GB1563748A - Keyblocks - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO KEYBLOCKS (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company, of 190 Strand, London W.C.2.

England. do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a keyblock or push-button unit in which the selection of one of a set of annotated buttons causes the generation of a unique code which may be subsequently identified by man or machine.

It is particularly suitable for, but not restricted, to man-machine interfaces requiring the selection and coding of alphanumerics, and the invention will be described in its application to a keyblock used on a telephone set for sending wanted number information.

Such keyblocks normally require the user to select serially from ten or twelve numerics and symbols, and in current exchanges, causes the sending of either a series of pulse trains varying from one to ten in length or a series of audio frequency tones transmitted in pairs. The buttons of such a keyblock are arranged as a 3 x 4 coordinate matrix, and in current keyblocks, each button is either associated with an individual 'make' switch (total of 12 switches), or by mechanical or electrical means, 'make' switches are associated with each row and each column (total of 7 switches). In both types the switches may be connected so that all switches have one side common giving respectively a l-out-of-12 selection, or a (I-out-of-3 + l-out-of-4) selection, taken 2 at a time.Alternatively, the switches may be matrix connected so that each button gives a contact between the column and row co-ordinate corresponding to its position. By strobing the rows or columns in sequence, simple logic can determine which button has been depressed. In addition to the particular contact operation associated with each button, there may also be "common bar" contacts which operate regardless of which button is depressed.

To ensure maximum comfort and ease of operation to the user, it is desirable to minimise any variation of operating forces between the buttons of any keyblock, so if mechanical operation is required, coding patterns requiring the operation of the same number of contacts behind each button have generally been used. It is an object of this invention to enable non-symmetrical coding to be used.

According to the present invention there is provided a push-button set which includes a co-ordinate matrix of push-buttons each of which when depressed causes the generation of a code combination individual to the depressed push-button, which push-button set includes first and second sets of light pipes extending parallel to the rows and columns respectively of said push-buttons and so arranged that each said push-button is aligned with two of said pipes, one for that button's row and one for that button's column, wherein each said light pipe is arranged to traverse two of said rows or two of said columns, wherein each said light pipe is served at one of its ends by a light source and at the other of its ends by a light detector, and wherein the depression of one of said push-buttons blocks the passage of light along at least two of said pipes, one of which belongs to the push-button's row and one to the push-button's column, so that when a said push-button is depressed the passage of light is blocked in a combination of said pipes individual to the depressed push-button.

It can be shown that a greater number ofcode combinations can be achieved if codes allocated to the individual operating buttons are not restricted to selecting one or two at a time, but may embrace any number at a time, see Table 1.

TABLE I Combinations Obtainable from Selection Combinations Selectable Variations 1 at a time 2 at a time random at a time s 2 2 1 3 3 3 3 7 4 4 6 15 5 5 10 31 6 6 15 63 The above table shows that only four variables are required to achieve the twelve different codes for a push-button keyblock as used in telephony.

In our Co-pending Application No.

27982/76 (Serial No. 1540249) we havedescribed and claimed the use of light sources and detectors connected by straight light tubes to achieve a contactless keyblock. If applied to a 12-button keyblock for a telephone, a total of 7 light sources and 7 detectors would be required, although by the use of light-pipes either all light sources or all detectors could be combined into a single-unit.

Embodiments of the invention will now be described with reference to the drawings accompanying the Provisional Specification in which Fig. 1 is a schematic representation of a telephone keyboard embodying the present invention Fig. 2 is a timing diagram.

Fig. 3 is a schematic representation of a 16 button keyboard embodying the present invention.

Fig. 4 is a top plan view of a telephone keyblock embodying the invention.

Fig. 5 is a section along the line X-X of Fig. 4.

Figure 1 shows diagrammatically a keyblock illustrative of the invention. By the use of light pipes 1, 2, 3,4 each light beam is made to travel through at least two rows of columns and the depression of a button located adjacent to each row/column intersection determines the code transmitted by blocking off the light in both directions. The coding pattern inherent in the keyblock may be extracted by various means and allows a design choice, according to whether the objective is to achieve mechanical or electronic simplicity, or to provide maximum protection against error. For convenience the coding patterns relate to the cutting off of a particular ray of light and it is assumed that in the idle state all light paths are open.

In a first arrangement the light sources at Column B and Row X are illuminated simultaneously from the light sources associated with Column B and Row X. Such a system is very simple mechanically, and a very simple code translation can be used to associate the digits with the recommended MF signalling system known as SSMF No. 4 in the UK and being internationally recommended by C.E.P.T. and C.C.I.T.T.

As the light sources do not require to be strobed it is possible to employ nuclear or other light sources, not subject to electronic control.

Table 2 below, gives the association of digit and coding pattern.

TABLE 2 Coding Pattern for 12-Digit Keyblock

Digit Coding Pattern from Detectors A C W Y 1 X X 2 X X X 3 X X 4 X X X 5 X X X X 6 X X X x X 8 X X X 9 X X * X O X X x Unused x Codes x x x The system requires two light sources and four detectors and uses very simple light pipes.

In an alternative to the above arrangement, the two light sources are combined using light pipes or reflectors. The coding pattern remains as in Table 2, thus only one light source and four detectors are required.

In another alternative the two light sources are strobed alternately. The repetition rate is not critical and timings indicated in Figure 2 which shows the strobing pulses, are for the sake of illustration only. The output code again remains as in Table 2, but since there is now a time interval between any outputs from Detectors A and C and any output from Detectors W and Y, it is possible to combine optically the outputs of A and W and C and Y respectively to reduce the number of detectors to two.

Even if optical coupling is not practical, there would be some advantage in this mode of operation since the electrical outputs could be combined giving fewer input terminals to a subsequent logic chip.

A further alternative arrangement is in effect the reverse of the first arrangement, i.e. using 4 light sources and two detectors.

The light sources must, of course, be strobed to identify the particular light channels being interrupted. Yet a further alternative is the reverse system to the second-mentioned one, again strobing the light sources in sequence to identify the coding pattern.

The last two alternatives are clearly preferable in a system where light sources are cheaper than detectors.

Although the invention has been described using a 12 button keyblock for a telephone set as an example, this is not a limitation to the principles involved, which may be used to code uniquely and at maximum economy of light sources and detectors, any matrix array of push-buttons.

Indeed it will be apparent that by adding a fourth column to Figure 1, the three unused codes of TAble 3 are generated, giving a 15button input, and theoretically only 6 detectors are needed to achieve 63 codes. In practice however, the mechanical simplicity of using simpler light guides having only a two-way split as per B column of X row of Figure 1, may be preferable. Even so, the addition of two more detectors to the options discussed above could lead to a further 12 codes being added (27 maximum) and the addition of two more detectors to both the horizontal and vertical coordinates of the matrix would result in a maximum of 48 codes of not more than 4 variables being available. A matrix of 13 columns of 4 rows could readily be coded using only five light sources (or one light source split into 5), and two detectors, resulting in 51 codes.

Opinions vary as to what constitutes a correct and incorrect operating mode for keyblocks. In telephony, the general principle is to accept as a valid code each unique operation of a single button after an allowance of a period of a few milliseconds for contact bounce. Thus the next code is not accepted until all buttons have been restored to the idle condition for a predetermined period, i.e. "finger walking" or "roll over" are not permitted. Using this type of keyblock it requires only very simple timing circuits to ensure that if two keys are operated without an idle condition between the two operations, only the first code to be generated is accepted. Thus although the simultaneous operation of two buttons results in a false code being generated, e.g.

Digits 1 and 3 pressed together give a code equivalent to Digit 2, it will not result in the sending of an incorrect digit. It is, of course, not possible to distinguish the deliberate completely simultaneous pressing of two buttons at once from a genuine code, but this would be exceedingly difficult to achieve, and virtually never occurs accidentally.

If roll-over from one key to the next without passing through the idle state is permitted, it is only possible to use timing circuits to differentiate between a genuine key operation and a false code generated during the roll-over period. By counting strobe pulses, it is very easy to set limits for an acceptable roll-over time but to ensure security of operation, it is better to restrict the permissible coding patterns to odd multiples in either co-ordinate. "Roll-over" may then be imeediately detected as a code having an even number of variables. Figure 3 illustrates a possible keyblock arrangement.

In Fig. 3, there are four columns A, B, C and D and four rows W, X, Y and Z, and for the columns there are three light pipes each serving two columns, and a similar arrangement is provided for the rows. In this arrangement, if the light sources at B and X are strobed the column detectors can be used for row detection.

Many physical realisations of keyblocks according to this invention are possible. The light sources may be light-emitting diodes and those operating in the infra-red portion of the wavelength are particularly suitable.

The detectors will, of course, be chosen to have optimum sensitivity at the corresponding wavelength. The light guides of the matrix could be formed by grooves or tunnels in a moulding or from collapsible tubing. The changes in direction from one guide to another, or for multiplex light sources or detectors, can utilise optical fibres, light guides, or other transparent material utilising the principle of internal reflection, or reflecting surfaces. The light shutters at the intersection points may be achieved either directly by a suitable stem projecting from the push-buttons, or indirectly by collapsing inwards a flexible membrane covering the upper surface of the keyblock.

In Figure 4, the usual 12 buttons arranged in a 4 x 3 matrix used in a telephone keyblock are shown, with the top surface partly cut away. As shown the light pipes have reflectors as indicated, for instance at 10 where they bend. The light pipe under the middle column has a light emitting diode 11, and at the lower end this pipe splits into two pipes 12, 13 one to columns A and one to column C. A similar light source 14 is provided for the rows. In this arrangement it will be noted that the light pipes are so interconnected that two detectors 15 and 16 are used.

The key arrangements are as shown in Figure 5, which is a section along the line X-X of Figure 4. Here we see the pushbutton 17 which acts on a resilient member 18 so that its lower portion can be depressed to cut off light in the light pipe, which is a groove 19 in the push-button frame. The light source 14 is also shown, with a reflector 20 above it. Note that this push button 17 when operated cuts off light in two pipes, and its return to rest is effected by the resilience of the membrane 18, which may be assisted by a spring if necessary.

WHAT WE CLAIM IS: 1. A push-button set which includes a coordinate matrix of push-buttons each of which when depressed causes the generation of a code combination individual to the depressed push-button, which push-button set includes first and second sets of light pipes extending parallel to the rows and columns respectively of said pushbuttons and so arranged that each said push

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. fourth column to Figure 1, the three unused codes of TAble 3 are generated, giving a 15button input, and theoretically only 6 detectors are needed to achieve 63 codes. In practice however, the mechanical simplicity of using simpler light guides having only a two-way split as per B column of X row of Figure 1, may be preferable. Even so, the addition of two more detectors to the options discussed above could lead to a further 12 codes being added (27 maximum) and the addition of two more detectors to both the horizontal and vertical coordinates of the matrix would result in a maximum of 48 codes of not more than 4 variables being available. A matrix of 13 columns of 4 rows could readily be coded using only five light sources (or one light source split into 5), and two detectors, resulting in 51 codes. Opinions vary as to what constitutes a correct and incorrect operating mode for keyblocks. In telephony, the general principle is to accept as a valid code each unique operation of a single button after an allowance of a period of a few milliseconds for contact bounce. Thus the next code is not accepted until all buttons have been restored to the idle condition for a predetermined period, i.e. "finger walking" or "roll over" are not permitted. Using this type of keyblock it requires only very simple timing circuits to ensure that if two keys are operated without an idle condition between the two operations, only the first code to be generated is accepted. Thus although the simultaneous operation of two buttons results in a false code being generated, e.g. Digits 1 and 3 pressed together give a code equivalent to Digit 2, it will not result in the sending of an incorrect digit. It is, of course, not possible to distinguish the deliberate completely simultaneous pressing of two buttons at once from a genuine code, but this would be exceedingly difficult to achieve, and virtually never occurs accidentally. If roll-over from one key to the next without passing through the idle state is permitted, it is only possible to use timing circuits to differentiate between a genuine key operation and a false code generated during the roll-over period. By counting strobe pulses, it is very easy to set limits for an acceptable roll-over time but to ensure security of operation, it is better to restrict the permissible coding patterns to odd multiples in either co-ordinate. "Roll-over" may then be imeediately detected as a code having an even number of variables. Figure 3 illustrates a possible keyblock arrangement. In Fig. 3, there are four columns A, B, C and D and four rows W, X, Y and Z, and for the columns there are three light pipes each serving two columns, and a similar arrangement is provided for the rows. In this arrangement, if the light sources at B and X are strobed the column detectors can be used for row detection. Many physical realisations of keyblocks according to this invention are possible. The light sources may be light-emitting diodes and those operating in the infra-red portion of the wavelength are particularly suitable. The detectors will, of course, be chosen to have optimum sensitivity at the corresponding wavelength. The light guides of the matrix could be formed by grooves or tunnels in a moulding or from collapsible tubing. The changes in direction from one guide to another, or for multiplex light sources or detectors, can utilise optical fibres, light guides, or other transparent material utilising the principle of internal reflection, or reflecting surfaces. The light shutters at the intersection points may be achieved either directly by a suitable stem projecting from the push-buttons, or indirectly by collapsing inwards a flexible membrane covering the upper surface of the keyblock. In Figure 4, the usual 12 buttons arranged in a 4 x 3 matrix used in a telephone keyblock are shown, with the top surface partly cut away. As shown the light pipes have reflectors as indicated, for instance at 10 where they bend. The light pipe under the middle column has a light emitting diode 11, and at the lower end this pipe splits into two pipes 12, 13 one to columns A and one to column C. A similar light source 14 is provided for the rows. In this arrangement it will be noted that the light pipes are so interconnected that two detectors 15 and 16 are used. The key arrangements are as shown in Figure 5, which is a section along the line X-X of Figure 4. Here we see the pushbutton 17 which acts on a resilient member 18 so that its lower portion can be depressed to cut off light in the light pipe, which is a groove 19 in the push-button frame. The light source 14 is also shown, with a reflector 20 above it. Note that this push button 17 when operated cuts off light in two pipes, and its return to rest is effected by the resilience of the membrane 18, which may be assisted by a spring if necessary. WHAT WE CLAIM IS:

1. A push-button set which includes a coordinate matrix of push-buttons each of which when depressed causes the generation of a code combination individual to the depressed push-button, which push-button set includes first and second sets of light pipes extending parallel to the rows and columns respectively of said pushbuttons and so arranged that each said push

button is aligned with two of said pipers, one for that button's row and one for that button's column, wherein each said light pipe is arranged to traverse two of said rows or two of said columns, wherein each said light pipe is served at one of its ends by a light source and at the other of its ends by a light detector, and wherein the depression of one of said push-buttons blocks the passage of light along at least two of said pipers, one of which belongs to the pushbutton's row and one to the push-button's column, so that when a said push-button is depressed the passage of light is blocked in a combination of said pipes individual to the depressed push-button.

2. A push-button set as claimed in claim 1, and wherein the light sources for two of said pipes are combined, using light pipes or reflectors.

3. A Dush-button set as claimed in claim 1, wherein the light which traverses said light pipes is pulsed with the pulsIng occurring alternately in the row and column light pipes so that a suitably connected light detector can function for a row pipe and a column pipe.

4. A push-button set as claimed in claim 1 2 or 3, and wherein each said light pipe is a tube made of a flexible material, the interruption of light transmission therethrough being effected by locally squashing one or more of the tubes on depression of a push-button.

5. A push-button set as claimed in claim 1, 2 or 3, and wherein each said light pipe is a groove or a tunnel in a block of material, each said interruption of a light pipe being effected by the interposition of a movable light shutter into that light pipe when a push-button is depressed.

6. A push-button set as claimed in claim 1, 2, 3, 4 or 5, and wherein each connection between a row pipe or a column pipe is effected by a light guide which permits internal reflection.

7. A push-button set substantially as described with respect to the drawings accompanying the Provisional Specification.