WO2002045621A2

WO2002045621A2 - Upper extremity prothesis actuated by a sensor using near-infrared spectroscopy

Info

Publication number: WO2002045621A2
Application number: PCT/IT2001/000606
Authority: WO
Inventors: Gennaro Verni; Daniela Zambarbieri
Original assignee: Inail-Centro Per La Sperimentazione Ed Applicazione Di Protesi E Presidi Ortopedici Per Gli Infortuni Sul Lavoro
Priority date: 2000-12-04
Filing date: 2001-11-30
Publication date: 2002-06-13
Also published as: AU2002222548A1; ITMC20000099A1; IT1316110B1; WO2002045621A3

Abstract

The present invention relates to an upper extremity prosthesis characterised by the fact the housing contains two optical sensors (1a, 1b) that use near-infrared spectroscopy to detect the contraction and relaxation of the agonist and antagonist muscles of the stump and translate them in actuation commands for the motorised artificial hand of the prosthesis by means of suitable management electronics.

Description

Upper extremity prosthesis actuated by a sensor using near-infrared spectroscopy.

The present patent application relates to an upper extremity prosthesis actuated by sensors using near-infrared spectroscopy theory.

As it is known, upper extremity myoelectrical prostheses have been available for a long time. These prostheses are actuated by means of surface electromyography, that is using electrical potentials detected on the cutis at the level of the muscles of the stump to which the prosthesis is applied, when these muscles contract.

More precisely, the signals generated by the muscles are detected by special electrodes situated in the prosthesis housing in direct contact with the patient's cutis.

These prostheses can be actuated in two different modes: with an ON/OFF system and with a multi-channel system.

The ON/OFF system allows to control only one movement at a time by contracting a single muscle. On the contrary, with the multi-channel system, the signal generated by the patient's muscles can control various prosthesis movements, based on the signal width.

In this type of prostheses the most typical example is the myoelectrical hand, that is a hand with an electrically controlled micromotor based on the potential detected on the cutis of the stump to which the prosthesis is applied. This potential has an efficacious value when it ranges from a few decimals of mV to 2mV. Such a signal becomes suitable for controlling the micromotor following to 10⁴ amplification, reaching 0-3.5 V dynamics.

In practice, the micromotor is actuated by a power circuit with H-bridge structure, with 5 pins in the upper part and 2 pins in the lateral part. The electrical diagram of the circuit comprises two integrated circuits that represent the real actuator of the micromotor.

As regards the input stage, two diodes 1N4148 create a threshold that, when exceeded, activates the corresponding input (EMG1 or EMG2).

Compatibly with the activated muscle, an electromyographic signal will reach one of the two inputs (EMG1 or EMG2) and the motor will open or close the hand. It must be noted that the power circuit in charge of actuating the hand is associated with a mechanic switch that can be controlled from the wrist and used by the patient to deactivate the prosthesis.

Although this is the most popular technology used for the actuation of prostheses, it must be said that it presents considerable drawbacks, due to: • Electromagnetic interference in the air

• Cross-talk due to the activation of other muscles located near the muscles on which the prosthesis is applied

• High pressure of the electrodes needed against the patient's cutis in order to detect the electrical signal • Poor quality of the electrical signal in case of patients with traumatic amputation, with consequent reduction of muscular contractility. The prosthesis according to the present invention was devised in view of the aforementioned inconveniences and uses a different technology, namely the near-infrared (NIR) spectroscopy. As regards the study of muscular tissues, near-infrared spectroscopy uses the difference between the absorption spectrum of free and oxygenated haemoglobin. The two forms of haemoglobin have exactly the same absorption spectrum at 800 nm (isosbestic point). Therefore, the light absorption at this wavelength is proportional to the total contents of haemoglobin in the concerned tissue.

In view of the above, a new use of the aforementioned technology was devised, based on the evaluation of the intensity and duration of individual muscular contractions of the stump to which the prosthesis is applied. For major clarity the description of the invention continues with reference to the enclosed drawings, which are intended for purposes of illustration and not in a limiting sense, whereby: - fig. 1 is a chart that illustrates the functional properties of the technology according to the present invention compared with traditional technology;

- fig. 2 is an axonometric view of one of the sensors used in the prosthesis according to the present invention;

- fig. 3 shows the electronic circuit used to manage the prosthesis; - fig. 4 is an schematic axonometric representation of a possible embodiment of the prosthesis according to the present invention, designed for a patient whose arm was amputated under the axilla.

A scattered signal is used to evaluate the intensity and duration of individual muscular contractions. The signal is obtained from a wavelength beyond the isosbestic point and gives information on the total contents of haemoglobin and therefore on the total quantity of blood that circulates in the concerned area.

Preliminary studies were carried out to detect the muscular contraction by simultaneously using a standard EMG electrode for myoelectrical prostheses and a reflectance oximeter (TIREOX, Laros S.a.s., Pavia) using 810 nm wavelength.

Fig. 1 shows an example of the two signals recorded during a short muscular contraction. The figure shows the perfect similarity of the morphology of the two signals. The prosthesis according to the present invention was devised starting from the experimental results and in consideration of some important technical factors. More precisely, the new sensor used to actuate the prosthesis was devised.

Special attention was paid to reduce the sensor dimensions since it must be contained inside the housing of the prosthesis that contains the cutaneous electrode in the standard version of the INAIL Prostheses Centre.

With reference to figure 2, the sensor (1) uses a special emitter (2) composed of a LED OD 870 F (4.5 mW power) that emits a 50 nm band centred on 870 nm wavelength. A LED is used because it is easy to control and not very sensitive to thermal fluctuations, and also because it can support the light source directly, allowing for placing it in contact with the cutis. The sensor (1) uses an integrated photodetector OP 211 (3) to detect the signal reflected by the stump muscle.

The distance between emitter and receiver, from which the maximum depth of photon penetration depends, is 12 mm. In order to avoid damaging the electrical components of the sensor, the surface of the sensor is covered with waterproofing, biocompatible and hypoallergenic optical glue. The operation of the prosthesis according to the present invention is ensured by a pair of optical sensors (1), one for the agonist muscle and one for the antagonist muscle. The pair of sensors is controlled by means of the electronic circuit shown in figure 3.

In the first sensor the main clock is supplied by an integrated circuit LM555 that provides a square wave at 1 kHz. The impulses are formed through two integrated circuits 74HC123 to have a duration of 0.1 ms and then sent to a driver LED capable of supplying up to 60 mA to the LED (i.e. integrated circuit 74F3037). The luminous radiation diffused by the muscular tissues is received by an amplified photo diode OP 211 with transimpedance gain equal to 1 Mohm.

The pre-amplified signal is injected in a "sample and hold" controlled by the pair of integrated circuits 74HC123 that form it and are suitably delayed starting from the square wave in order to be in phase.

The signal is sent to a voltage amplifier with selectable gain through a dip- switch. It is an operational amplifier LF347 in non-inverting configuration. The second sensor is the same as the first sensor described above, with the only difference that the luminous impulses of the first sensor have a displaced phase with respect to the luminous impulses of the second sensor, in order to avoid interference on tissues. It uses the same main clock given by the integrated circuit LM555, while the integrated circuits 74HC123 produce a delay compared to the first sensor. Finally, it must be noted that the pair of optical sensors was connected to the power driver of the hand prosthesis using a PC with suitable acquisition board, in order to ensure valid operation. The signal from the two sensors is digitised and amplified in order to be compatible with the input levels foreseen by the power driver.

In practice, the two optical sensors (1a, 1 b) used in the prosthesis according to the present invention are placed on the patient's stump in the same positions as the EMG electrodes of traditional prostheses and the patient must make the same muscular contractions that are required for traditional prostheses.

Suitable experiments showed that the signals taken by the optical sensors of the new prosthesis according to the present invention can open and close the hand prosthesis perfectly. ' Finally, figure 4 shows the practical application of the sensors (1a, 1b) to the aforementioned embodiment of the upper extremity prosthesis according to the present invention.

The prosthesis (100) has a traditional housing (100a) that contains the stump. The housing (100a) contains the two sensors (1a, 1b) so that the first sensor takes the signal produced by the agonist muscle and the second sensor takes the signal produced by the antagonist muscle of the stump.

The housing (100a) used in the model of prosthesis illustrated in figure 4 is hinged by means of a motorised elbow (101) to the prosthetic forearm (102) with a motorised prosthetic hand (103). Apart from the amplifier and the power circuit, the prosthetic forearm (102) contains the power supply units (104) that provide power for the operation of the prosthesis (100).

In spite of the fact that figure 4 illustrates a model of designed for patients whose arm was amputated right under the axilla, it is understood that the idea of the present invention can be advantageously applied to different versions of upper extremity prostheses, that is in the case of patients whose arm was amputated at different levels, including the wrist level.

This is possible because the prostheses are always provided with the housing that, according to the present invention, contains the two sensors (1a, 1b) using near-infrared spectroscopy for their operation.

Claims

1) Upper extremity prosthesis, of the type that comprises a housing (100a) for the stump and ends with a motorised prosthetic hand (103), characterised by the fact that the housing (100a) contains two optical sensors (1a, 1b), the first one for the agonist muscle and the second one for the antagonist muscle, that use near-infrared spectroscopy to detect the contraction and relaxation of the agonist muscle of the stump and the contraction and relaxation of the antagonist muscle of the stump, respectively; it being provided that the contraction and relaxation of the muscles detected by the sensors (1a, 1 b) are translated into actuation commands for the motorised prosthetic hand (103) by means of a suitable management electronic circuit.

2) Upper extremity prosthesis, according to the previous claim, characterised by the fact that each optical sensor (1a and 1 b) uses:

- an emitter (2) composed of a LED OD 870 F (4.5 mW power) that emits a 50 nm band centred on 870 nm wavelength - an integrated photodetector OP 211 (3) used to detect the signal reflected by the stump muscle it being provided that the distance between emitter and receiver is 12 mm.

3) Upper extremity prosthesis, according to the previous claims, characterised by the fact that the in the first of the sensors (1a and 1 b) the main clock is supplied by an integrated circuit LM555 that gives a square wave at 1 kHz.

4) Upper extremity prosthesis, according to the previous claims, characterised by the fact that the impulses supplied by the integrated circuit LM555 are first formed by means of two integrated circuits 74HC123 to have a duration of 0.1 ms and then sent to a driver LED capable of supplying up to 60 mA to the LED (integrated circuit 74F3037); it being provided that:

- the luminous radiation diffused by the muscular tissues is received by an amplified photodiode OP 211 with transimpedance gain equal to 1 Mohm.

- the pre-amplified signal is injected in a "sample and hold" controlled by the pair of integrated circuits 74HC123 that form it and are suitably delayed starting from the square wave in order to be in phase

- and the signal is sent to a voltage amplifier with selectable gain through a dip-switch, consisting in an operational amplifier LF347 in non-inverting configuration. 5) Upper extremity prosthesis, according to claims 3 and 4, characterised by the fact that the second of the sensors (1a and 1b) is the same as the first sensor, with the only difference that the luminous impulses of the first sensor are displaced in phase with respect to the luminous impulses of the second sensor, so that the same main clock of the integrated circuit LM555 is used, while the integrated circuits 74HC123 produce a delay compared to the first sensor.

6) Upper extremity prosthesis, according to the previous claims, characterised by the fact that the pair of optical sensors (1a and 1b) is connected to the power driver of the prosthetic hand by means of a PC with suitable acquisition board, in order to ensure valid operation; it being provided that the signal from the two sensors is digitised and amplified in order to be compatible with the input levels foreseen by the power driver.

7) Upper extremity prosthesis, according to claim 2, characterised by the fact that the surface of the electrical components of the sensors (1a and 1 b) is covered with waterproofing, biocompatible hypoallergenic optical glue.

8) Upper extremity prosthesis, according to claim 1 , characterised by the fact that its operation is managed through the electronic circuit illustrated in fig. 3 .