ITMC20000099A1 - UPPER LIMB PROSTHESIS OPERATED THROUGH A SENSOR THAT USES SPECTROSCOPY IN THE NEAR INFRARED - Google Patents

Description

DESCRIPTION

accompanying a patent application for an industrial invention entitled:

"UPPER LIMB PROSTHESIS ACTIVATED BY A SENSOR THAT USES THE NEAR INFRARED SPECTROSCOPY".

TEXT OF THE DESCRIPTION

The present patent application for industrial invention relates to an upper limb prosthesis operated by sensors that use the theory of near infrared spectroscopy.

As is known, myoelectric upper limb prostheses have already existed for some time; the actuation of these prostheses is determined by means of surface electromyography, ie using electrical potentials detected on the skin at the level of the muscles of the stump to which the prosthesis is applied, when they are involved in the contraction.

More precisely, the signals generated by the aforementioned muscles are detected by particular electrodes located in the socket of the prosthesis in direct contact with the patient's skin.

The operating modes of such a prosthesis can be of two types: on the basis of an ON / OFF system and on the basis of a multichannel system.

The ON / OFF system allows you to control only one movement at a time with the contraction of a single muscle; while, with the multichannel system, the signal generated by the patient's musculature can command different movements of the prosthesis, based on the amplitude of the signal itself.

In these types of prostheses the component of choice is certainly the myoelectric hand, that is, a hand equipped with a micromotor electrically controlled precisely on the basis of the potential detected in correspondence with the skin of the abutment to which the prosthesis itself is applied.

This potential has an effective value when it varies from a few tenths of a mV to 2mV; such a signal is made suitable for controlling the aforementioned micromotor following an amplification of a factor IO4, capable of making it reach a dynamic of 0-3.5 V.

In practice, the aforementioned micromotor is operated by a power circuit with an H-bridge structure, with 5 pins at the top and 2 pins at the side; the electrical diagram of this circuit comprises two integrated which constitute the real actuator of the aforementioned micromotor.

As regards the input stage, on the other hand, there are two 1N4148 diodes that create a threshold which, once exceeded, activates the relative input (EMG1 or EMG2).

Compatibly with the activated muscle, an electromyographic signal will reach one or the other of the two said inputs (EMG1 or EMG2) and the motor will command the opening or closing of the hand.

It should also be said that this same power circuit responsible for activating the hand is associated with a mechanical switch, operated by the wrist of the hand, designed to allow the patient to disable the prosthesis.

Well, despite the fact that this technology is the most widespread for operating limb prostheses, one cannot help but notice some practical drawbacks of considerable magnitude, due to • electromagnetic interference present in the ether

• cross-talk phenomenon due to the activation of muscles close to those on which the prosthesis is applied

• high force with which the electrodes must be pressed against the patient's skin in order to detect the aforementioned electrical signal

• poor quality of the same electrical signal in those patients who have suffered a particularly traumatic amputation, resulting in a reduction in muscle contractility.

Precisely on the basis of the observation of these drawbacks, the prosthesis according to the invention was conceived, the operation of which is inspired by a completely different technology, in particular that relating to near infrared (NIR) spectroscopy.

In fact, the current use of near infrared spectroscopy in the clinical field exploits, as regards the investigation of muscle tissues, the difference between the absorption spectrum of free and oxygenated hemoglobin. At 800 nm (isosbestic point) the two forms of hemoglobin have exactly the same absorption spectrum; therefore the absorption of light at this wavelength is proportional to the total hemoglobin content in the investigated tissue.

Based on this knowledge, a new use of the aforementioned technology was hypothesized, based on the assessment of the intensity and duration of the individual muscle contractions of the usual stump to which the prosthesis is applied.

For greater explanatory clarity, the description of the invention continues with reference to the attached drawing tables, having only illustrative and certainly not limiting value, in which:

Figure 1 is a graph which serves to illustrate the functional properties of the technology according to the invention in relation to those of the pre-existing traditional technology;

Figure 2 is an axonometric representation of one of the sensors adopted in the prosthesis according to the invention;

- Figure 3 is the electronic circuit for the management of the same upper limb prosthesis;

- Figure 4 is a schematic axonometric representation of a possible embodiment of the limb prosthesis according to the invention, intended in particular for a person who has undergone the amputation of the arm below the armpit.

Well, for the purpose of evaluating the intensity and duration of individual muscle contractions, a scattered signal is informative which, obtained starting from a wavelength beyond the isosbestic point, provides information on the overall hemoglobin content and therefore on the overall quantity of blood flowing through the area under investigation.

Preliminary studies were therefore conducted for the detection of muscle contraction simultaneously using a common EMG electrode for myoelectric prostheses and a reflectance oximeter (TIREOX, Laros S.a.s., Pavia) which uses a wavelength of 810 nm.

The aforementioned figure 1 shows an example of the two signals recorded during the single short-term muscle contraction; in this figure it is possible to see how the morphology of the two signals is perfectly comparable.

Well, starting from these latest experimental results and taking into account some important technical factors, we proceeded to design the limb prosthesis according to the invention and, more precisely, the new sensor responsible for its activation.

Particular attention was also paid to the containment of the dimensions of this sensor, since it is intended to be housed inside the same socket present on the limb prostheses in order to contain the skin electrode in the standard version of the INAIL Prosthesis Center. .

With particular reference to Figure 2, the aforementioned sensor (1) uses a particular emitter (2) consisting of a LED diode OD 870 F (power 4.5 mW) which emits a band of 50 nm. centered on a wavelength of 870 nm.

The choice of the LED diode is due to the fact that it is easy to drive and not very sensitive to thermal fluctuations and also because it lends itself to directly support the light source which, in this way, can be placed in close contact with the skin.

To detect the signal reflected from the muscle of the stump, the aforementioned sensor (1) adopts an integrated photo detector OP 21 1 (3).

The distance between emitter and receiver, on which the maximum depth to which photons penetrate depends, is 12 mm. In order not to damage the electrical components on the sensor, its surface must be covered with waterproofing, biocompatible and hypoallergenic optical glue.

In practice, the operation of the limb prosthesis according to the invention is ensured by a pair of the aforementioned optical sensors (1), one for the agonist muscle and one for the antagonist muscle; this pair of sensors is controlled by means of the electronic circuit shown in figure 3.

In the first of these sensors the main clock is provided by an integrated LM555 which provides a square wave at 1 kHz. The pulses thus obtained are first formed by two integrated 74HC123 to have a duration of 0.1 ms and are then sent to a "Led driver" capable of providing up to 60 mA to the LED (this is the 74F3037 integrated). The light radiation diffused by the muscle tissues is then collected by an OP 211 amplified photo diode with a transimpedance gain equal to 1 Mohm.

The preamplified signal is injected into a "sample and 'hold", the command of which is always provided by the pair of 74HC123 that form it and appropriately delay starting from the square wave so that it is in phase.

The signal is sent to a voltage amplifier with the gain selectable by means of a dip-switch; it is an LF347 operational amplifier in a non-inverting configuration.

The second sensor is similar to the first just described, with the only difference that the light pulses of the first are out of phase with respect to those of the second, in order to avoid interference phenomena on the tissues. Therefore, the same main clock given by the LM555 is used, while the 74HC123 formers also produce a delay compared to the first sensor.

Finally, it should be noted that the aforementioned pair of optical sensors was connected to the power driver of the prosthetic hand using a PC equipped with an appropriate acquisition card, in order to validate its operation. The signal coming from the two sensors is digitized and amplified in order to be compatible with the input levels provided by the power driver.

In practice, the two optical sensors (la, lb) used to accompany the limb prosthesis according to the invention are positioned on the patient's stump in the same positions where the EMG electrodes of traditional prostheses are currently located and the patient is required to perform the same muscle contractions required in the use of traditional prostheses.

On the basis of appropriate experiments, it was possible to verify how the signals taken from the optical sensors supplied with the new prosthesis according to the invention are able to perfectly control the opening and closing of the prosthetic hand.

The aforementioned figure 4 allows to finally verify the practical methods of application of the aforementioned sensors (la, lb) to the aforementioned preferred embodiment of the upper limb prosthesis according to the invention.

In fact, this prosthesis (100) conventionally makes use of a socket (100a) for the installation of the abutment; the two aforementioned sensors (la, lb) are mounted inside this same socket (100a), so that one can pick up the signal produced by the agonist muscle of the stump and the other the signal produced by the antagonist muscle of the stump itself.

The socket (100a) adopted in the particular prosthesis model shown in this same figure 4 is hinged, by means of a motorized elbow (101), to the respective prosthetic forearm (102) which, in turn, ends with a motorized prosthetic hand (103).

The same prosthetic forearm (102) contains, in addition to the amplifier and the power circuit, the power supplies (104) designed to provide the energy necessary for the operation of the prosthesis in question (100).

Regardless of the fact that in the latter figure 4 a model of an upper limb prosthesis has been reproduced intended for amputated subjects just below the armpit, it is understood that the present inventive idea can find equally successful application even in the presence of different versions of upper limb prostheses, in the presence of those versions, that is, intended for subjects who have undergone amputations of the upper limb at any other level, even at the level of the wrist.

This is because also all these different upper limb prostheses are in any case equipped with that socket for the abutment which, in the context of the present invention, is intended to house the two aforementioned sensors (la, lb) adapted to function on the basis of the theory of near infrared spectroscopy.

Claims (1)

CLAIMS 1) Upper limb prosthesis, of the type with a socket (100a) for the insertion of the abutment and ending with a motorized prosthetic hand (103), characterized by the fact that it bears, in correspondence with the aforementioned socket (100a) , two optical sensors (la, lb) as described in the previous description, which are capable, exploiting the theory of near infrared spectroscopy, to detect respectively the contractions and decontractions of the agonist muscle of the stump and the contractions and decontractions of the antagonist muscle of the same stump; it is also provided that the detections of the states of contraction and decontraction of the aforementioned muscles operated by the two same sensors (la, lb) are translated, through the electronic management circuit described in the previous description, into corresponding actuation commands for the aforementioned motorized prosthetic hand (103).