexible switch structures.

Preferably the predetermined code is a binary code and the rotatable member is in the form of a rotatable drum profiled so as to provide projections according to the required binary format for each indexed angular position of the drum. The flexible switch structures may advantageously comprise conducting contact areas formed on neighbouring insulating sheets at least one of which is flexible, and which are separated from each other by an intermediate insulating sheet apertured in the region each pair of oppositely disposed contact areas on the two outer sheets, whereby pressure applied to a flexibly mounted contact of such a pair causes them to engage and thereby close the switch.Where the invention is employed in relation to meters for measuring the consumption of a product, such as domestic gas, each drum includes or is associated with a peripheral region bearing a series of visually readable numerals or other indicia each corresponding to one of the indexed angular positions of the drum which is to be encoded. In a preferred embodiment a decade of numbers 0 to 9 are disposed about the said peripheral region corresponding to ten indexed angular positions, each of which is represented by a discrete binary code.

From another aspect the invention provides an absolute encoder comprising a plurality of such encoder devices in combination with circuit means for producing an absolute encoded I output.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side view of one embodiment of encoder device according to the invention Figs. 2a and 2b show side and end views respectively, to a larger scale, of one of the rotatable drums Fig 3 is an "unrolled" view of the arrangement of the profiling on the periphery of a drum Fig. 4 is a sectional diagram illustrating a flexible switch; and Fig. 5 illustrates a matrix wiring diagram for the four binary encoded drums of Fig. 1.

The encoder devices to be described comprise a series of rotatable drums disposed side by side for rotation about a common axis and each bearing a series of numbers, more specifically a decade, about their periphery. Such an arrangement may form the numerical read-out display of a meter such as a gas meter.

The invention also employs so-called flexible switch technology in which the contacts of a switch are formed as oppositely disposed conducting areas on two neighbouring insulating layers separated by a thin intermediate insulating layer which is apertured in the region of the contacts. At least one of the neighbouring insulting layers is flexible so-that when pressure is applied to it in the region of a contact, the switch contacts are urged together to close the switch.

Referring now to the drawings, the embodiment of encoder device illustrated forms the numerical read-out display of a gas meter and comprises four drums ldisposed side by side and mounted for rotation about a common shaft 2. Each drum comprises an indicating portion 3 consisting of the digits o to 9 regularly spaced around its periphery and an encoding portion consisting of a series of projections or cams 4 arranged in a binary word or format. One binary format corresponds to each of the ten digits 0 to 9.

The preferred binary coding for the projections is shown in Fig. 3 which illustrates the periphery of one of the drums "unrolled". As can be seen, each binary word or format has four bit positions, the raised projections or cams 4 corresponding to a logic 1 and the lower positions i.e. the plain surface of the drum, corresponding to a logic 0.

The shaft 2 carrying the four drums is mounted in a frame 5 which includes a raised platform 6 on which are located four groups G1 to G4 of flexible switches, one group being adjacent each drum. There are four flexible switches 7 in each group and one switch corresponds to each binary bit position on the drum, so that that switch will be actuated by any projections on the drum which are located in that bit position. The platform 6 is adjustable in height to ensure the effective operation of those switches 7 which are engaged by projections 4.

As shown more clearly in Fig. 2 the drums 1 are interconnected in a known manner for stepping round in a decade sequence by means of the sprockets 8 interengaging with gear teeth 9 provided on the end of each drum. The input drive to the device is via the gear 10 and associated spring plunger 11 and cam 12 arrangement. This arrangement is provided to ensure that the projections 4 cannot come to rest between indexed positions, thereby avoiding the possibility of erroneous readings. The cam 12 serves to compress the spring plunger 11 as the cam rotates and prior to the roll-over of any of the digits from one indexed position to the next, the spring is released which ensures a positive changeover from one digit to the next and hence a correct binary read-out from the cam projections and associated flexible switch group.

The binary word configuration of the projections 4 for each of the digits 0 to 9 corresponds to that given in Table 1 below. This word configuration has been chosen because it enables the drums to be moulded in two parts.

TABLE 1 DECADE BINARY 0 1000 1 1100 2 1110 3 1111 4 0111 5 0011 6 0001 7 0110 8 0100 9 0010 Fig. 4 is a sectional diagram illustrating the principle of the flexible switches used in the encoder device. Each switch consists of two neighbouring layers 13 and 14 of insulating material bearing oppositely disposed contacts 15 which may be formed by screened ink or printed circuit techniques. The layers 13,14 are separated by an intermediate insulating layer 16 which is apertured at 17 in the region of the contact areas.

At least the layer 13 is flexible so that when pressure is applied to it in the region of the contacts 15 by one of the projections 4 on a drum 1, the contacts 15 are urged together to close the switch.

The on/off state of each flexible switch in each of the groups switch. Gl to G4 is monitored by an integrated circuit which may be mounted on the device, in order to produce an output electical signal in binary format. In order to minimise the number of connections to the integrated circuit from the switches a matrix wiring arrangement is used i.e. common significant switches are connected together as shown in Fig. 5.

The integrated circuit energises each group G1 to G4 of flexible switches sequentially by applying a voltage of +5 volts to the common line of each group of four switches in turn. The state of the input lines is monitored for the presence or absence of the +5 volt signal. In this way the readings of the indexed positions of the drums are encoded.

This data is then output on demand in any desired manner, for example in serial ASCII format to a remote decoding/reading device.

With such an arrangement a meter can, for example, be read remotely by a hand held unit which stores the serially, transmitted, coded reading. This information can later be down loaded into a main frame computer for record purposes and for automated billing in the case of a consumers meter.

It will thus be seen that with the arrangement according to the present invention, a reading is always possible and there is no time period during the rotation of any drum when a reading cannot be obtained. Although four drums have been shown, clearly any other number of drums and associated encoder devices can be provided.

The absolute encoder according to this invention, has the advantages of small cost and the ability to produce a sealed flexible switch construction which is not prone to long term corrosion problems.

It particularly finds application where: (a) accurate readings are necessary; and (b) where "null readings" are undesirable. For example: (1) Door step meter reading. A reading can be made using a hand held unit. The reading can then be down loaded onto a main frame computer for automatic billing.

(2) Remote meter reading where, for example, information is transmitted down telephone lines.

(3) For use with electronic token meters. In this application the absolute encoded index transmits the reading to the electronic meter where the appropriate charges can be calculated.

Although the invention has been specifically described in association with gas meters, it will be understood that it may be applied to a wide variety of other meters and analogous devices.

Claims (14)

1. An encoder device encoding angular position in the form of electrical signals in dependence of the angular position of a rotatable member in relation to a series of fixed switch devices, wherein the rotatable member is profiled according to a predetermined code for each of a plurality of indexed positions of said rotatable member such that said profiling can actuate said switch devices when located at that indexed position to be encoded and said switch devices are formed as flexible switch devices.

2. An encoder device as claimed in claim 1, in which the predetermined code is a binary code.

3. An encoder device as claimed in claim 2, in which the rotatable member is in the form of a rotatable drum profiled so as to provide projections according to the required binary word or format for each indexed angular position of the drum.

4. An encoder device as claimed in claim 3, in which the drum is provided with a peripheral region bearing a series of visually readable numbers or other indicia each corresponding to one of the indexed positions of the drum which is to be encoded.

5. An encoder device as claimed in claim 4, in which the peripheral region of the drum bears a decade of numbers 0 to 9 corresponding to ten indexed positions, each of which is represented by a discrete binary code.

6. An encoder device as claimed in any preceding claim, in which each flexible switch device comprises oppositely disposed conducting contacts on two neighbouring insulating layers separated by an intermediate insulating layer which is apertured in the region of the contacts,'at least one of said neighbouring layers being flexible such that pressure applied to it in the region of the switch contacts urges the contacts together to a switch-closed position.

7. An absolute encoder comprising a plurality of encoder devices as claimed in any preceding claim in combination with circuit means for producing an absolute encoded output.

8. An absolute encoder as claimed in claim 7, comprising a plurality of encoder devices as claimed in any of claims 3 to 5, in which the drums are mounted side by side for rotation about a common axis of rotation and a group of flexible switch devices is associated with each drum, the number of switch devices in each group corresponding to the number of bits in the binary words defining the various indexed positions of the drum, the output from the switch devices being fed to said circuit means to determine the presence or absence of a voltage on a particular line and thereby produce an output representative of the position of the drums.

9. An absolute encoder as claimed in claim 7 or 8, in which the circuit means is an integrated circuit.

10. An absolute encoder as claimed in claim 7,8, or 9, in which the absolute encoder is arranged to produce an output representing a metered quantity.

11. An absolute encoder as claimed in claim 10, in combination with a metering device.

12. An encoder device substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.

13. An absolute encoder substantially as hereinbefore described with reference to the accompanying drawings.

14. A consumers meter including an absolute encoder as claimed in any of claims 7 to 11 or 13.