This invention relates generally to a power generating method and system that uses body energy from gait to operate electronic prosthetic or orthotic devices.
Artificial joints generally require mechanisms to control their movement. For example an artificial knee joint or prosthetic joint will be prescribed for a person with a through-knee (TK) or an above-knee (AK) amputation. i.e. a person without a knee joint, shank or foot. The ability for the knee to bend or articulate during sitting, kneeling or ambulating is desirable. It is also desirable to have the ability to control the leg during the swing and stance-phases of gait when the person is walking or running.
The “swing-phase control” refers to the control of the joint's movement or articulation during the swing-phase of the gait cycle to make the gait more efficient and more natural looking. Traditionally fluid-based pneumatic or hydraulic dampers are used in prosthetics to help control the swing-phase. With these devices, the control is initially tuned to suit the walking patterns of the amputee. However, if the amputee significantly alters his/her walking pattern, the knees will require further adjustment on the part of the prosthetist. Furthermore, fluid-based dampers tend to be complex and susceptible to leaks.
Microprocessor-controlled, electronically or computer controlled prostheses all utilize feedback control to better adapt to changes in the amputee's gait, and continually adjust the level of damping. This facilitates a more natural and efficient gait for individuals with above-knee amputations. Several devices are currently on the market. The Blatchford Endolite Intelligent prostheses use a pneumatic damper that is continually adjusted to provide optimal damping for swing-phase control. The C-leg prosthesis uses a microprocessor-controlled hydraulic damper for both swing-phase and stance-phase control. The Rheo knee uses a similar approach, but instead of hydraulic fluid, it uses magnetorheological fluid. One drawback of these technologies is that the user must charge the on-board batteries on a daily basis. A second drawback is that the systems tend to be heavy and bulky, in part due to the battery packs.
Historically, the application of pneumatic and hydraulic dampers for prosthetic swing-phase control has been successful because controlling motions at the knee joint can be done very well by applying torque passively. This means that energy is dissipated in pneumatic and hydraulic dampers predominantly in the form of heat. However, instead of dissipating the energy, it is possible to convert and store the energy, so that it may power the electronics in microprocessor-controlled prostheses. This eliminates the need for large and heavy battery packs, and also the inconvenience associated with daily charging of batteries.
The use of physiological energy to charge batteries and/or power electronic devices has mainly been applied to able-bodied gait, and in the form of generators located in the shoe. These are described in several patents namely U.S. Pat. Nos. 6,182,378 and 6,255,799, JP Patent Nos. 2001327197 and JP2006014572, and CN Patent Nos. 1202340, CN 1541582 (2004), and CN1707904 (2005).)
The object of one aspect of the present invention is to provide a means for using body energy from the gait to provide power to electronic prosthetic or orthotic systems. An alternative objective is to provide a means for using body energy from the gait to provide swing-phase damping. Another objective it is to provide concomitantly power to electronic prosthetic systems and swing-phase damping
In accordance with one aspect of the present invention there is provided an artificial knee joint with a means to generate electrical current from the motions (activities) of the prosthesis or orthosis during walking, jogging or running For convenience, an electromechanical generator such as a DC motor is applied to a knee joint, so that relative motions between the tipper (thigh) and lower (shank) portions of the knee joint will drive the motor rotor. A transmission means, such as a gear assembly, is used to amplify the motions at the knee joint. in order to increase the rotor speed, and facilitate the generation of adequate levels of current. This electrical current may be used to recharge onboard batteries, or directly to power the electronics of a microprocessor-based prosthesis, by way of example only and therefore eliminating the need for a battery pack.
The other aspect of the invention relates to the use of the generator namely a geared motor to provide damping. By decreasing the electrical resistance between the motor terminals, generated current is allowed to flow back into the geared motor. This increases the resistance in the motor, in effect causing the motor through the transmission to act as a damper.
In one application, a smaller geared motor can be used in a microprocessor-based prosthesis or orthosis for mainly current generation, to supply power to the electronics and/or to keep onboard batteries charged. This would be applicable to prosthetic technologies that use electronics, such as the aforementioned commercially-available microprocessor-based knee joints.
In another application. a larger geared motor can be used to provide damping, much like a pneumatic or hydraulic damper. This may be applicable to conventional prosthetic technologies that do not use electronics and as a substitute for more costly and higher-maintenance hydraulic or pneumatic dampers. Preferably a variable resistor would be used to tune the amount of current that is redirected back into the motor, and ultimately the damping level, much like adjusting the valve on a hydraulic or pneumatic damper. Finally, a larger geared motor may be used to generate power to supply the electronics in a microprocessor controlled knee joint, and in addition provide a means for damping.
The device could be based on an electromagnetic, piezoelectric or other type of means of electrical current generation. It may by used to power any type of prosthesis that uses electronics, and hence requires a supply of power. The device may be applied at any prosthetic or orthotic joint for example at the knee, ankle, elbow, hip or shoulder, and may generate electrical current during the swing-phase of gait, stance-phase of gait, or both phases. For example tie passive moments at the prosthetic ankle during stance can be used to generate electrical current for a microprocessor-based prosthetic knee joint In a single prosthesis.
A detailed description of the preferred embodiments is provided herein below by way of example only with reference to the following drawings, in which:
In the drawings, preferred embodiments of the invention arc illustrated by way of example. It is to be expressly understood that the description and drawings are only for the purpose of illustration and as an aid to understanding, and are not intended as a definition of the limits of the invention
The following description relates to the preferred embodiments of the present invention for a generator in a prosthetic or orthotic joint. In accordance with a preferred embodiment of the present invention there is provided a generator for a prosthesis having a means for generating electrical current using body energy transmitted to the prosthesis. Body energy may be further defined as energy emanating from activities from the body such as mechanical, vibrational, psychological, thermal, ultrasonic (sound waves via muscles), or biochemical body energy, current by way of example only, that is then transmitted to the prosthesis and converted into an electrical current. The mode of transmission of the body energy to the prosthesis may vary depending an the type of body energy being generated. For example, mechanical body energy may be generated and transmitted by the movement of the body or through a force being exerted within the body.
The means for generating electrical current using body energy transmitted to the prosthesis may be further defined as a means for converting body mechanical energy adapted to engage the prosthesis to generate an electrical current. The means for generating electrical current using body energy transmitted to the prosthesis further includes a transmission means adapted to engage the prosthesis to generate the electrical current by the means for converting body mechanical energy.
The means for generating electrical current using body energy transmitted to the prosthesis may also be defined as an electromechanical generator and the means for converting body mechanical energy may be defined as an electromechanical motor. A brushed direct current (DC) motor may be used. The transmission means may be a gear assembly that allows for the amplification of the body energy transmitted to the prosthesis. The electromechanical generator can further provide damping to control the movement of the prosthesis. Specifically a simple electronic circuit can be used to vary how much generated current is allowed to flow back into the geared motor. For example, by connecting the negative and positive terminals of a brushed direct current motor, in effect achieving a short circuit, the maximum level of damping is achieved. Therefore, as the motor rotor is mechanically driven this motion is resisted by a high damping torque which increases as the driving speed of the rotor increases. Conversely, minimal damping torque is achieved by disconnecting the terminals of the motor, so that an open circuit is achieved. When the motor is mechanical driven in this open circuit setup, there is minimal damping torque resisting the motion of the motor. Finally the current generated by the means for generating electrical current using body energy transmitted to the prosthesis may also be used to power electronics in a microprocessor-controlled prosthesis.
The means for generating electrical current using body energy transmitted to the prosthesis may also be defined as a piezoelectric generator or an electromagnetic generator by way of example only. The current generated by the means for generating electrical current using body energy transmitted to the prosthesis may be used to facilitate the operation of the prosthesis. For example the current may be used to recharge onboard batteries or be used to power electronics in a controlled prosthesis.
In one embodiment, the geared motor is located in the shank portion [2] of the prosthetic knee joint and the output shaft is linked by gears [6] to the thigh portion [3] of the knee prostheses (
Due to the oscillatory nature of the knee motion during walking, resulting from knee flexion and extension cycles. the current generated is alternating. A rectifying circuit is needed to convert it to direct current so that it can be used by the electronics or to charge the batteries. As the amputee walks with this device, pulses of current are generated, corresponding to peak knee flexion and knee extension angular velocities.
The charging characteristics of the geared motor as shown in
In order to maximize charging current. a number of design parameters can be affected. The gear ratio should be selected to maximize rotor speed. The gear ratio should however not be as high so as to exceed the maximum rated speed for the motor, or prevent back driving of the motor. Gear ratios between 50 and 500 may be optimal. The specifications of the motor can also influence the power generated. A larger motor will generally produce more current. A motor with a higher velocity constant (i.e. a motor that runs at a higher voltage) will generate a higher potential across the terminals, at lower rotor speeds when mechanically driven. This will decrease the threshold for charging, for example, from 200 deg/s to 100 deg/s. The threshold speed can also be decreased by using a lower voltage battery pack, for example four 1.2 V cells (total of 4.8 V) that might adequately power a 3.7 V microprocessor circuit. The reduction in threshold can also be accomplished by charging batteries in parallel, so that for example in the design presented here the threshold would be based on 1.2 V. A reduced threshold allows longer pulses of charging current, and a smoother charging profile.
The generator may be designed into existing systems. for example a microprocessor controlled hydraulic based swing-phase/stance-phase controller such as the C-leg. An example of this is presented in
The geared motor can also be utilized for adaptable swing-phase damping, as mentioned above. the mechanisms would generally be applied as in
Other variations and modifications of the invention are possible. All such modifications or variations are believed to be within the sphere and scope of the invention as defined by the claims appended hereto.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CA2007/001624 | 9/17/2007 | WO | 00 | 3/11/2009 |
Number | Date | Country | |
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60844669 | Sep 2006 | US |