GB2358063A - An angular position encoder - Google Patents

Abstract

An angular position encoder on printed circuit having circular conductor sectors disposed on two concentric circles, the sectors of each of the circles being connected to the nodes of respective resistor divider networks. Both divider networks are capable of generating two series of increasing electric potential values. Each of the values generated by the first network is comprised between two of the voltage values generated by the second network.

Description

2358063 AN ANGULAR POSITION ENCODER This invention relates to an angular

position encoder on printed circuit. These angular posiflon encoders are generally used to determine the angular position of a shaft by way of a multiple sliding electrical contact coupled to the shaft itself. When the shaft rotates, the multiple contact describes concentric circular paths on a flat surface perpendicular to the shaft, typically a printed circuit, connecting together different conductor areas of said printed circuit, normally arranged on concentric circular sectors The device of the invention is of the potentiometric type, the position of the shaft being encoded by a variable divider of a reference voltage.

is Potentiometric encoding systems on printed circuit formed by a discrete number of circular conductor sectors, each connected to a node of a series connected resistor network, said resistor network being supplied With a reference voltage, are well known. A sliding contact mechanically connected to a shaft sequentially connects each of said circular sectors to a circular conductor coaxial therewith, there being obtained in said circular conductor a variable voltage which acquires a discrete value equal to that of the node connected to the conductor sector then in contact with the sliding contact.

The resistor network may be formed by a deposition of conductor films on the printed circuit, or by means of resistive components of the type generally used in the electronics industry, available with very convenient shapes and accuracy levels and at attractive prices, soldered to conductor islets of the printed circuit, electrically connected to the circular conductor sectors by conductor tracks. The solderable islets, connecting tracks and circular sectors are formed in a common photogravure process.

-2.

The potentiornetric encoding system described has a peculiarity and a limitation which are overcome by the present invention and which are the following:

The obvious peculiarity is that the required number of resistors forming the network is equal to the number of circular sectors into which the stroke of the sliding contact is divided, less one- Thus, if the number of circular sectors is 30, 29 resistors are required to generate 28 discrete voltage values, which when added to the voltages of both poles of the reference voltage source, give 30 selectable values.

The limitation consists of there being certain angles of the sliding contact position where it leaves one conductor sector and contacts the next. Owing to the dimensional limitations of the printed circuit technology and of the contact, situations may arise where there is either no contact or simultaneous contact with two sectors. Normally, it is preferred to space the sectors apart at a prudential distance to avoid the possibility of shortcircuits thereacross, caused by pollution of the insulating surface of the printed circuit with metallic particles entrained by the sliding contact itself, with this spacing apart causing said situation of no- contact The fact that these blind arcs in which the encoder does not deliver information relative to the angular position exist is not a serious drawback when there is a mechanical centring mechanism acting on the shaft. allowing it to occupy exclusively a number of stable selectable positions. In this case, we have a rotatory selector having a discrete number of positions, mechanically bound to positions of the sliding contact in the substantially centred areas of the respective conductor sectors.

However, when the shaft may adopt an infinite number of angular positions, such as is the case of the typical volume control of an audio amplifier, then a serious drawback does exist and, therefore, this encoding method may not be used.

The invention proposes overcoming these drawbacks. This object is achieved by an angular position encoder on printed circuit that is provided with circular conductor sectors disposed on first and second concentric circles, the sectors of each -. - of said circles being connected to the nodes of respective resistive divider networks, said two diTider networks being capable of generating two series of increasing electric potential values, each of said values generated by the first network being comprised between two of the voltage values generated s by the second network.

The invention solves the problem explained, at the same time as it uses a much lower number of resistors, for example, in the case of a 32 position encoder, the number of resistors is reduced from 31 to 18.

Generally speaking, the number of resistors required for a resolution lo of N angular positions is (N12) + 2.

The method consists of arranging the resistors in two networks, called first and second network, each network having N/4 + 1 resistors in series, or the immediately higher whole number, supplied with one same reference voltage, the values of all the resistors being the same, except for is the two resistors occupying the initial and end positions of the first network.

If R is the resistive value of all the other resistors, the preferred value for the first and last resistors of the first network will be 0.5R and 1.5R, respectively.

Dependling on the number of positions to be discriminated, the number of resistors of one network or the other may vary by one, the preferred value of both end resistors being, in this case, 0.5R.

The angular position encoder is preferably provided with a conductor ring disposed on a third circle concentric with the first and second circles.

The angular position encoder is also advantageously provided with a rotatory sliding contact having three or more contacts capable of causing a short-circuit on three respective angular positions located on each of said three first, second and third concentric circles.

Preferably also. the sliding contact is constructed in such a way that two or three of said angular positions are always aligned on one same radius of the circles.

Preferably, each of the conductor sectors of the first and second circles extends over an arc from two to three times longer than the arc comprised between two consecutive sectors on one of said circles and preferably the conductor sectors disposed on the first circle are angularly interspaced between the sectors disposed on the second circle- The resistor networks are advantageously formed by surface 5 mounted microresistors.

The first, second and third circles are preferably concentric and are situated on a plane perpendicular to a shaft of plastics material fixedly attached to a programme selector control of a domestic washing machine.

Said shaft is advantageously provided with a mechanical centring lo device formed by a rnetal ball sliding in a bore aligned with a radius of the shaft. which is urged by a spring against the inner surface of a hollow cylinder coaxial with said shaft, said inner surface of the coaxial hollow shaft having an internal toothing with 30 cylindrical housings of a radius similar to that of said ball.

is Finally, said inner surface of the coaxial hollow cylinder may advantageously rotate about its axis driven by a geared motor coupled to a crown gear fixedly attached to said inner surface of the hollow cylinder.

An example of the present invention will now be described in detail with reference to the accompanying Figure.

Figure 1 is a wiring diagram of an angular position encoder according to the invention.

If Vref is the reference voltage applied to the resistor networks, M the ordinal number of each node, starting out from the one closest to the reference voltage negative terminal, the voitages Vm obtained at the N/4 nodes of the second network would be:

Vrn = (VI(N14 +1)) x M Thus, for a 32-position encoder, such as the one shown schernatically in Figure 1, there will be provided a second network of 3214 +1= 9 equal resistors and the following intermediate voltages are obtained:

VIV111 = V/9 VIV12= 2V/9 VIV118= 8V/9 If S is the ordinal number of each node of the first network, the voltage Vs obtained at each node of the first network is as follows:

Vs= (VI(N14+1)) x (2S-1)12 In the case of 32 positions.

VS11= V19XY2= 0.5V/9 VS2= V/9 x 312 = 1.5V/9 VS8= V/9 x 1512 = 7.5V/9 In other words, the voltages obtained at the nodes of the first network are exactly intermediate to those obtained at the nodes of the second network.

For designing the angular encoder, there are disposed an a printed circuit two series of coaxial circular sectors of N14 circular sectors each, siluated on two concentric circles respectively, with an angular separation between sectors of one same series equivalent to one third of the are thereof, the sectors of the first and second circles being offset by two thirds of the arc of a sector.

In the case of 32 positions, there are disposed, therefore, on two concentric circles 8 plus 8 =nductor sectors of 36018 x 314 = 33.750, separated by insulating arcs of 11-250.

The sectors on the first circle (preferably the outer circle) preferably extend over the following arcs:

A: Froni -11.251 to 22.511 B: From 33.750 to 67.750 C: From 78.750 to 112.50 D. From 123.750 to 157.50 E:From 168.750 to 202.50 F: From 213.750 to 247.50 G From 258.750 to 292-50 H. From 303.750 to 337. 50 The conductor sectors on the second circle (preferably the inner circle) extend over the following arcs: 1: From 11.250 to 450 J: From 56. 251 to 900 K: From 101.250 to 1350 L: From 146.2513 to 1800 M. From 191.251' to 2250 N: From 236.250 to 2700 0. From 281.250 to 3150 P: From 326.2511 to 00 The arcs of the first circle (outer circle) are connected successively to the nodes of the first resistor network, connecting the first sector A to the node having the lowest voltage VS1, up to H to the node having the highest voltage VS8.

The arcs of the second circle (inner circle) are connected successively to the nodes of the second resistor network. connecting the first sector 1 to the node having the lowest voltage VIV11, up to P to the node having the highest voltage VIV18.

A 360 ring is disposed concentric to the other two circles, preferably in the interior thereof.

The sliding contact C attached to the shaft the position of which is to be encoded will be formed by a multiple contact, preferably aligned on a radius, which will slide on the printed circuit, with each individual contact describing a concentric circle. The position of said contacts will be designed to coincide with the circles on which the two series of conductor sectors have been positioned. connecting two points of both circles where bath series of sectors have been situated with some point on the inner 36011 s sector, on which the resulting voltage V will be measured.

Alternatively, the encoder may be disposed in linear fashion, the circular sectors becoming segments.

In Figure 1 the sectors or segments and the connections described have been shown in linear form, for greater ease of understanding.

In view of the peculiar arrangement of the conductor sectors along the whole angular or linear path of the sliding contact, the following situations of connection with the inner ring occur 1.- A 'IT- E 2.- 1 + A 18.- M + E 1-1 19._ m 4.-11 + B 20.- M + F 5._ a 21.- F 6.- J + B 22.- N + F T- J 21- N 8.-J + c 24.- N + G 9._ c 25.- G 10.- K+ C 26.- 0 + G 111.- K 27.-0 12.- K+ D 28.- 0 + H 11- D 29.- H 14.- L+ D 30.- P + H 15.- L 31._ P M- L+ E 31- P + A It is obvious that on the odd-numbered arcs the voltage measured on the inner ring will coincide with that of the sole inner or outer arc connected.

On the even-numbered arcs, on the other hand, a short-circuit will occur across a node of the first resistor network and a node of the second network. there being obtained an intermediate voltage which is fully s predictable by applying the law of superimposition of networks or, in particular, Thevenin's theorem.

Since the voltages across overlapped sectors are relatively closely and the impedance networks very similar, the resulting voltage is very close approximate to the mathematical mean of both voltages of the sectors in io open circuit.

In this way, starting out from the N/2 node voltages, generated by N12+2 resistors, N discrete, different equidistant voltages are obtained which change every 360/N degrees without any interruption. The only break in the voltage occurs on the Ocl position where the voltage goes from 15 minimum to maximum.

Claims (11)

1 An angular position encoder on printed circuit, the encoder being provided with circular conductor sectors disposed on first and second concentric circles, the sectors of each of said circles being connected to the nodes of respective resistive divider networks, said two divider networks being capable of generating two series of increasing electric potential values, each of said values generated by the first network being comprised between two of the voltage values generated by the second network.

2.- The angular position encoder on printed circuit according to claim 1, characterized in that it is provided with a conductor ring disposed on a third circle concentric with said first and second circles.

3-- The angular position encoder an printed circuit according to claim 1 or claim 2, characterized in that it is provided with a rotatory sliding contact having three or more contacts capable of causing a short- circuit across three respective angular positions located on each of said three first, second and third circles.

4-- The angular position encoder on printed circuit according to at least one of claims 1 to 3, characterized in that the sliding contact is constructed in such a way that two or three of the said angular positions are always aligned on one same nadius of the circles.

5.- The angular position encoder on phrited circuit according to at least one of claims 1 to 3, characterized in that each of the conductor sectors of the first and second circles extends over an arc from two to three times longer than the arc comprised between two consecutive sectors on one of said.circles.

6,- The angular position encoder on printed circuit according to at least one of claims 1 to 5, characterized in that the conductor sectors disposed on the first circle are angularly interspaced between the sectors disposed an the second circle.

-10.

7.- The angular position encoder on printed circuit according to at least one of claims 1 to 6, characterized in that the resistor networks are made with surface mounted microresistors.

8.- The angular position encoder on printed circuit according to at Ileast one of claims 1 to 7, characterized in that the first, second and third circles are concentric and are situated on a plane perpendicular to a shaft of plastics material fixedly attached to a programme selector control of a dornestic washing machine.

g.- The angular position encoder on printed circuit according to lo at least one of claims 1 to 8, characterized in that said shaft is provided with a mechanical centring device formed by a met& ball sliding alorig a bore aligned with a radius of the shaft, which is urged by a spring against the inner surface of a hollow cylinder cowdal with said shaft, said inner surface of the coaxial hollow cylinder having an internal toothing With 30 cylindrical is housings of a radius similar to that of said ball.

10.- The angular position encoder on printed circuit according to at least one of claims 1 to 9, characterized in that said inner surface of the coaxial hollow cylinder may advantageously rotate about its axis driven by a geared motor coupled to a crown gear fixedly attached to said inner surface of the hollow cylinder

11. An angular position encoder substantially as shown in andlor described with reference to the accompanying drawing.