GB2034043A

GB2034043A - Improvements in or Relating to Controls for Electrical Circuits

Info

Publication number: GB2034043A
Application number: GB7839760A
Authority: GB
Original assignee: TURNRIGHT CONTROLS
Current assignee: TURNRIGHT CONTROLS
Priority date: 1978-10-09
Filing date: 1978-10-09
Publication date: 1980-05-29

Abstract

A touch pad comprising a plurality of touch pads 0, 1, 2 ...9, P, F located upon the upper surface of a dielectric material, and on the lower surface an energising electrode common to all the touch pads and a series of pick-up electrodes. Each touch pad is capacitively coupled to a unique combination of two of the pick-up electrodes so that contact with a touch pad produces a change in output from the unique combination to which the touch pad is coupled. Several of the touch pads 10 ... 13 may be used in conjunction with a microprocessor to control the heating rings or plates of an electric cooker. The microprocessor is programmed to respond only to contact with a touch pad of a duration greater than a predetermined value and less than another different predetermined value. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Controls for Electrical Circuits This invention relates to controls for electric circuits and has particular reference to controls for the electric circuits used in domestic equipment for example electric cookers, washing machines, food mixers.

Many items of electric equipment incorporate control switches which project above the otherwise smooth surface of the equipment. It has been suggested that the so-called touch switches be used in such circumstances.

However, the use of such switches gives rise to other problems. The switches are sensitive and can easily be actuated accidentally. Thus, if used to control the hot plates or rings of an electric cooker or an electric hob, accidental actuation of a switch and the subsequent energisation of the hot plate or ring creates a considerable hazard.

It has been suggested thaahat the risk may be reduced by the incorporation of an additional switch with a built-in time delay. Such a switch may control the connection to a source of mains supply and if the associated switch is not actuated with the period of the time delay the additional switch reverts to its "off" position, power being disconnected.

In the case of many items of equipment a "power-on" switch such as the additional switch just described is used together with a plurality of other switches each used to seiect a different condition, for example, heat output of a hot plate or ring, the motor speed of an electric food mixer, or a required program of a washing machine or dish washer.

A number of different methods of effecting the selection have been proposed. One method utilizes a count-up/count-down method but this takes time. Another method utilizes a number of separate touch switches but this requires space.

According to the present invention a keyboard control panel comprises a plurality of touch pads, and, associated with the pads, a plurality of pickup electrodes and of energising electrodes, the arrangement being such that each of at least some of the touch pads is capacitively coupled to a unique combination of at least two of the pickup electrodes whereby bodily contact with any one of the said some touch pads produces a change in output from each of the pick-up electrodes to which the touch pad is coupled.

Conveniently, each of the said some touch pads is capacitively coupled to a unique combination of two pick-up electrodes. It is found, in practice, that problems with signal levels arise if the number of electrodes in each unique combination exceeds four and even in the case of four electrodes, signal stabilisation may be required.

When incorporated in a control system for an electric appliance, the keyboard just described may input to a microprocessor programmed to de-energise the appliance if contact with a touch pad is maintained for a period of time greater than a predetermined value.

In addition, the microprocessor may be programmed to respond only to contact with a touch pad of greater than a predetermined time duration.

In an alternative form the invention includes a control system for an appliance, comprising a keyboard with a plurality of touch switches, and a microprocessor to which the keyboard inputs, the microprocessor being programmed to de-energise the appliance if contact with a touch switch is maintained for a period of time greater than predetermined period of time. In addition, the microprocessor may be programmed to respond only to contact with a touch switch of greater than a predetermined time duration.

In one particular keyboard control panel, an energising electrode is used that is common to at least some of the pick-up electrodes. In one embodiment, the energising electrode is common to all the pick-up electrodes.

In one form of keyboard control panel, the energising electrode has a central area from which extend a number of radial arms thereby forming a plurality of "pockets" in which pick-up electrodes are located. In this form, touch pads are so located that some of the pads inductively couple the energising electrode to a unique combination of several of the pick-up electrodes-for example two pickup electrodes.

The pick-up electrodes and touch pads may lie on a circle in which case a display unit, for example a seven segment display unit may be located within the circle. The display can be used to indicate visually which of the touch pads has been touched by a user.

Alternatively, the arrangement of the touch pads and pick-up electrodes and in some cases the energising electrode or electrodes may be of linear form or of curvilinear form other than circular.

By way of example only, embodiments of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figs. 1 and 2 are, respectively, the upper and lower surfaces of a control embodying the invention, Fig. 3 is a circuit showing, mainly in block schematic form, an electric hob incorporating a control embodying the invention, and, Fig. 4 is an explanatory algorithm.

The control shown in Figs. 1 and 2 is a touch keyboard intended principally for incorporation in a ceramic electric hob unit and it comprises twelve touch pads designed 0, 1...9, P, F located upon the upper surface 1 of a layer of dielectric material in this case the glass layer of the hob.

The figures denote increasing increments of rate of heat input commencing with "0" indicating "OFF" whilst "P" and "F" denote, respectively, controlled heat inputs used for heating, for example, milk or sauces where a controlled relatively low temperature is required, and, for frying for example where a higher controlled temperature is required. Control is effected by means of a thermostat as will be described later.

The pads are arranged in a circle round a display unit of the 7-segment display type adapted to display a digit or letter representing that one of the pads that has been selected or touched.

On the undersurface of the layer 1 are arranged the energising and pick-up electrodes 3, 4 of the touch pads. The electrodes are shown in fuil lines in Fig. 2, and in dotted lines in Fig. 1 so that their positions relatively to the pads is clear.

A single energising electrode 3 is used whose configuration has separate "pockets" 4 in which the pick-up electrodes 5 are located. As can be seen from Fig. 1, each aiternate pad bridges adjacent pick-up electrodes to an extent sufficient to ensure that touching the pad produces outputs on both of the adjacent electrodes bridged by the pad. The remaining pads are located centrally or substantially so of the respective pick-up electrodes and touching any one of these pads produces an output from the associated single electrode only.

In this way, the area occupied by the keyboard is considerably reduced because a more compact arrangement of the electrodes is possible. The resultant saving in space makes a more attractive layout possible.

The keyboard just described may, of course, take forms other than that shown in Figs. 1 and 2.

The arrangement of the pads, energising and pick up electrodes could be linear, or of curvilinear form other than circular. In addition, some of the touch pads may be associated with three or more electrodes.

In addition, the display need not be located centrally of the keyboard as explained above but could be at some other location, for example, to one side or the other of the keyboard.

The keyboard described above is used with a microprocessor programmed to accept an input from a single electrode of the keyboard or a simultaneous input from two electrodes but no more. Thus, the system is of a "threekey" lock out.

Fig. 3 shows a circuit in block schematic form of an electric hob with four rings or plates 6, 7, 8, 9 each with its own controlling keyboard 10, 11, 12 and 1 3 respectively. The keyboards operate through a microprocessor shown as box 14, and typically of Type F3870, to control the conducting cycle of triacs 1 5, 16, 17, 18 associated respectively with the rings 6... 9 to control the supply of electricity thereto.

The input to the microprocessor includes an input from an "enable" touch switch 1 9 common to all the keyboards and which must be operated before power can be applied to any ring. Once operated, and latched, for one ring, switch 1 9 does not need to be operated for another ring.

Switch 1 9, through the intermediacy of the microprocessor, controls the energisation and deenergisation of the winding 20 of an electromagnetic switch 21 in the mains supply to the rings 6... 9 via the respective triacs 15... 18.

The microprocessor also controls the energisation of the display units of the keyboards when a pad is touched, the display shows a symbol indicating that pad.

Rings 6 and 7 have associated with them thermostats that control the heat output of the ring at a preselected value. The thermostats have thermal sensors 22, 23 which input to the microprocessor as shown.

In the "inactive" condition of the circuit, the electromagnetic switch 21 is de-energised so that the rings 6... 9 cannot be energised. Additionally, the microprocessor, energised via its own power supply, inhibits any form of output to the triacs 15... 1 8 and the 7-segment indicators associated with the keyboards 10... 1 3 are blanked off.

If, now a user wishes to bring one or other of the rings 6... 9 into use, the "enable" switch 1 9 is first operated. This energises the winding 20 of the electromagnetic switch 21 which closes, and also causes the microprocessor to energise the indicators of all the keyboards to display the digit "O". The user must now select a particular ring to be energised and if this is not done within a predetermined time, for example 5 seconds, the entire unit is returned to the "inactive" position as described above.

Having decided which ring is required, the user then merely touches the pad area of the associated keyboard designating the heat required, e.g. for a very low heat, pad 1 would be touched, or for maximum heat, pad 9 would be touched. The microprocessor is programmed to respond only to contact of a duration greater than a predetermined time, for example 100 m sec. but less than a greater time for example 3 sec.

Assuming that contact is maintained for a period of time within that range, the keyboard then signals to the microprocessor the identity of the pad that has been touched and the microprocessor operates the triac of the selected ring by sending firing control pulses of fixed duration at those instants of time in the mains supply cycle when the supply voltage is zero.

Control over the input of heat to the selected ring is effected by burst firing of the triac over a period of for example 1 5 seconds. In addition, the microprocessor stimulates the indicator of the particular keyboard to display that digit or letter showing the heat value that has been selected and also holds the switch 21 in its closed condition.

The microprocessor is programmed to respond only to predetermined inputs from the keyboards.

Thus, the microprocessor will respond to valid inputs only and ignore all other inputs. For example, if a user inadvertently touches two pads simultaneously there will be no response from the microprocessor. On the other hand, if a user, intending to touch one pad, inadvertently touches another, the error can be corrected by touching the required pad after a period of time greater than 100 m secs. If the period of time is less than 100 m sec, the microprocessor will respond to the pad first touched by the user.

Furthermore, if a user, whilst maintaining contact with one pad, touches another, the microprocessor will not respond to contact with the second pad except for valid combinations until the user releases contact with the first pad and maintains contact with the second for a period of time greater than 100 m sec and less than 3 secs.

If another ring is to be brought into use, the user simply touches the appropriate touch pad of the keyboard controlling the other ring and this brings the ring into operation in a manner similar to that already described above with reference to the first ring. The microprocessor is programmed to ensure that the burst firing of the two triacs, associated with the rings now in use, is staggered in time to minimise the maximum simultaneous electrical load.

Further rings are brought into use in the same way and the burst firing of each additional ring is time staggered with that of rings already in use.

When the user has finished with a particular ring, the "0" touch pad of the appropriate keyboard is touched. This action results in the microprocessor ceasing to operate the triac of the particular ring which is thus de-energised and the seven-segment display shows "0".

When all rings have been taken out of use, the system will automatically return to the "inactive" condition as explained above after the 5 second time delay referred to above.

If a touch pad of any keyboard is touched, either deliberately or accidentally, for a period of time greater than a predetermined maximum for example 3 seconds, the microprocessor automatically inhibits the triac of the ring associated with the keyboard and causes the seven-segment display thereof to show "0". This prevents, the accidential energisation of a ring by, for example, a cooking utensil or some other article inadvertently left on a touch pad.

The minimum contact time of 100 m sec prrevents very brief intermittent contact with pads from registering a valid input to the microprocessor. In addition, it prevents voltage disturbances of brief duration from giving rise to false responses.

Associated with hob described above may be a timer with, for example, a two-digit display indicating tens of minutes and minutes. This can be used to time cooking operations and is settable by means of a keyboard with two touch pads one marked "+" and the other marked "-". These touch pads input to the microprocessor which has an output controlling the two seven-segment displays of the timer.

In the "inactive" condition the timer is deenergised and its display is blank and until switch 19 is touched, the display remains blank.

A short push on the "+" pad will turn the timer on and the display will show "1". For every short contact with the "+" pad the setting will increment once.

If contact with the "+" pad is maintained the setting will start incrementing after a short time delay.

Similarly, when the timer is de-energised, a short push on the "-" pad will turn the timer on and the display will show "99". For every short push of the "-" pad the setting decrements once.

If contact with the "-" pad is maintained, the timer turns off after a small time delay.

It is also preferable that the time should be decremented automatically during a timed operation so that it indicates the time remaining before the expiry of a timed period. In addition, on the expiry of the timed period, the timer should emit a visible and/or audible warning which is terminated by a user contacting one of the timer pads, for example the "-" pad. It may also be desirable that for periods of time less than 10 minutes, the timer should indicate the units value only and the tens value of "O" be blanked-off and not displayed, that is to say, the leading zero is suppressed.

Reference has been made above to the fact that rings 6 and 7 have thermostats that control the heat output of the ring at a preselected value.

The thermostats operate through the microprocessor to control the firing of the associated triacs to maintain the heat output.

When a user wishes to reduce the heat input to a particular ring, the appropriate pad of the keyboard of that ring is touched. The microprocessor is however, programmed to ensure that there is a time delay before the ring is re-energised at the lower value. That delay allows the heat corresponding to the previous, higher setting to be dissipated. After the time delay, the ring is re-energised at the value appropriate to the lower setting.

Similarly, if the ring is at a lower heat output, the microprocessor operates the triac so that the ring is energised at its maximum rate until the requisite higher setting of the ring is reached and then reverts to an operation of the triac appropriate to the higher setting.

The times in question are controlled by taking into account the thermal masses involved, the length of time at the previous setting and the difference between the heat setting.

The microprocessor is so programmed to incorporate a number of safety features. It has already been explained that the system will automatically revert to the "inactive" condition in certain circumstances after a predetermined delay. The delay may be about 5 secs. In addition, the microprocessor is programmed to ignore a signal from a touch pad unless the signal is of at least a predetermined duration suggesting an intentional contact with the touch pad. The duration may be about 100 m sec this being sufficient to prevent response of the microprocessor to any voltage transients that occur. In addition, contact with a touch pad held for a period of time greater than a predetermined time of 3 seconds will cause the microprocessor to de-energise the appropriate ring. Such a safety measure is mentioned above.

The microprocessor may also be programmed to ignore simultaneous operation of the "+" and "-"touch pads of the timer. Preferably, a timing operation commences when a touch pad is released.

Claims

1. A keyboard control panel comprising a plurality of touch pads, and, associated with the pads, a plurality of pick-up electrodes and at least one energising electrode, the arrangement being such that each of at least some of the touch pads is capacitively coupled to a unique combination of at least two pick-up electrodes whereby bodily contact with any one of the said some touch pads produces a change in output from each of the pick-up electrodes to which the touch pad is coupled.

2. A panel as claimed in claim 1, in which each of said some touch pads is so positioned that it bridges the or one of the energising electrodes and the electrodes of the unique combination of pick-up electrodes to which it is capacitively coupled.

3. A panel as claimed in claim 1 or 2, in which each of the said some touch pads is coupled to a unique combination of two pick-up electrodes.

4. A panel as claimed in claim 1, 2 or 3 in which there is a single energising electrode common to some at least of the touch pads.

5. A panel as claimed in claim 4 in which the single electrode has a central area from which extend a number of arms, at least the extremeties of the arms being separated by areas in which the pick-up electrodes are located.

6. A panel as claimed in claim 5 in which some of the touch pads are wholly located within the area of a pick-up electrode and in which each of the some touch pads is located partly within the area of one pick-up electrode and partly within the area of another pickup electrode.

7. A panel as claimed in claim 5 or 6 in which the touch pads lie on the circumference of a circle and in which there is a display unit located at the centre of the circle for displaying visually the identity of an operated touch pad.

8. A control system for an appliance, the system comprising a keyboard with a plurality of touch pads for controlling the operation of the appliance, and a microprocessor to which the keyboard inputs, the microprocessor being programmed to inhibit the energisation of the appliance in the event that contact with a touch pad is maintained for a period of time greater than a predetermined value.

9. A control system as claimed in claim 8 in which the microprocessor is additionally programmed to respond to contact with a touch pad only if the contact is maintained for a period of time less than said predetermined value but greater than a different predetermined value.

10. A control system as claimed in claim 8 or 9 and further comprising an "enable" touch pad so connected that it must be actuated before the system will respond to contact with a touch pad of the keyboard.

1 A control system as claimed in claim 10 and further comprising additional keyboards each comprising a plurality of touch pads, and in which actuation of the "enable" pad prepares the system to respond to contact with a pad on any keyboard and to respond to the subsequent contact with the pad of another keyboard.

12. A control system as claimed in claim 11 in which the microprocessor is programmed to deactivate the system following the termination of the response of the system to each contacted touch pad.

13. A control system as claimed in any one of claims 8-12 in which at least one of the keyboards is a keyboard control panel as claimed in any one of claims 1-7.

14. An electric appliance having a plurality of heating rings or plates and a number of keyboards each having a plurality of touch pads, each keyboard being operatively associated with a different one of the rings or plates, the keyboards inputting to a microprocessor that controls the energisation of the rings or plates in accordance with the contact of the touch pads of the keyboards, and in which the microprocessor is programmed to inhibit the energisation of a ring or plate if in the event that contact is maintained with a touch pad of the keyboard associated with the ring or plate for a period of time greater than a predetermined value.

1 5. An electric appliance as claimed in claim 14 in which the microprocessor is programmed to respond to the contact of a touch pad only if the contact is maintained for a period of time less than said predetermined time but greater than a different predetermined value.

1 6. An electric appliance as claimed in claim 1 5 and further comprising an "enable" touch pad so connected that it must be contacted before a ring or plate will be energised.

17. An electric appliance as claimed in claim 1 6 in which the "enable" switch, once contacted permits energisation of other selected rings or plates and continues to do so until every ring or plate has been returned to a state of deenergisation by contacting the appropriate touch pad, and in which thereafter the "enable" pad must be contacted before a ring or plate will be energised.

1 8. An electric appliance as claimed in claim 16 or 17 in which failure to contact a touch pad of a keyboard within a selected time starting with contact of the "enable" pad results in deactivation of the appliance.

19. An electric appliance as claimed in any one of claims 1 1 7 in which each keyboard is a keyboard control panel as claimed in any one of claims 1-7.

20. An electric appliance as claimed in any one of claims 14-1 7 in which each keyboard is a keyboard control panel as claimed in claim 7 and in which the microprocessor is programmed to energise the display unit to indicate the identity of a selected contacted touch switch of the control panel.

21. A keyboard control panel substantially as described herein with reference to and as illustrated by Figs. 1 and 2 of the accompanying drawings.

22. An electric appliance substantially as herein described with reference to and as illustrated by Figs. 3 and 4 of the accompanying drawings.