WO2015170964A1

WO2015170964A1 - A prosthetic limb integrated with a sensory system

Info

Publication number: WO2015170964A1
Application number: PCT/MY2015/050032
Authority: WO
Inventors: Nur Azah HAMZAID; Amr Mohammed EL-SAYED
Original assignee: Universiti Malaya
Priority date: 2014-05-09
Filing date: 2015-05-08
Publication date: 2015-11-12

Abstract

The present invention relates to a prosthetic limb (200) integrated with a sensory system (100), comprising of a prosthetic socket (210) for receiving an amputee stump; a lever arm; and an actuator (220); characterized in that said sensory system (100) comprises of a sensing element (120) mounted on the prosthetic socket (210); and a controller (110) connected to the sensing element (120) and the actuator (220), for estimating a gait phase and sending an input signal to the actuator (220) to produce the prosthetic limb (200) movement. The present invention also provides a method of producing the prosthetic limb (200) movement, characterized by the steps of transmitting information from the sensing element (120) to the controller (110); estimating the gait phase using the controller (110), thereby creating the input signal based on the information received from the sensing element (120); sending the input signal from the controller (110) to the actuator (220) to produce the prosthetic limb (200) movement.

Description

A PROSTHETIC LIMB INTEGRATED WITH A SENSORY SYSTEM

Background of the Invention

Field of the Invention

This invention relates to a prosthetic limb, and more particularly to a prosthetic limb integrated with a sensory system for estimating an intended gait phase of an amputee.

Description of Related Arts

Conventional powered artificial limbs, or myoelectric prostheses, as they are more commonly referred to, are notorious for having control problems. These conventional prostheses are equipped with basic controllers that artificially mobilize the joints without any interaction from the amputee and are only capable of generating basic motions. Such basic controllers do not take into consideration the dynamic conditions of the working environment, regardless of the fact that the prosthesis is required to generate appropriate control within a practical application. They are generally lacking in predictive control strategies necessary to anticipate the artificial limb's response as well as lacking in adaptive regulation enabling the adjustment of the control parameters to the dynamics of the prosthesis. Because human limb mobility is a complex process including voluntary, reflex and random events at the same time, conventional myoelectric prostheses do not have the capability to interact simultaneously with the human body and the external environment in order to have minimal appropriate functioning. According to amputees, specific conditions of use of conventional leg prostheses such as repetitive movements and continuous loading typically entail problems such as increases in metabolic energy expenditures, increases of socket pressure, limitations of locomotion speeds, discrepancies in the locomotion movements, disruptions of postural balance, disruptions of the pelvis-spinal column alignment, and increases in the use of postural clinical rehabilitation programs. U. S. Patent Publication 201 10137429 A1 disclosed a control system being combined with an autonomous actuated prosthesis for amputees. It is particularly well adapted for use with an actuated leg prosthesis for above-knee amputees. Unlike conventional prostheses, these autonomous actuated prostheses are designed to supply the mechanical energy necessary to move them by themselves. The purpose of the control system is to provide the required signals allowing to control an actuator. To do so, the control system is interfaced with the amputee using artificial proprioceptors to ensure the coordination between the amputee and the movements of the actuated prosthesis. The set of artificial proprioceptors captures information, in real time, about the dynamics of the amputee's movement and provides that information to the control system. The control system is then used to determine the joint trajectories and the required force or torque that must be applied by the actuator in order to provide coordinated movements. However, the set of artificial proprioceptors in the cited art may be lack of quality assurance, sensitivity, and specificity while measuring the mechanical forces created by high acceleration movement.

Another example such as U. S. Patent Publication 20080065225 A1 disclosed sensors for utilization in prosthetic implants and prosthetic trials. The present invention encompasses intelligent implants incorporating sensors operative to measure distributed forces at such joints as the femorotibial and patellofemoral joints. The cited art may include a series of microsensing elements ("array") and a micropump fabricated using semiconductor or MEMS (microelectromechanical systems) fabrication technology. The sensors may be arranged in an array of sensing elements that are externally powered by either electromagnetic induction or radio frequency (RF) induction or internally powered using a battery or other power storage device. Data representative of that generated by the sensors is remotely transmitted using RF technology. Pressure sensing elements, temperature sensing elements, and chemical sensing elements may be included in each sensor array in order to provide a more complete picture for an attending physician during, and subsequent to, surgery. The sensor array includes sensors detecting at least one of a predetermined component, a predetermined contaminant, and a predetermined property. The plurality of sensors includes at least one of resistive microcantilevers, piezoelectric microcantilevers, and microcapacitor sensors. In a more detailed embodiment, the prosthesis includes a knee replacement femoral prosthesis and the sensor array is embedded within the knee replacement femoral prosthesis. However, the drawback of this cited art includes a plurality of types of sensor arrays such as pressure sensing elements, temperature sensing elements, and chemical sensing elements which may add an additional weight to the prosthesis. Besides, there are many systems available to help replace the function of an amputated knee to allow the amputees to regain their ability to perform near normal gait patterns on even ground and moderately rough terrain. But, when it comes to using stairs and changing from a sitting to standing position, the amputees are taught to adopt compensatory strategies that emphasize the use of the remaining leg to achieve those tasks. More often than not, these strategies and movements consume more energy than what would be consumed if the amputee has the ability to actively control their prosthetic knee to flex and extend to overcome those obstacles. Furthermore, the increased use of the remaining leg will put it at risk of early onset of osteoarthritis and stress fractures of the foot due to the increased weight being applied to it.

Accordingly, it can be seen in the prior arts that there exists a need to provide a prosthetic incorporated with sensors to detect the mechanical forces applied by the amputees' residual limb onto the socket in order to deduce what the amputee intends to do so as to improve the amputee's gait.

Summary of Invention

It is an objective of the present invention to provide a prosthetic incorporated with sensors to detect the mechanical forces applied by the amputees' residual limb onto the socket in order to deduce what the amputee intends to do so as to improve the amputee's gait. It is also an objective of the present invention to provide a controller which can classify the prosthetic limb motion based on the information from a sensor placed inside a prosthetic socket, which is derived from the muscle mechanical contraction and ground reaction forces.

Accordingly, these objectives may be achieved by following the teachings of the present invention. The present invention relates to a prosthetic limb (200) integrated with a sensory system (100), comprising of a prosthetic socket (210) for receiving an amputee stump; a lever arm; and an actuator (220); characterized in that said sensory system (100) comprises of a sensing element (120) mounted on the prosthetic socket (210); and a controller (1 10) connected to the sensing element (120) and the actuator (220), for estimating a gait phase and sending an input signal to the actuator (220) to produce the prosthetic limb (200) movement. The present invention also provides a method of producing the prosthetic limb (200) movement, characterized by the steps of transmitting information from the sensing element (120) to the controller (1 10); estimating the gait phase using the controller (1 10), thereby creating the input signal based on the information received from the sensing element (120); sending the input signal from the controller (1 10) to the actuator (220) to produce the prosthetic limb (200) movement.

Brief Description of the Drawings

The features of the invention will be more readily understood and appreciated from the following detailed description when read in conjunction with the accompanying drawings of the preferred embodiment of the present invention, in which:

Fig. 1 a is a diagram showing a prosthetic limb integrated with a sensory system;

Fig. 1 b is a diagram showing a signal conditioning circuit of sensing element;

Fig. 2 is a flow chart showing the sensory system estimates a gait phase of the prosthetic limb; Fig. 3 is a stick diagram showing a heel strike motion performed by an amputee; Fig. 4 is the stick diagram showing a flat foot motion performed by the amputee;

Fig. 5 is the stick diagram showing a toe off motion performed by the amputee;

Fig. 6 is the stick diagram showing a stair ascends motion performed by the amputee;

Fig. 7 is the stick diagram showing a sit to stand motion performed by the amputee.

Detailed Description of the Invention

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for claims. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims. As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words "include," "including," and "includes" mean including, but not limited to. Further, the words "a" or "an" mean "at least one" and the word "plurality" means one or more, unless otherwise mentioned. Where the abbreviations or technical terms are used, these indicate the commonly accepted meanings as known in the technical field. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures. The present invention will now be described with reference to Figs. 1 a-7.

The present invention relates to a prosthetic limb (200) integrated with a sensory system (100), comprising of:

a prosthetic socket (210) for receiving an amputee stump;

a lever arm (230) connecting the prosthetic socket (210) to an actuator (220) for actuating a movement of the prosthetic limb (200);

characterized in that said sensory system (100) comprises of:

a sensing element (120) mounted on the prosthetic socket (210) for detecting interaction forces generated between the prosthetic socket (210) and the amputee stump; and

a controller (1 10) connected to the sensing element (120) and the actuator (220), for estimating a gait phase and sending an input signal to the actuator (220) to produce the prosthetic limb (200) movement.

In a preferred embodiment of the prosthetic limb (200) integrated with the sensory system (100), the sensing element (120) is a force sensing resistor or a piezoelectric sensor. In a preferred embodiment of the prosthetic limb (200) integrated with the sensory system (100), the gait phase comprises heel strike, foot flat, toe-off, stair ascend, and sit to stand movements.

In a preferred embodiment of the prosthetic limb (200) integrated with the sensory system (100), the sensing element (120) is mounted on an inner surface of the prosthetic socket (210).

In a preferred embodiment of the prosthetic limb (200) integrated with the sensory system (100), the sensing element (120) is mounted at an anterior rectus femoris region of the prosthetic socket (210). In a preferred embodiment of the prosthetic limb (200) integrated with the sensory system (100), the sensing element (120) is mounted at a posterior biceps femoris region of the prosthetic socket (210). In a preferred embodiment of the prosthetic limb (200) integrated with the sensory system (100), the sensing element (120) is mounted at an anterior rectus femoris region and a posterior biceps femoris region of the prosthetic socket (210).

The present invention also provides a method of producing the prosthetic limb (200) movement by using the prosthetic limb (200) integrated with the sensory system (100) according to claim 1 , characterized by the steps of:

transmitting information from the sensing element (120) to the controller

(1 10);

estimating the gait phase using the controller (1 10), thereby creating the input signal based on the information received from the plurality of sensing elements (120); and

sending the input signal from the controller (1 10) to the actuator (220) to produce the prosthetic limb (200) movement. In a preferred embodiment of the method of producing the prosthetic limb (200) movement by using the prosthetic limb (200) integrated with the sensory system (100), wherein the information detected by the sensing element (120) is analysed by the controller (1 10) based on maximum value of amplitude voltage, minimum value of amplitude voltage, standard deviation of amplitude voltage and average of amplitude voltage, number of slope sign changes, and any combination thereof.

Below is an example of a prosthetic limb (200) integrated with a sensory system (100) from which the advantages of the present invention may be more readily understood. It is to be understood that the following example is for illustrative purpose only and should not be construed to limit the present invention in any way. Examples

A prosthetic limb (200) has a prosthetic socket (210) for receiving an amputee stump. In a preferred embodiment, the prosthetic socket (210) can be made of various materials and in different sizes, but preferably custom-made for each amputee according to the shape and condition of the residual amputee stump and the amputee's mobility grade.

A lever arm (230) connects the prosthetic socket (210) to an actuator (220) for actuating a movement of the prosthetic limb (200). In a preferred embodiment, the actuator (220) is preferably a pneumatic actuator, having an electric motor coupled with a sliding spindle (221 ) and revolute joint on a knee chassis. In a preferred embodiment, the lever arm (230) is connected to the actuator (220) by the sliding spindle (221 ). The sliding spindle (221 ) slidably is received within a spindle slider connector. The sliding spindle (221 ) is connected to a spindle nut (222) that controls the sliding spindle (221 ) to slide along one axis to perform a linear motion of the prosthetic limb (200) as shown in Figure 1 a. The prosthetic limb (200) further includes a fail-safe feature in which the prosthetic limb (200) will become a free moving passive limb or will fully extend in the case of a system failure or a loss of power supply. This will allow the amputee some level of mobility and stability to get to a safe place to assess a problem or to get help.

Figure 1 a is a diagram showing the prosthetic limb (200) integrated with a sensory system (100). The prosthetic limb (200) is integrated with the sensory system (100) for detecting amputee's intention movement in order to achieve a more responsive gait as well as improve abilities beyond normal walking such as stair climbing and hill descent. Said sensory system (100) is a communication mechanism connecting the sensing element (120), the controller (1 10), and the actuator (220). The sensing element (120) is preferably mounted on an inner surface of the prosthetic socket (210). In a preferred embodiment, the sensing element (120) is preferably disposed at an anterior rectus femoris region of the prosthetic socket (210), and at a posterior biceps femoris region of the prosthetic socket (210). Generally, placing the sensing element (120) in these two regions (biceps and rectus femoris) should be sufficient in detecting the amputee's intention for movement. Adding the sensing element (120) onto those regions at both proximal and distal regions of the prosthetic socket (210) may give a more accurate reading for estimation of a gait phase.

In a preferred embodiment, the sensing element (120) is preferably a force sensing resistor or a piezoelectric sensor. The force sensing resistor measures force or pressure exerted by the amputee and requires power supply, such as from a battery, to function. The piezoelectric sensor is an active element and it does not require an external power source and an amplification circuit to measure the force exerted by the amputee.

In a preferred embodiment, the force sensing resistor is connected to a signal conditioning circuit (121 ) to acquire an output amplitude voltage from the force sensing resistor. The signal conditioning circuit (121 ), as illustrated in Figure 1 b, is to provide output amplitude voltage. The signal conditioning circuit (121 ) may be connected to Simulink environment using Real-Time Windows target toolbox. A data acquisition system (e.g. Advantech PCI-1710HG) is utilized to analyze the output from the force sensing resistor.

In a preferred embodiment, the sensing element (120) has minimal thickness to maintain comfort in the prosthetic socket (210) of the prosthetic limb (200) without limiting the natural movement of the amputee. Said sensing element (120) has a preferred thickness of less than 1 .25 mm.

The sensing element (120) sends information via the signal conditioning circuit (121 ) to the controller (1 10). Said controller (1 10) is preferably a microcontroller. In a preferred embodiment, the information is of the measured interaction forces generated between the inner surface of the prosthetic socket (210) and the amputee stump. The information detected by the sensing element (120) and then analysed by the controller (1 10) based on a plurality of factors comprising maximum value of amplitude voltage, minimum value of amplitude voltage, average and standard deviation of amplitude voltage, and number of slope sign changes at each gait phase for both anterior and posterior regions. The controller (1 10) receives the information from the sensing element (120) and estimates the gait phase based on the information received. Having estimated the gait phase, the controller (1 10) determines the correct command for the actuator (220) to produce the desired prosthetic limb (200) movements. The command is sent as an input signal from the controller (1 10) to the actuator (220). In a preferred embodiment, the gait phase comprises heel strike, foot flat, toe-off, stairs ascend, and sit to stand movements.

Experimental trials on amputee

The amputee is instructed to perform the gait phase such as heel strike, foot flat, toe off, stair ascend, and sit to stand movements separately, each within a one second period. The voltage output from the sensing element (120) is acquired and plotted against time (in milliseconds) using MATLAB software. The sensing element (120), in this example is preferably a force sensing resistor, is first placed at the rectus femoris in the anterior region of the prosthetic socket (210) and the amputee performs each gait phase while wearing the prosthetic limb (200). Then, the sensing element (120) is placed at the biceps femoris at the posterior region of the prosthetic socket (210) and each gait phase is repeated.

Heel strike (contact phase)

A heel strike is a stage in a gait at which the heel of the foot or shoe first makes contact with the walking surface or ground. The amputee is required to stimulate the heel strike by landing his heel on the ground. Without the rest of the feet coming into contact with the ground, he is then required to lift his heel off the ground. Figure 3 is a stick diagram showing the heel strike motion performed by the amputee. This motion is performed repeatedly over a one second period. Foot flat (support phase)

In this phase, the foot progresses from initial heel contact to the loading of the rest of the feet. The amputee assumes a position with the heel planted on the ground before plantar flexing the entire foot to the ground. Figure 4 is a stick diagram showing the flat foot motion performed by the amputee. This motion is performed repeatedly over a one second period without lifting of the heel. Toe off (propulsive phase)

This is the final stage of the walking gait where the toes propel the amputee forward as the foot is pushed off from the ground. From the foot flat position, the amputee lifts up the heel followed by the toes in a standard walking motion. Figure 5 is a stick diagram showing the toe off motion performed by the amputee. This motion is performed repeatedly over a one second period.

Stair ascent

Amputee's leg is in flexion position rested upon an elevated step. The amputee is required to apply force downward, simulating a stair ascending motion. Figure 6 is a stick diagram showing the stair ascent motion performed by the amputee. This motion is performed repeatedly over a one second period.

Sit-to-stand

Ambulating from a seated position to a full upright standing position is an important movement for any amputee in their daily activities. In this trial, the amputee is requested to sit on a chair, stand, and return to a sitting position. Figure 7 is a stick diagram showing the sit-to-stand motion performed by the amputee. This motion is performed repeatedly over a one second period. Experimental result

The information produced from the sensing element (120) is transmitted to the controller (1 10) and analysed by an identification process performed by a classifier of the controller (1 10). The information sent by the sensing element (120) comprises sensor measurements made by the sensing element (120) in the anterior and posterior regions of the prosthetic socket (210). Said information is analysed based on the plurality of factors comprising maximum value of amplitude voltage, minimum value of amplitude voltage, average and standard deviation of amplitude voltage, and number of slope sign changes at each gait phase for both anterior and posterior regions of the prosthetic socket (210). Two separate parameter measurements for both anterior and posterior regions provided useful information for estimating the intended gait phase. A set of reference data is stored in the controller (1 10), to identify the direction and nature of the movement during the different phases. A control algorithm in the controller (1 10) could be further programmed to compare the information collected from the sensing element (120) with the reference data stored in the controller (1 10) to determine the intended movement of the prosthetic limb (200) and then send the input signal to the actuator (220) by adjusting the specific motion required by the controller (1 10), whether to flex or extend based on the information delivered from the sensing element (120).

Table 1 shows the reference data of the parameters measured at each phase of the prosthetic limb movement. Number of slope sign changes is to be addressed at different points, which may provide an indication about the frequency content. A set of rules as shown in Figure 2 is used to determine whether the information collected matches with correct gait phase of knee movement.

Table 1 : Reference data of parameters measured at anterior and posterior regions at different gait phase of knee movements.

Heel strike Foot flat Toe off Stair ascent Sit to stand

Maximum values (Volts)

Anterior 3.1 3.2 3.12 3.22 3.02

Posterior 3.18 3.19 3.19 3.188 3.2

Minimum values (Volts)

Anterior 2.67 3.02 2.66 3.05 2.78

Posterior 2.97 3.02 2.92 3.05 2.91

Average (standard deviation)

Anterior 2.8 (+0.13) 3.04 (+0.09) 2.8 (+0.14) 3.09 (+ 0.05) 2.8 (+0.1)

Posterior 3.03 (+0.08) 3.08 (+0.08) 3.06 (+0.1) 3.09 (+0.05) 3.03 (+0.09)

Number of slope sign changes

Anterior 1 2 1 1 3

Posterior 1 2 2 2 2

The controller (1 10) performs the other arithmetic operations that help the controller (1 10) to adapt the prosthetic limb movement. The estimation of the intended movement is done by configuring out values of average and standard deviation at each phase. For instance as shown in Table 1 , the stair ascent phase shows minimal values of standard deviation, 0.05, of the sensor measurements at both anterior and posterior regions compared to the other movements. In contrast, the foot flat phase shows standard deviation values of 0.09 and 0.08 at the anterior and posterior respectively. The sensory system (100) therefore displays good accuracy for the stair ascent and foot flat phases. However, the rest of the movements display greater standard deviation values.

Different movements that have been performed and the capability of the sensory system (100) in detecting various gait phase of the knee movement, a decision flow chart illustrates the procedure of the detection of the knee events as shown in Figure 2. The algorithm of the detecting the five gait phases that have been studied in the present invention is presented. The first stage of the algorithm begins with reading the information of the sensor measurements sent by the sensing element (120). Then, the controller (1 10) identifies the gait phase based on the number of slope sign changes of the sensor measurements. For instance, if the slope sign changes once at the posterior region, this denotes that the knee is at the heel strike phase. Two or three slope sign changes at the anterior region indicate the foot flat phase and sit-to-stand phase respectively. Briefly, three gait phases might be determined at the first stage (for example heel strike, foot flat, and sit-to-stand) without going through the next stage, which reveals minimal complexity in computing and good response time.

If the number of slope sign changes detected at the anterior region is one and the number of slope sign changes at the posterior region is two, then the algorithm proceeds to a second stage. The second stage of the algorithm is to consider both the number of slope sign changes measured at the anterior and posterior regions together with the average and standard deviation values of the sensor measurements. If the number of slope sign changes equals to two at the posterior region, while the average and standard deviation of the sensor measurements are 3.08 and 0.08 respectively, the gait phase is estimated to be the foot flat phase. If the number of slope sign changes at the anterior region is one while the average and standard deviation are 2.8 and 0.13 respectively, the gait phase is estimated to be the heel strike.

In the second stage of the algorithm, two factors would affect the output decision of the algorithm, such as the number of slope sign changes at the posterior or anterior regions and the average and standard deviation values of the sensor measurements. The prior computation will affect the time response of the system and may produce unacceptable delay. The experiment can be repeated by employing different prosthetic socket types and different types of the sensing element (120), such as piezoelectric sensors. Although the present invention has been described with reference to specific embodiments, also shown in the appended figures, it will be apparent for those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined in the following claims.

Description of the reference numerals used in the accompanying drawings according to the present invention:

Reference

Description

Numerals

100 Sensory system

1 10 Controller

120 Sensing element

121 Signal conditioning circuit

200 Prosthetic limb

210 Prosthetic socket

220 Actuator

221 Sliding spindle

222 Spindle nut

230 Lever arm

Claims

Claims I/We claim:

1 . A prosthetic limb (200) integrated with a sensory system (100), comprising of:

a prosthetic socket (210) for receiving an amputee stump;

characterized in that said sensory system (100) comprises of:

2. The prosthetic limb (200) integrated with the sensory system (100) according to claim 1 , wherein the sensing element (120) is a force sensing resistor or a piezoelectric sensor.

3. The prosthetic limb (200) integrated with the sensory system (100) according to claim 1 , wherein the gait phase comprises heel strike, foot flat, toe-off, stair ascend, and sit to stand movements.

4. The prosthetic limb (200) integrated with the sensory system (1 00) according to claim 1 , wherein the sensing element (120) is mounted on an inner surface of the prosthetic socket (210).

5. The prosthetic limb (200) integrated with the sensory system (100) according to claim 1 , wherein the sensing element (120) is mounted at an anterior rectus femoris region of the prosthetic socket (210).

The prosthetic limb (200) integrated with the sensory system (100) according to claim 1 , wherein the sensing element (120) is mounted at a posterior biceps femoris region of the prosthetic socket (210).

The prosthetic limb (200) integrated with the sensory system (100) according to claim 1 , wherein the sensing element (120) is mounted at an anterior rectus femoris region and a posterior biceps femoris region of the prosthetic socket (210).

8. A method of producing the prosthetic limb (200) movement by using the prosthetic limb (200) integrated with the sensory system (100) according to claim 1 , characterized by the steps of:

transmitting information from the sensing element (120) to the controller (1 10);

sending the input signal from the controller (1 10) to the actuator (220) to produce the prosthetic limb (200) movement.

9. The method of producing the prosthetic limb (200) movement by using the prosthetic limb (200) integrated with the sensory system (100) according to claim 8, wherein the information detected by the sensing element (120) is analysed by the controller (1 10) based on maximum value of amplitude voltage, minimum value of amplitude voltage, standard deviation of amplitude voltage and average of amplitude voltage, number of slope sign changes, and any combination thereof.