DEVICE FOR CONTROLLING EQUIPMENT

The present invention relates to devices, for use by patients with paralysis and therefore having limited motor function, for controlling peripheral equipment.

Patients having paralysis due to a spinal cord injury which is high up in the neck are left with limited motor function which, in severe cases, may be restricted to the ability to move only their facial muscles. It can be particularly difficult for such patients to gain any independence and have control over equipment and systems within their local environment. Such equipment may include lighting, television, computers or an alert system for calling for assistance.

Conventionally, a patient may be supplied with micro-switches which are placed close to the patients face e.g. adjacent to the surface of their cheek. These micro-switches are activated by pushing the tongue against the inside of the cheek so that the surface of the cheek is brought into contact with the micro- switch thus forcing it to close. There are a number of disadvantages associated with these conventional installations. The location and positioning of the micro- switches are difficult to achieve. The micro-switches are generally mounted on an adjustable support bracket that needs to be rigidly attached to the patient's bed or wheelchair. If the patient's head moves, the switch needs to be repositioned. Furthermore, the conventional switch is sensitive and is, therefore, susceptible to spurious activation when the patient speaks.

It is desirable to provide a means of controlling peripheral equipment which overcomes some of the aforementioned disadvantages.

According to a first aspect, the present invention provides a device for controlling equipment comprising: an electrode arrangement for detecting an electromyogram signal from the user; and a switching arrangement configured to receive the electromyogram signal, the switching arrangement comprising: a precision clamp configured to tie the received signal to a reference voltage; a comparator for comparing an intensity of the signal to a threshold value to determine whether the signal is indicative of a deliberate intent of the user; and an output module for outputting an instructing signal to the equipment based upon an output of the comparator.

By providing a switching arrangement based on an electromyogram (EMG) input signal rather than a physical motion detector, a more robust controlling device can be implemented for the user. By more robust, we mean a controlling device that is less susceptible to spurious activation and therefore requires less intervention and maintenance by a carer of the user. This benefit is achieved because an EMG signal can be generated by a muscle that the wearer can activate in isolation and at will.

By tying the waveform to a reference voltage the amplitude of the trace is exaggerated, in fact it is effectively doubled making variations in the trace much easier to detect and compare to a predetermined threshold. Thus the robustness of the device is further improved. Further, by using a precision clamp rather than a conventional precision rectifier, the frequency spectrum of the clamped signal more closely resembles that of the original EMG signal.

The output module may be one of the group of a relay, a switching transistor and an optoisolator.

The device may comprise means for receiving and modifying the threshold value to adjust the sensitivity of the switching arrangement. The intensity of the signal may be represented by a magnitude or amplitude of the signal.

The switching arrangement may comprise an amplifier for amplifying the received signal; and a signal conditioning stage configured to filter the received signal.

According to a second aspect, the present invention provides a method of controlling equipment comprising the steps of: receiving a signal from a user; substantially continuously clamping the signal to a reference voltage; comparing the intensity of the waveform of the clamped signal to a threshold value to determine whether the signal is indicative of a deliberate intent of the user; and

if the threshold has been exceeded, sending an instructing signal to the equipment.

The method may involve amplifying the signal and filtering the signal prior to the clamping step.

According to a third aspect, the present invention provides a method of controlling equipment by a user having limited motor functionality using the aforementioned device the method comprising the steps of: installing one or more electrodes of the electrode arrangement on the skin of a user adjacent to a muscle that can be deliberately activated in isolation; connecting the electrodes to the switching arrangement; voluntarily causing a contraction of a muscle to send an electromyogram signal to the device, to thereby generate an instructing signal to control the equipment.

The invention will now be described in detail, by way of example only, in reference to the accompanying drawings in which:

Figure 1 illustrates a schematic block diagram of the device; Figure 2 illustrates how the device of Figure 1 may be worn; Figure 3 illustrates an electromyogram (EMG) signal waveform; Figure 4 illustrates conventional rectification of the waveform shown in Figure 3;

Figure 5 illustrates the EMG signal of Figure 3 as processed by the present invention; and

Figure 6 illustrates a precision clamping module.

Whenever a muscle contracts, it produces a small electrical signal that is referred to as an electromyogram (EMG). It is possible to detected EMG signals, generated by the muscle, at the surface of the skin. When the muscle is relaxed only background levels of EMG are present. If the user subsequently, voluntarily, contracts the muscle, the level of EMG increases and the variation thereof can be detected. The EMG signal is used by the present invention to operate a switch.

Figure 1 illustrates a block diagram of the EMG operated switching unit 70 for use by patients with paralysis, to control peripheral equipment. Electrodes 10 are located on the patient's skin to detect EMG generated by muscles adjacent thereto. Any facial muscle may be used to provide the EMG to the switching device, however, a preferred muscle is that used to raise the eyebrow as this muscle can be contracted in isolation from other muscles and is not necessary when speaking. Patients with incomplete paralysis may use non-facial muscles if they are able to produce even small levels of muscle twitching e.g. of limbs or digits. Whilst these movements may be insufficient to activate a conventional micro-switch, the EMG produced by the voluntary twitch would be sufficient to activate the device according to the present invention.

The electrodes 10 are each connected to an amplifier 20 via one or more cables 15, the amplifier 20 being connected, in turn, to a signal conditioning module 30. The signal conditioning module 30 is connected to a clamping

module 40. The clamping module 40 is connected to a comparator 50 which, in turn, is connected to a switching output module 60.

Figure 2 illustrates how the device of Figure 1 may be worn by a patient. The electrodes 10 are mounted on a headband 80 such that they are maintained in close contact with the patient's forehead. In so doing, the electrodes 10 are in an appropriate position to detect EMG signals generated by the eyebrow raising muscles of the patient. The headband 80 is connected to the switching unit 70 via cable 15 to convey the EMG signal from the patient to the amplifier 20 of the switching unit 70. An input cable 90 to a peripheral device (not shown) is connected to the switching unit 70, in particular, to an output of the switching output module 60.

In operation, EMG signals are collected using the skin surface electrodes 10 and are then conveyed through cables 15 to the amplifier 20 of the switching unit 70. This signal is then passed to the conditioning module 30 where it is conditioned by filtering and amplifying.

The conditional signal is then substantially continuously passed to the clamping module 40 where it is tied to a reference voltage using a precision clamp contained there within.

The functionality of the precision clamp of the clamping module 40 is illustrated with reference to Figures 3 to 5. Figure 3 illustrates an example waveform that may be output from the conditioning module 30. Figure 4 illustrates a conventional approach to processing such signals, namely, the signal is

rectified so that the negative part of the waveform is converted to become part of the positive part of the waveform at the same amplitude. Figure 5 illustrates how the precision clamp ties the lowest part of each oscillation (or the wave form "troughs") to a predetermined reference voltage so that all parts of the wave form are then located above this reference voltage. The amplitude of the peaks of the waveform are effectively doubled and the gradient or rate of change of the wave form, and therefore the slew rate, is increased. This exaggeration of the waveform means that it becomes easier and more reliable to detect changes than in the original signal. Consequently, it becomes easier to ascertain when the waveform rises above a particular threshold level even if the amplitude of the original EMG signals are quite small. Indeed, all of the essential component characteristics and shape of the original signal wave form are substantially preserved.

The reference voltage can be any voltage level that is convenient for the application, e.g. ground.

An example circuit diagram representing the precision clamping module 40 is illustrated in Figure 6.

The comparison step, performed by the comparator 50, ascertains whether the signal rises above a particular threshold level. The comparator 50 comprises means for defining a particular threshold level in order to modify the sensitivity of the switching unit.

If the comparator 50 ascertains that the threshold has been exceeded a signal is sent to the switching output module 60 causing actuation thereof and a switching signal is output from the switching unit 70 along cable 90 to the peripheral device (not shown) for initiation of operation thereof.

The device may further comprise a protection circuit (not shown) between the electrodes 10 and the amplifier 20. The protection circuit comprises conventional circuit protection clamping, implemented by e.g. one or more passive diodes and is configured to clamp the circuit to a safe maximum and/or minimum voltage should a potentially damaging voltage be encountered.

The precision clamp provides a form of signal rectification that substantially preserves the signal characteristics and enables easy matching to follow on circuitry.