EP1899603A1

EP1899603A1 - Metal hydride actuator

Info

Publication number: EP1899603A1
Application number: EP06752853A
Authority: EP
Inventors: Stephane Bedard; Martin Richard; Pierre-Olivier Roy
Original assignee: Victhom Human Bionics Inc
Current assignee: Victhom Human Bionics Inc
Priority date: 2005-06-29
Filing date: 2006-06-29
Publication date: 2008-03-19
Also published as: WO2007000058A1; CA2613563A1

Abstract

A metal hydride actuator comprising a pressure chamber having a first and second pressure chamber portions and at least one reaction chamber operatively connected to one of the first and second pressure chamber portions, the at least one reaction chamber having a temperature adjustment mechanism and containing therein metal hydride powder. A piston is positioned in the pressure chamber, the piston forming a barrier between the first and second pressure chamber portions, and a movement transmission means is operatively connected to the piston, the movement transmission means being so positioned in the first pressure chamber portion as to exit from an opening in a wall of the first pressure chamber portion. The temperature adjustment mechanism may be used to cause a change of temperature of the metal hydride powder in at least one of the reaction chamber, thereby creating a pressure differential between both pressure chamber portions, causing the piston to move.

Description

METAL HYDRIDE ACTUATOR

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefits of U.S. provisional patent application No. 60/694,683 filed June 29, 2005, which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present invention relates to a metal hydride actuator. More specifically, the present invention relates to a metal hydride actuator for use with an active prosthesis.

BACKGROUND

[0003] Various mechanisms such as electric, hydraulic or pneumatic devices have been used as actuators. Generally, actuators are used in apparatuses requiring a controllable movement such as printers, industrial automated devices or motorized prostheses.

[0004] As early as 1950, a pneumatic muscle actuator, named the

"McKibben pneumatic artificial muscle", was developed as a part of an orthotic limb system. Nowadays, in the context of motorized prostheses design, electric actuators have been the preferred technology. The primary reason for selecting electric actuators over other technologies is based on the coupling efficiency of about 90%, the coupling efficiency being the ratio of mechanical work over electrical work. Furthermore, electric actuators use a well known technology and are readily-available in both rotational and linear configurations.

[0005] The main drawbacks of the electric actuator technology are the weight of the device and the noise related to mechanical transmission. SUMMARY

[0006] The present invention relates to a metal hydride actuator, comprising:

a pressure chamber having a first and second pressure chamber portions;

at least one reaction chamber operatively connected to one of the first and second pressure chamber portions, the at least one reaction chamber having a temperature adjustment mechanism and containing therein metal hydride powder;

a piston positioned in the pressure chamber, the piston forming a barrier between the first and second pressure chamber portions; and

a first movement transmission means operatively connected to the piston, the first movement transmission means being so positioned in the first pressure chamber portion as to exit from an opening in a wall of the first pressure chamber portion;

wherein a change of temperature of the metal hydride powder in at least one of the reaction chamber by the temperature adjustment mechanism creates a pressure differential between both pressure chamber portions, causing the piston to move.

[0007] The present invention also relates to a metal hydride actuator as described above, wherein the at least one reaction chamber includes an aluminum foam containing the metal hydride, the aluminum foam being enclosed in a filter.

[0008] The present invention further relates to a metal hydride actuator as described above, wherein the temperature adjustment mechanism consists in a thermoelectrical cooler positioned in contact with the filter.

[0009] Further still, the present invention relates to a metal hydride actuator as described above, further comprising a second movement transmission means positioned in the second pressure chamber portion, the second movement transmission means being connected to the piston and positioned so as to exit from an opening in a wall of the second pressure chamber. BRIEF DESCRIPTION OF THE FIGURES

[0010] Illustrative embodiments of the invention will be described by way of example only with reference to the accompanying drawings, in which:

[0011] Figure 1 is a cross sectional view of a metal hydride actuator according to the illustrative embodiment of the present invention;

[0012] Figure 2 is a cross sectional view of a second illustrative embodiment of the metal hydride actuator;

[0013] Figure 3 is an exploded perspective view of a reaction chamber;

[0014] Figure 4 is a perspective view of the aluminum foam and filter placed between two thermoelectrical coolers (TEC);

[0015] Figure 5 is a close-up view of an aluminum foam;

[0016] Figure 6 is a cross sectional view of a third illustrative embodiment of the metal hydride actuator;

[0017] Figure 7 is a cross sectional view of a fourth illustrative embodiment of the metal hydride actuator; and

[0018] Figure 8 is an exploded perspective view of a stacked reaction chamber.

DETAILED DESCRIPTION

[0019] Generally stated, the metal hydride actuator technology described herein addresses electrical actuators limitations such as weight and noise with its use of gas pressure and the absence of a mechanical transmission. The metal hydride actuator also exhibits passive properties, such as damping and compliance, that may be exploited in the context of prosthetic applications without the addition of external mechanical component.

[0020] Referring to Figure 1 , a metal hydride actuator (100) according to an illustrative embodiment of the present invention includes a first (12) and a second (14) reaction chamber with corresponding first (16) and second (18) gas outlets operatively connecting the reaction chambers (12, 14) to a pressure chamber (20) containing a piston (22) connected to a movement transmission means (24) and seals (26, 27).

[0021] The metal hydride actuator (100) is powered by converting pressure created by hydrogen fluxes in the reaction chambers (12, 14) into linear movement of the movement transmission means (24) via the piston (22). Metal hydride powder contained in the reaction chambers (12, 14) has the chemical characteristic that it is able to absorb or desorb great amounts of hydrogen depending on temperature and pressure to which it is submitted. When the temperature of the metal hydride powder increases it desorbs hydrogen, which in turn increases the pressure. This pressure may then be used to activate the metal hydride actuator (100). Conversely, when the temperature of the metal hydride powder decreases it in turn absorbs hydrogen, which decreases the pressure.

[0022] In the illustrative embodiment shown in Figure 1 , the metal hydride actuator (100) uses a push-pull configuration. Two reaction chambers (12, 14) provide hydrogen pressure through corresponding gas outlets (16, 18) to two hermetic pressure chamber portions (32, 34) in order to either push in the direction of arrow (1) using reaction chamber (12), gas outlet (16) and pressure chamber portion (32) or pull in the direction of arrow (2) using reaction chamber (14), gas outlet (18) and pressure chamber portion (34), the piston (22) and movement transmission means (24). The movement transmission means (24) may take the form of, for example, a shaft or a fluid. In the illustrative embodiment, the movement transmission means (24) takes the form of a shaft and will be identified as such from hereinafter. However, if the movement transmission means (24) was to take the form of a fluid, it is to be understood that the pressure chamber portion (34) would include a fluid conduit, for example a below (38) as shown in Figure 2, containing the movement transmission means (24).

[0023] To activate the piston (22), the metal hydride powder in one of the reaction chambers (12, 14) is heated while the metal hydride powder in the other reaction chamber (12, 14) it is being cooled. This creates a pressure differential between both hermetic pressure chamber portions (32, 34) of the cylinder (20) on each side of the piston (22), which in turn produces a force upon the piston surfaces (22a, 22b) and moves the shaft (24).

[0024] The two hermetic pressure chamber portions (32, 34) may be sealed from each other using seals (26). Furthermore, the pressure chamber (20) may be sealed from the ambient air using seals (27) to prevent oxygen contamination of the metal hydride powder. The purpose of the piston seals (26) is to hermetically isolate each pressure chamber portions (32, 34) from one another without creating too much friction between the seal (26) and the internal wall of the pressure chamber (20). For example, Turcon® AQ-Seal® 5 from Busak+Shamban with Slydring® rings may be used to seal the two pressure chamber portions (32, 34) without creating important friction.

[0025] In an second illustrative embodiment, shown in Figure 2, the metal hydride actuator (200) is very similar to the metal hydride actuator (100) of Figure 1 , therefore only the differences will be described for concision purposes. The pressure chamber (20) of metal hydride actuator (200) may be sealed from the ambient air using metal bellow (38) instead of the seals (27) of metal hydride actuator (100), for example a bellow made out of thin (0.075 mm) taper metal washers welded together inside and outside edge-to-edge, in pressure chamber portion (34) to isolate the shaft (24) from the pressure chamber (20). A second metal bellow (36) may also be added to the other pressure chamber portion (32) so that the piston surfaces (22a, 22b) exposed to the pressure differentials have generally equal areas.

[0026] Referring to Figure 3, there is shown a possible construction of a reaction chamber (12, 14) which may be, for example, a sealed aluminum box (64) connected the gas outlet (16, 18). The reaction chamber (12, 14) includes a metal hydride powder storage structure (40) and a temperature adjustment mechanism (50). The reaction chamber (12, 14) is advantageously designed so as to maintain pressure between the temperature adjustment mechanism (50) and the metal hydride powder storage structure (40), as well as act as a heat-sink for the extra- heat of the temperature adjustment mechanism (50) and heat coming from the metal hydride exothermic reaction.

[0027] Referring now to Figure 4, the metal hydride powder storage structure (40) includes an aluminum foam (41 ), such as shown in Figure 5, in which is embedded the metal hydride powder. The aluminum foam (41) may be, for example, Duocell Aluminum Foam from ERG Aerospace with 40 pores per inch (PPI), which provides good thermal transfer. To retain the metal hydride powder within the metal hydride powder storage structure (40), the metal hydride powder permeated aluminum foam (41) is enclosed within a filter made out of micro- perforated stainless steel sheets (42) and stainless foil (44), such as 0.001 inch stainless foil. The perforated sheets (42) are located on the sides of the aluminum foam (41) to retain the metal hydride powder and leave the hydrogen free to pass through it. The stainless steel foils (44) are placed on the top and bottom of the aluminum foam (41 ), where heat is transferred. This metal hydride powder storage structure (40) favors hydrogen permeability and increases the life expectancy of the reaction chambers (12, 14). However, in an alternative embodiment, copper plated metal hydride pellets may be used but they may not sustain as many cycles due to the volume increase of the metal when absorbing the hydrogen. Metal hydride pellets may also decrease the hydrogen permeability of the reaction chambers (12, 14).

[0028] The temperature adjustment mechanism (50) is used to heat up and cool down the metal hydride powder storage structure (40). For example, the temperature adjustment mechanism (50) may take the form of a pair of thermoelectrical coolers (TEC) between which is placed the metal hydride powder storage structure (40), the TECs (50) being used to either heat up or cool down the metal hydride powder storage structure (40). Thermal grease may be applied to the stainless foil (44) to improve the thermal transfer between the TECs (50) and the metal hydride powder storage structure (40).

[0029] In order to optimize thermal conduction, a contact pressure between the TECs (50) and the metal hydride powder storage structure (40) is recommended. This pressure is recommended by TEC manufacturers to allow a good contact surface between the various parts of the TECs (50) assembly for the effective transfer of heat. Depending on the TECs (50) size and thickness, this pressure may vary.

[0030] For example, a 40 mm X 40 mm HP-199-1.4-0.8 TEC from TE

Technology would require a contact pressure from 150 to 300 PSI between the TECs (50) and the metal hydride powder storage structure (40). This means that a force between 1700 and 3400 Newton (370 to 745 LBS) should be applied to the metal hydride powder storage structure (40) and TECs (50) assembly. To achieve this force, four Vi-28 UNF screws (66) may be used to hold secure the lid (62) to the body (64) of the reaction chamber (12, 14). Fine thread screws may be used because of the resistance of their threads which provide more axial preload for a given torque. According to the "turning moment and axial load" formula of threaded fasteners, the torque applied on the ¹Λ-28 UNF screws (66), in this specific example, should be between 0.56 and 1.12 Nm (5 and 10 LBS/in).

[0031] The metal hydride actuator (100), such as illustrated in Figure 1 , may be used in a variety of applications, an example of which is for powering a knee member of an actuated leg prosthesis. For this specific application, it may be assumed that during level walking the maximum torque at the knee is approximately 0.7 Nm/kg. Based on a 70 kg person, the required torque would then be around 50 Nm, thus using a 0.1 m level arm on a three-bar mechanism, a 500 N actuator would be able to produce the required torque.

[0032] To obtain those requirements, a metal hydride actuator (100) with an effective piston (22) area of 8.56X10^"4 m² and a pressure chamber (20) length of 10 cm may be used. The amount of metal hydride powder required for each reaction chamber (12, 14) would be approximately 15 g and the total volume of the metal hydride actuator (100) would be approximately 175 cm³ (external diameter of 1.5" and length of 6").

[0033] The metal hydride actuator (100), as previously described, may also be used in a passive mode, dissipating kinetic energy. In this mode an external force pushes on the shaft (24) attached to the piston (22) in the direction of arrow (2), compressing the Hfe gas. The compression of the hb gas creates a force opposed to the movement, resulting in the metal hydride actuator (100) acting in a spring like fashion The compression of the hfe gas also results in some of the Hb gas being absorbed by the metal hydride powder, resulting in a damping of the movement. Such a behavior may be useful, for example, at the ankle were the ankle joint acts like a spring and damper for most part of the movement cycle.

[0034] Furthermore, the absorption and desorption of gas in the reactions

(12, 14) is linked to thermal heat dissipation and absorption on the TECs (50), which causes an electrical potential (voltage) between the inputs of the TECs (50). This voltage may in turn generate an electrical current. Thus, mechanical movement of the actuator (100) in a passive mode could, through the thermal process on the TECs (50), be transduced to electrical energy.

[0035] In a third illustrative embodiment, shown in Figure 6, the metal hydride actuator (300) is very similar to the metal hydride actuator (200) of Figure 2, therefore only the differences will be described for concision purposes. The metal hydride actuator (300) includes two shafts (24, 25), one on each side of the piston (22). As it may be seen, the other components of the metal hydride actuator (300) are similar to those of the metal hydride actuator (100) shown in Figure 1 and the metal hydride actuator (200) shown in Figure 2, the second shaft

(25) having been added for more versatility.

[0036] In a fourth illustrative embodiment, shown in Figure 7, the metal hydride actuator (400) is very similar to the metal hydride actuator (200) of Figure 2, therefore only the differences will be described for concision purposes. The metal hydride actuator (400) includes a single reaction chamber (12) with gas outlet (16) operatively connecting the reaction chamber (12) to the pressure chamber (32), which includes the piston (22) connected to the shaft (24), seals

(26) and bellows (36, 38). In this illustrative embodiment, unlike the previous embodiments, the metal hydride actuator (400) is simply used in a push configuration. The reaction chamber (12), which is positioned at the rear of the metal hydride actuator (400), i.e. the end opposite the shaft (24), provides hydrogen pressure through corresponding gas outlet (16) to the hermetic pressure chamber portion (32) in order to push the piston (22) and shaft (24) in the direction of arrow (3). A resilient member (39), for example a spring, provides the pull force and, for efficiency purposes, may be set such as to provide a constant force during the full stroke of the metal hydride actuator (400).

[0037] To activate the metal hydride actuator (400) and move the piston (22) and shaft (24), the metal hydride powder in the reaction chamber (12) is heated. This creates a pressure differential between both hermetic pressure chamber portions (32, 34) of the cylinder (20) on each side of the piston (22), which in turn produces a force upon the piston surface (22a) and moves the shaft (24) in the direction of arrow (3). When the reaction chamber (12) is cooled down the resilient member (39) pulls on the piston (22) and moves the shaft (24) back into an equilibrium position between the resilience of the resilient member (39) and the residual pressure in the chamber portion (32). This illustrative embodiment provides for a simpler, easier to manufacture, easier to monitor and lower cost actuator than one in a push-pull configuration.

[0038] In an alternative embodiment (not shown), one or both of the bellows

(36, 38) may have the property of being resilient, thus making possible the elimination of the resilient member (39).

[0039] In a fifth illustrative embodiment, the metal hydride actuator is very similar to the metal hydride actuator (100) shown in Figure 1 , metal hydride actuator (200) of Figure 2 or metal hydride actuator (300) of Figure 6, with the difference that both reaction chambers (12, 14) are combined into a single stacked reaction chamber (15) having a first (15a) and second (15b) reaction chamber portions, as shown in Figure 8. As mentioned previously, the TECs (50) are heat pumps which transfer energy from one side (called the cold side) to the other (called the hot side). In an energy optimization spirit, the TECs (50a, 50c, 50b) may be stacked with the metal hydride powder storage structures (40a, 40b) so as to recover some of the thermal energy and enhance system efficiency, effectively eliminating one of the TECs (50) in the process, since the TEC (50c) located between the two reaction chamber portions (15a, 15b) acts as a heater on one side and as a cooler on the other side.

[0040] However, as the metal hydride powder storage structures (40a, 40b) will mostly be at different operational pressures, they must be sealed from one another within the body (74) of the reaction chamber (15) within their respective reaction chamber portions (15a, 15b) using a seal (76) that may accept a high hydrogen pressure gradient and fast temperature cycling. In a fashion similar to the previous embodiments, the lids (72) may be used to apply the recommended contact pressure between the TECs (50a, 50c, 50b) and the metal hydride powder storage structures (4Oa₁ 40b) for an effective transfer of heat.

[0041] Advantageously, the seal (76) includes at least two separate sealing portions (not shown), in order to decrease pressure gradient due to high temperature gradient, and is made of a material well suited for thermal cycling, the material having stable mechanical properties for the whole thermal cycling range.

[0042] As mentioned previously, thermal grease may be applied to the stainless foil (44) to improve the thermal transfer between the TECs (50a, 50c, 50b) and the metal hydride powder storage structures (40a, 40b). As well, in order to optimize thermal conduction, a contact pressure between the TECs (50a, 50c, 50b) and the metal hydride powder storage structures (40a, 40b) is recommended. This pressure is recommended by TEC manufacturers to allow a good contact surface between the various parts of the TECs (50a, 50c, 50b) assembly for the effective transfer of heat. Depending on the TECs (50a, 50c, 50b) size and thickness, this pressure may vary.

[0043] It is to be understood that even though the various embodiments are schematically illustrated, it will be apparent to persons skilled in the art how to physically construct working embodiments of the present invention. [0044] Although the present invention has been described by way of illustrative embodiments and examples thereof, it should be noted that it will be apparent to persons skilled in the art that modifications may be applied to the present particular embodiment without departing from the scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A metal hydride actuator, comprising: a pressure chamber having a first and second pressure chamber portions; at least one reaction chamber operatively connected to one of the first and second pressure chamber portions, the at least one reaction chamber having a temperature adjustment mechanism and containing therein metal hydride powder; a piston positioned in the pressure chamber, the piston forming a barrier between the first and second pressure chamber portions; and a first movement transmission means operatively connected to the piston, the first movement transmission means being so positioned in the first pressure chamber portion as to exit from an opening in a wall of the first pressure chamber portion; wherein a change of temperature of the metal hydride powder in at least one of the reaction chamber by the temperature adjustment mechanism creates a pressure differential between both pressure chamber portions, causing the piston to move.

2. A metal hydride actuator according to claim 1 , wherein the first movement transmission means includes a shaft.

3. A metal hydride actuator according to claim 1 , wherein the piston includes a first seal to form a hermetic barrier between the first and second pressure chamber portions.

4. A metal hydride actuator according to claim 1, wherein the first pressure chamber includes a second seal positioned between the first movement transmission means and the opening.

5. A metal hydride actuator according to claim 1 , wherein the first pressure chamber portion includes a third seal positioned around the first movement transmission means between the piston and the opening.

6. A metal hydride actuator according to claim 5, wherein the third seal is a first bellow.

7. A metal hydride actuator according to claim 5, wherein the first movement transmission means includes a fluid and a fluid conduit.

8. A metal hydride actuator according to claim 6, wherein the first bellow is resilient.

9. A metal hydride actuator according to claim 6, further comprising a second bellow positioned in the second pressure chamber portion between the piston and a wall of the second pressure chamber.

10. A metal hydride actuator according to claim 9, wherein at least one of the first and second bellows is resilient.

11.A metal hydride actuator according to claim 1 , wherein the at least one reaction chamber includes an aluminum foam containing the metal hydride powder.

12.A metal hydride actuator according to claim 11, wherein the aluminum foam is enclosed in a filter.

13. A metal hydride actuator according to claim 12, wherein the filter consist of perforated stainless steels sheets located on the sides of the aluminum foam and stainless steel foils on the top and bottom of the aluminum foam.

14. A metal hydride actuator according to claim 13, wherein the temperature adjustment mechanism consists in a first thermoelectrical cooler positioned in contact with the stainless steel foil located on top of the aluminum foam and a second thermoelectrical cooler positioned in contact with the stainless steel foil located on the bottom of the aluminum foam.

15. A metal hydride actuator according to claim 14, wherein there is thermal grease between the first thermoelectrical cooler and the stainless steel foil located on top of the aluminum foam and between the second thermoelectrical cooler and the stainless steel foil located on the bottom of the aluminum foam.

16. A metal hydride actuator according to claim 14, wherein the first thermoelectrical cooler is pressed into contact with the stainless steel foil located on top of the aluminum foam at a pressure of about 150 to 300 PSI and the second thermoelectrical cooler is pressed into contact with the stainless steel foil located on the bottom of the aluminum foam at a pressure of about 150 to 300 PSI.

17. A metal hydride actuator according to claim 1 , wherein the temperature adjustment mechanism consists in at least one thermoelectrical cooler.

18. A metal hydride actuator according to claim 1 , further comprising a second movement transmission means positioned in the second pressure chamber portion, the second movement transmission means being connected to the piston and positioned so as to exit from an opening in a wall of the second pressure chamber.

19. A metal hydride actuator according to claim 18, wherein the second movement transmission means includes a shaft.

20. A metal hydride actuator according to claim 18, wherein the second movement transmission means includes a fluid and a fluid conduit.

21. A metal hydride actuator according to claim 1 , further comprising a resilient member positioned in the second pressure chamber portion between the piston and a wall of the second pressure chamber portion.

22.A metal hydride actuator according to claim 21 , wherein the resilient member includes a spring.

23.A metal hydride actuator according to claim 1 , wherein the at least one reaction chamber includes: a first reaction chamber operatively connected to the first pressure chamber portion; and a second reaction chamber operatively connected to the second pressure chamber portion.

24.A metal hydride actuator according to claim 1 , wherein the at least one reaction chamber includes a reaction chamber having a first reaction chamber portion operatively connected to the first pressure chamber portion and a second reaction chamber portion operatively connected to the second pressure chamber portion

25.A metal hydride actuator according to claim 24, wherein the first pressure chamber portion includes a first aluminum foam containing metal hydride powder and the second pressure chamber portion includes a second aluminum foam containing metal hydride powder.

26.A metal hydride actuator according to claim 25, wherein the first aluminum foam is enclosed in a first filter and the second aluminum foam is enclosed in a second filter.

27.A metal hydride actuator according to claim 26, wherein the first and second filter consist of perforated stainless steels sheets located on the sides of the first and second aluminum foams and stainless steel foils on the top and bottom of the first and second aluminum foams.

28.A metal hydride actuator according to claim 27, wherein the temperature adjustment mechanisms consists in: a first thermoelectrical cooler positioned in contact with the stainless steel foil located on top of the first aluminum foam; a second thermoelectrical cooler positioned in contact with the stainless steel foil located on the bottom of the first aluminum foam and in contact with the stainless steel foil located on the top of the second aluminum foam; and a third thermoelectrical cooler positioned in contact with the stainless steel foil located on the bottom of the second aluminum foam.

29. A metal hydride actuator according to claim 28, wherein there is thermal grease between the first thermoelectrical cooler and the stainless steel foil located on top of the first aluminum foam, between the second thermoelectrical cooler and the stainless steel foil located on the bottom of the first aluminum foam, between the second thermoelectrical cooler and the stainless steel foil located on the top of the second aluminum foam, and between the third thermoelectrical cooler and the stainless steel foil located on the bottom of the second aluminum foam.

30. A metal hydride actuator according to claim 29, wherein the first and second reaction chamber portions are sealed from each other using a seal.

31. A metal hydride actuator according to claim 30, wherein the seal has a high hydrogen pressure gradient and fast temperature cycling.

32.A metal hydride actuator according to claim 31 , wherein the seal includes at least two separate sealing portions.