ARTIFICIAL HUMANOID ROBOTIC HAND AND PROCESS OF MANUFACTURING THEREOF
FIELD OF INVENTION
[001] The embodiments herein generally relate to a robotic hand with flexibility  dexterousness and load capacity analogous to the human hand for industrial and medical applications. More specifically  it relates to an artificial humanoid robotic hand and process of manufacturing such robotic hand that uses air pressure and asymmetric tube or bellow actuator with suitable reinforcement for an effective and low-cost robotic mechanism.
BACKGROUND OF THE INVENTION
[002] The human hand is capable of a wide range of movements  from lifting heavy objects to the tiniest of tools and having flexibility to grip around the object to hold it securely. The human hand has been mimicked by many robotic hands to provide the same range of movements and flexibility. Robotic hand can be used in industries to lift heavy objects  in medical science to provide prosthetic hand or assist in surgery  in situations wherein objects can be lifted from places dangerous or places unreachable to humans  in space applications as well as in nuclear plants. A perfect robotic hand should be compact  light-weight  sturdy and cost-effective and be able to be used in both industrial and commercial applications. However  there are a few hurdles to overcome for a robotic hand to be able to mimic a human hand in all aspects.
[003] A robotic hand needs to be flexible to be able to wrap the fingers securely around an object as well as sturdy for secured gripping. For flexibility of the “fingers” of a robotic hand to hold an object securely  many of the conventional robotic hands or grippers are formed of a (rigid structure) material so as to enable enough deformity for flexible movements of the fingers and enough rigidity to hold the object securely. However  such rigid materials do not impart high enough flexibility  therefore  deformation is not as flexible as desired and also the gripping strength required.
[004] To provide flexibility and mimic the finger movements of a human hand  in many robotic hands  the fingers are connected to wires or artificial muscles which are connected to microprocessors through pulleys or pressure control valves that control the finger movement. In many such robotic hands  sensors are also provided to sense the location of the object or force required to lift the object. To mimic a human hand is difficult; and to induce movement and flexibility of a particular joint in the robotic finger  wires  pulley  gears  motors  power supply  control means and microprocessors are required. This in turn makes the movement of the robotic fingers complex  the arrangement of the different components in the robotic hand makes it bulky and therefore  dexterity is lost. Compactness of a robotic hand is directly proportional to dexterity. A robotic hand wrapped in too many wires effect its dexterity. Also  usually spaces are provided for additional lengths of wire incase of a snag. These not only occupy space but additional cables make the hand expensive as well as bulky. Most importantly  these robotic hands cannot be used for industrial applications that require more sturdy hands as a slight snag in one of the numerous wires would render the hand useless; therefore making maintenance of these robotic hands a priority and elevating the cost expenses.
[005] In industrial application  wherein robotic hands are used to lift and transfer heavy objects  the rigidity/robustness of the hand must be kept in mind. Therefore  most of the robotic hands used in industrial purposes have claws made of heavy metal that provides no flexibility/deformity at all. The claws cannot deform in compliance with the object. Since most of these claws can grasp objects of definite shape only  therefore  different claws need to be used to lift objects of different shape and therefore  these claws need to be changed every time objects of different shapes need to be lifted.
[006] Most of these robotic hands used in industries are larger in size and not feasible for installation in a small-scale factory having a smaller work space. Also  small robotic hands would be preferred for doing many of the small labor jobs (like transferring objects) in industries for which manual labor is currently used. However  these labor-saving robotic hands are not preferred as they are expensive and are not a feasible investment in a small scale factory.
[007] In order to develop robotic hands that can grip well and are also flexible  and can be used across various platforms  many scientific research papers have been published wherein several kinds of pneumatic rubber actuators have been developed and reported with two or more internal chambers having symmetric cross section as shown in Fig 1. The figure illustrates a rubber actuator 100 having three internal chambers 101  each measuring 120°. Also their internal pressures are controlled independently through the flexible tubes  which are connected to pressure control valves. However  because of the numerous cross sections in the tube  the control mechanism becomes complicated. Also  the robotic hand devised is quite expensive making it commercially infeasible.
[008] Some scientists have also started research on the dexterous hand design and fabrication in their laboratories. Some of them are artificial hand using artificial muscles. The artificial hands actuated by pneumatic artificial muscle are costly and difficult to miniaturize.
[009] Fluidic actuators have impeded the design of artificial actuation systems due to their relatively high weight and low power and particularly suitable for macro-robotics compared to other actuator technologies.
[0010] Therefore  there is a need in the art for providing a robotic hand that does not require much wiring or flexible tubes to supply fluid  provides deformity  can be used across all industries and is also cost-effective. Further  there is a need for method of manufacturing the flexible tubes used for robotic hand.
OBJECTS OF THE INVENTION
[0011] A main object of the present invention is to provide an artificial humanoid robotic hand.
[0012] Another object of the present invention is to develop a robotic hand by using asymmetric tubes or asymmetric bellows made of either flexible nitrile rubber or polymer or metallic or combination of both.
[0013] Still another object of the present invention is to provide a robotic hand that can grasp objects of varying dimensions securely.
[0014] Yet another object of the present invention is to provide a robotic hand that has improved finger flexibility to enable objects to be grasped securely.
[0015] Another object of the present invention is to provide a robotic hand that is cost-effective.
[0016] Another object of the present invention is to provide a robotic hand that can be used across numerous applications  including lifting objects in industries and as a prosthetic in the medical field.
[0017] Another object of the present invention is to provide a robotic arm that is actuated by a simple pressure mechanism to perform actions precisely and reliably.
[0018] Another object of the present invention is to provide for a robotic hand that can be easily manufactured.
[0019] Another object of the present invention is to provide for a robotic hand that is compact and slender and can be miniaturized because of its simple structure.
[0020] Another object of the present invention is to provide for a robotic hand that has many degrees of freedom and high power density.
[0021] Another object of the present invention is to provide for a robotic hand that can be operated smoothly and frictionless mechanism.
[0022] Another object of the present invention is to provide for a robotic hand that can be easily serviced and maintained.
[0023] Yet another object of the present invention is to provide a method of manufacturing the asymmetric tubes or bellows used for the robotic hand.
[0024] The other objects and advantages of the present invention will be apparent from the following description when read in conjunction with the accompanying drawings which are incorporated for illustration of preferred embodiments of the present invention and are not intended to limit the scope thereof.
SUMMARY OF THE INVENTION
[0025] In view of the foregoing  an embodiment herein provides an artificial humanoid robotic hand and a process of manufacturing asymmetric tube for the robotic hand. The robotic hand can grasp objects securely and the fingers of the hand can deform and wrap around an object of any shape to hold it securely. Such a robotic hand is obtained by using Asymmetric Flexible Pneumatic Actuators (AFPA) as fingers. Accordingly  the robotic hand includes plurality of asymmetric tubes or bellows that are configured as “fingers” or ‘finger joints’ of the robotic hand. These fingers are controlled by an electro-pneumatic pressure control system that controls the amount of internal pressure to be applied to the fingers to make them coil or bend around a particular object. The internal pressure fluid could be pneumatic (air) or hydraulic (oil  water  etc) depending on the type of application the hand is used. For light weight application pneumatic pressure is preferred.
[0026] As an alternative to asymmetric tube actuators  asymmetric bellow actuators which imitate the joints of a human hand can also be used. These actuators can be constructed to have a side bent joint as well as a spherical joint. The design of the thumb and the non-thumb fingers are such that the entire hand  as a whole  provides 23 degrees of freedom including the wrist joint of a palm. In this way  a dexterous robotic hand can be made that can imitate the human hand closely and is also flexible  low-priced and of simple construction.
[0027] The configuration of AFPA and a process of manufacturing the same are disclosed herein. For manufacturing the asymmetric tubes  rubber  chemicals and oil in specific ratios are mixed. To mix the components  rollers are used which roll in opposite directions to each other. Raw rubber is passed in between these two rollers and a band is formed on one of the roller. The other components are added one after the other. Once mixing of all the components is complete  the next step in the process is pre-forming wherein the sheets of rubber compound produced from the first step of mixing is cut to the required shape so that the sheet suitably fit to the mould during the molding process. Moulds are made of two halves of required shape/thickness and a center pin of the required size of the hole is located eccentrically in the mould. Preformed compound rubber is placed in the mould and pressure is applied on the mould to form the asymmetric rubber tube actuators or AFPAs.
[0028] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood  however  that the following descriptions  while indicating preferred embodiments and numerous specific details thereof  are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof  and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The detailed description is set forth with reference to the accompanying figures. In the figures  the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items.
[0030] Fig 1 shows the symmetric pneumatic flexible micro actuator (FMA) made of rubber of the prior art that has two or more internal chambers with fiber reinforcement.
[0031] Fig 2 shows the cross sectional view of asymmetric flexible pneumatic actuator (AFPA) used for robotic hand  with cotton yarn and spring steel wire or strip reinforcement according to an embodiment herein;
[0032] Fig 3a shows the AFPA before being subjected to pressure  according to an embodiment herein;
[0033] Fig 3b shows cross sectional diameter of the AFPA before being subjected to pressure  according to an embodiment herein;
[0034] Fig 3c shows the AFPA after being subjected to pressure  according to an embodiment;
[0035] Fig 3d shows cross sectional diameter of the AFPA after being subjected to pressure  according to an embodiment herein;
[0036] Fig 4(a) shows an end-momenter attached eccentrically to an AFPA   according to an embodiment herein;
[0037] Fig 4(b) shows an end-momenter attached eccentrically to a symmetric FPA   according to an embodiment herein;
[0038] Fig 5a shows the full-asymmetric flexible bellow actuators  according to an embodiment herein;
[0039] Fig 5b shows bending of the full- asymmetric flexible bellow actuators under pressure  according to an embodiment herein;
[0040] Fig 5c shows various types of reinforcement in AFPA  according to an embodiment herein;
[0041] Fig 5d  Fig 5e shows various types of gripping configuration using asymmetric flexible tube  according to an embodiment;
[0042] Fig 6a shows half- asymmetric flexible bellow actuator  according to an embodiment herein;
[0043] Fig 6b shows bending of the half- asymmetric flexible bellow actuator under pressure  according to an embodiment herein;
[0044] Fig 7 shows the joints of a human hand  according to an embodiment herein;.
[0045] Fig 8(a) shows the left side sway bend of the bellow actuators  according to an embodiment herein;
[0046] Fig 8(b) shows the right side-sway bend of the actuators  according to an embodiment herein;
[0047] Fig 9 shows the design of the bending joint based on asymmetric flexible bellow  according to an embodiment herein;
[0048] Fig 10 shows the design structure of the thumb  according to an embodiment herein;
[0049] Fig 11 shows the design structure of the non-thumb finger  according to an embodiment herein;
[0050] Fig 12 shows bending joint using single AFPA (1DOF)  according to an embodiment herein;
[0051] Fig 13 shows sway joint using two AFPA (2 DOF)  according to an embodiment herein;
[0052] Fig 14 shows spherical joint using three AFPA (3DOF)  according to an embodiment herein;
[0053] Fig 15 shows a simple four-fingered robotic hand  according to an embodiment herein;
[0054] Fig 16 shows a model of Artificial Humanoid Robotic hand based on AFPA as finger joints  according to an embodiment herein; and
[0055] Fig 17 shows a model of Artificial Humanoid Robotic hand covered with silicone rubber material based on AFPA  according to an embodiment herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0056] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly  the examples should not be construed as limiting the scope of the embodiments herein.
[0057] As mentioned  there remains a need for developing an artificial humanoid robotic hand that does not require much wiring  provides deformity  can be used across all industries and is also cost-effective. The embodiments herein achieve this by providing a robotic hand includes plurality asymmetric tube or bellow actuators which can be configured as ‘fingers’ or ‘finger joints’ of the robotic hand. Referring now to the drawings  more particularly to Figs 1 through 17  where similar reference characters denote corresponding features consistently throughout the figures  there are shown preferred embodiments.
[0058] According to an embodiment of the present invention  the robotic hand includes plurality of asymmetric tube or bellow actuators that are configured as “fingers joint” of the robotic hand. The asymmetric tube having variable wall thickness is illustrated in Fig. 2. The asymmetric tube or bellow actuator can also be referred herein as asymmetric flexible pneumatic actuator (AFPA). In an embodiment  the AFPA is made of a rubber or nitrile rubber  plastic or polymer or synthetic material of non-circular cross section. In an embodiment  the AFPAs are closed at one end and since they are asymmetrically molded  whenever pressure is applied  the “fingers” start bending in a desired direction Thus when an object needs to be grasped  on application of pressure at one end of these AFPAs  the fingers bend  grasping the same securely.
[0059] The working principle of the robotic hand by using the AFPAs is illustrated with the help of Fig 3a to 3d  according to an embodiment. Fig 3a shows the asymmetric tube before being subjected to pressure  Fig 3b shows cross sectional diameter of the asymmetric tube before being subjected to pressure  3c shows the asymmetric tube after being subjected to pressure  and Fig 3d shows cross sectional diameter of the asymmetric tube after being subjected to pressure. According to an embodiment  the fluid pressure 305 is applied to the tube 301 of asymmetric thickness and the asymmetric tube 301 would tend curve in the portion where the tube’s diameter 302 has greater thickness 303  as illustrated in Fig 3c. The thinner side 304 would expand more than the thicker side 303 because of differential expansion of the tube at various points due to asymmetry of cross-section and also end moment induced due to eccentricity.
[0060] The AFPA is configured as finger joint [similar to interphalangeal (IP)  metacarpophalangeal (MCP) and wrist joints in human hand (as shown in Fig.7] in the robotic hand of the present invention. To this end  the robotic hand consists of several “fingers” to facilitate easy grasping of an object. These fingers are essentially combination of tubes of asymmetric and symmetric diameters. AFPA provides flexibility at the joints and placed in between two symmetric rigid tubes made of plastic or synthetic or metallic material. The arrangement could be similar to the structure of the human hand. Whenever fluid pressure is applied to these fingers  they grasp the object due to their human like structure. The tubes or bellows are arranged in a manner such that they form power grasp and precision grip and such a manner that helps the fingers to grasp the object securely.
[0061] According to an embodiment  the flexible robotic hand of the present invention is operated by a pneumatic/ hydraulic system with a single internal chamber and controlled by a single motor. To apply desired fluid pressure  for each finger  the pressure is controlled independently through micro-valves for each joint of the AFPA.
[0062] Whenever an object needs to be grasped  the pneumatic/ hydraulic system pressurizes the AFPAs which bend under pressure until it firmly grasps the same. Therefore  the robotic hand of the present invention has the flexibility to adapt the object form with tactile sensing capability.
[0063] According to an embodiment of the present invention  “end-momenters” can be used to increase the end moment deliberately. The bending of the AFPA is due to the combined effect of differential expansion and the end moment that results from the asymmetric cross section. To enhance the effect  end momenters can be used which can be a simple cylinder with constant eccentricity or of variable eccentricity attached to the asymmetric tubes. Fig 4a shows an end momenter 401 attached eccentrically to an asymmetric tube actuator 301  according to an embodiment. Further  if a tube with uniform cross section is attached to the end momenter  it also curls up mainly due to the eccentricity of the force to the tube axis. Fig. 4b shows an end-momenter attached to symmetric flexible tube pneumatic actuator  according to an embodiment. The combination of end momenters and symmetric flexible tube form a new kind of bending joint which can also be used to construct the humanoid finger.
[0064] Fig 5 c shows various types of reinforcement used in AFPA  according to an embodiment. In one embodiment  a steel flat spring material can be reinforced at the thicker side of the actuator to enhance the strength of the asymmetric tube actuator. Likewise  a wide range of materials like steel strips  chains  linkage mechanisms with hinges/pin joints  inserts  wires and ropes  fibers  belts etc can be used with suitable end clamping and supporting structure for reinforcements in the asymmetric tube actuator.
[0065] In another embodiment  special self locking and releasing arrangement for enhancing the reliability of operations can be provided. Accordingly  some of the end locks which can be used in locking the end of the tube actuator after curving/gripping the object are belts-clips  steel plate-magnets  chain arrangement– springs  strap used in watch-nylon  catch/latch etc. These arrangements would provide safety to the objects while they are in transit.
[0066] In one embodiment  bellows can be used instead of tubes  as shown in Fig 5a. The bellow actuators 501 with asymmetric cross section would behave similar to the asymmetric tube actuator 301 but would have higher flexibility and greater rate of expansion and bending under internal pressure. After the internal pressure 502 is pumped in  the bellows 501 would bend as shown in Fig 5b. The bellow actuators can be used to form finger joints in the robotic hand similar to the interphalangeal joints in human hand  according to an embodiment.
[0067] In an embodiment of the present invention  the hand or gripper design could be for operation using compressed air or liquids (oil  water etc) to generate fluid pressure inside the AFPA.
[0068] In one embodiment of the present invention  the gripper design of the AFPA could be normally curved and gripping a particular object and releases the object in the application of internal pressure and can get ready for the next gripping as shown in Fig. 5d.
[0069] In another embodiment of the present invention  the gripper design of the AFPA is normally straight but on application of internal pressure  the AFPA grasps the object as shown in Fig. 5e. Such grasping can be achieved irrespective of the shape of the object.
[0070] In yet another embodiment of the present invention  the gripper design of the AFPA can use a combination of the above two embodiments for a specific application.
[0071] In an embodiment of the present invention  for automatic detection of an object  a force sensor can be attached to the AFPA such that the “fingers” can sense the nearness of an object and grasps it according to its shape.
[0072] The bellow actuator with asymmetric cross section would behave similar to the asymmetric tube actuator but would have higher flexibility and greater rate of expansion and curving under internal pressure. Bellows can be made asymmetric in cross section either with full bellow or half bellow. Figure 6 shows bending of asymmetric flexible bellow actuator subjected to internal pressure  according to an embodiment.
[0073] Bellows can be used to form finger joints similar to the interphalangeal joints in human hand  according to an embodiment. In the case of human hand  except thumb which has single interphalangeal (IP)  metacarpophalangeal (MCP) and carpometacarpal (CMC) joints  other four fingers have two IP joints called as proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints and one MCP joint to provide 25 DOFs as shown in Figure 7.
[0074] The AFPA can be used as IP joint similar to the human finger  according to an embodiment. To simulate the joints suitable for the design of multi-fingered dexterous hand  the AFPA is made to the length of 20 mm with yarn reinforcement in the circumferential direction of the bellow actuator. This would resist deformation in the radial direction. Spring Steel wire or strip may be used at the thicker side to provide strength/rigidity and helps in returning quickly to the original state when the bellow actuator is deflated. In this way  a single AFPA can be used as IP (interphalangeal) joint similar to the human finger.
[0075] Construction of side sway joint: According to an embodiment  to get the abduction-adduction movement at the metacarpophalangeal (MCP) joint of the finger  side-sway joint based on two AFPA can be constructed. Supplying the pressure of compressed air in any one of AFPAs  the two AFPAs would bend either right or left side as shown in Fig 8(a) and 8(b). In an embodiment  if the pressure is applied to left AFPA  the joint would bend to the right side and vice versa as shown in Figures 8(a) and 8(b). When deflating the AFPA  the side-sway joint would return to its original state.
[0076] Construction of spherical joint: According to an embodiment  if the three tubes are fixed to the cover plate at the ends in such a way that they form 120º between any two AFPAs and air pressure is controlled independently  they can form a spherical joint. The spherical joint can bend or yaw in any direction opposite to that of pressurized AFPA. The spherical joint can be constructed at wrist of the palm and give hyper-extension movements.
[0077] Design of the bending joint: In a preferred embodiment  for the IP (interphalangeal) joint of the fingers of the hand  bending joint based on asymmetric flexible bellow shown in the Figure 9 is used. The advantage is that the design is more compact and accommodates the supply air pipes which run from base to top segment of all the joints.
[0078] Design of Thumb: Human thumb is made of 6 DOF. According to an embodiment  a 4 DOF thumb is designed based on the combination of bending and side-sway joints as shown in Figure 10. It is composed of four joints such as Joint I  joint II  and joint III are bending joints and joint IV is the side-sway joint. These joints are connected to the polyurethane tubes or aluminium tubes which act rigid links or bones (phalanx) similar to the human fingers. The axes of joints I  II and III are almost in a straight line. The axis of the joint III is shifted and perpendicular to the axis of joint IV which is placed horizontally. To measure the angular deformation of the joint  a flex sensor is attached to the bending joint. To determine the stable grasp or manipulation of the hand  a tactile or touch sensor is placed at the bottom portion of the rigid links. In order to describe the working principle of the thumb  Joint I and joint II respectively simulate the DIP (distal interphalangeal) and PIP (proximal interphalangeal) joints of human hand. When air pressure inside AFPAs of these two joints is adjusted properly  bending movement of top segment and middle segment can be realized. Joint III and joint IV are added to simulate the MCP joint of human hand realizing bending movement and side-sway movement of the base segment.
[0079] Design of non-Thumb Fingers: According to an embodiment  except the thumb  the other four 4-DOF fingers of AFPA hand have the same structure except that the length of each finger varies similar to the human fingers. In order to distinguish from thumb  the other four fingers are called as non-thumb fingers. The design structure of non thumb finger is shown in Figure 11. It also consists of four joints. Joint I  joint II and joint III are bending joints and the joint IV is the side-sway joint. The axes of three bending joints are almost coinciding. The axis of joint III is parallel to the axis of joint IV which is shifted to one side and placed vertically. The working principle of the non-thumb is similar to the thumb.
[0080] Design of Multi-fingered hand: According to an embodiment  multi-fingered palm and the hand are designed based on the construction of joints using AFPA. The fingers are located by five fingers installing seats which are fixed inside the palm by thread connection. It has five fingers  one palm and 23 degrees of freedom including the wrist joint. In one embodiment  the multi-fingered dexterous hand can be moulded entirely and covered with artificial skin made of silicone rubber to get an approximate similar texture of the human hand as shown in Fig 17.
[0081] In this way  a multi-fingered hand has been designed based on asymmetric flexible bellow actuator. In another embodiment of the present invention  the asymmetric flexible rubber bellow actuators can be replaced with asymmetric flexible metallic bellows for light and heavyweight industrial applications based on pneumatic or hydraulic systems. The hand constructed with this kind of bellow joint will have advantages of low price  simple structure and perfect flexibility.
[0082] The method of manufacturing the asymmetric tubes or bellows are of utmost importance as each tube or bellow needs to be of an asymmetric diameter and should be molded in a particular manner. Various materials like rubber  plastic  neoprene  nitrile rubber etc can be used for the tubes; though  synthetic rubber is found to be more effective than natural rubber.
[0083] For manufacturing the asymmetric tubes  rubber  chemicals and oil in specific ratios are mixed in a certain ratio  according to an embodiment. To mix the ingredients  rollers can be used which roll in opposite directions to each other. Raw rubber is passed in between these two rollers and a band is formed on one of the roller. The other components are added one after the other. Once mixing of all the components is complete  the rubber compound is kept for about 24 hours for better wetting of chemicals. The next step in the process is pre-forming wherein the sheets of rubber compound produced from the first step of mixing is cut to the required shape so that the sheet suitably fit to the mould during the molding process. Moulds are made of two halves of required shape/thickness and a center pin of the required size of the hole is located eccentrically in the mould. This mould is placed between the platens and heated. After heating the mould  the mould is opened and the preformed compound rubber is placed in the mould and the platens are closed. Thereafter  pressure is applied on the mould and the rubber compound is cooled. The platens are then opened and an asymmetric tube composed of the rubber compound is thus formed.
[0084] According to an embodiment  the manufacturing process of an asymmetric tube made of nitrile rubber is explained in detail. Accordingly  the manufacturing process can be followed in four phases namely mixing  pre-forming  molding and finishing.
[0085] In an embodiment  during the mixing process  different components in different ratios are mixed to form the rubber compound. For instance  a table of the various components recipes to produce the AFPA along with their specific weights is listed below:
Description PHR

Nitrile rubber 100
Sulpher 2.3
Zinc oxide 5
Stearic acid 2
Antioxidant – HS 1
Paraffin wax 1
FEF 50
DOP 6
China clay 20
C I Resin 3
Accelerator MBTS 1.2
Accelerator TMTD 0.2
Total 191.7
Table 1: Compound Recipe for the asymmetric tubes
[0086] The compositions can be formulated using standard techniques known to the person skilled in the art. To facilitate the mixing  a mixing mill can be used. Mixing mill is a two roll mill where the rollers rotate in opposite directions in a friction ratio for example about 1: 1.45. Due to friction with each other  the rollers tend to get heated; therefore  to cool the rollers  cold water can be circulated through the centre of the roller with a rotary joint mechanism. Further  a hood is provided over the rollers to collect any suspended particles during mixing. The temperature at which mixing is performed is selected in-between 60 – 80°C and the duration of mixing is around 45 minutes to 60 minutes  according to an embodiment.
[0087] According to one embodiment  to mix the various components  raw rubber  in this case  nitrile rubber is fed in between the two rollers until a band is formed over one of them. Once the band is formed  the other components are added sequentially  one after the other. Simultaneously  oil is added for better mixing of the components. Initially antioxidants  activators are added. Then fillers like carbon black  china clay  takifiers are added. Tackifiers like wood rosin  Cumarone indane resins are also added for better tackiness  according to an embodiment. Along with this  processing aids like paraffin wax etc  are added for better dispersion of chemicals in the rubber compound. In the end  curing agents and accelerators are added. For better dispersion of the chemicals  whenever the chemicals are added  the rubber sheet is cut from one side to other and re-fed to the rollers. After the rubber compound is thus mixed  it is kept for a minimum period of about 22 to 26 hrs for better wetting of chemicals in the rubber mix.
[0088] In one embodiment  after the mixing phase is completed  the aged rubber compound is re-warmed in the mixing mill. The rubber compound is sheeted to the required thickness and is cut to the required shape. If required  additional sheets are cut to obtain the required weight and rolled or placed one over the other. The pre-sheet should be such that it suitably fits the mould during the molding process.
[0089] Mixed compound is aged for a minimum period of 8 hrs. Then the compound is warmed in the mixing mill and sheeting is done preferably in calendar machine to the required thickness. This calendered sheet is cut to the required shape and size of the product to be produced. Small mandrel of required diameter is taken to the lathe machine. Preformed rubber layer is placed and wound over the mandrel uniformly. Layer is cleaned with toluene solvent to remove any dust or dirt. For reinforcement  cotton yarn of required count is wound over the mandrel by maintaining 20 rounds per inch. One more layer of preformed rubber sheet is placed over the wound mandrel and wrapped. Then the tube consisting of inner rubber layer  yarn and outer rubber layer is removed from the mandrel and taken to the molding operation. After performing of the tube  weighing is done to ensure the required weight. Adjustment in the weight is done if required by placing a small piece of rubber sheet.
[0090] Compression molding technique is used for the molding of the rubber component to asymmetric tubes or bellows  according to an embodiment. A hydraulic press where the bottom plate moves upward by a hydraulic cylinder is used for the same. It consists of two platens  one at the top and the other at the bottom  and both these platens are heated by electrical heaters and normal curing temperature ranges can be from 140 to 150 °C. Moulds for molding the asymmetric tubes or bellows are placed in between the platens. They consist of two halves of required shape made up of two EN-8 material placed together inside the platens. A center pin  the diameter of which corresponds to the required size of the hollow of the asymmetric tube  is inserted inside the mould and is placed eccentrically. The mould  thus placed in between the platens is heated to the required temperature of about 150°C. Once the moulds are thus heated at the required temperature  they are opened and a mould spray is sprayed so that the final product is released from the mould easily. For example  Dilute Silicon Emulsion can be used as a lubricant for smooth release of the final product from the mould.
[0091] The preformed pieces are then placed in the mould  the platens are closed and pressure of about 30 to 35 kg/cm2 is applied on the mould by hydraulic press to force the preformed sheet to fill up the entire mould cavity  according an embodiment. Curing of the rubber component takes place inside the mould and it takes around 8 to 10 minutes to cure the component. After the cure time is over  the platens are opened and the component is ejected out of the mould.
[0092] According to an embodiment  once the final rubber component in the shape of an asymmetric tube or bellow is ejected out of the mould  the excess rubber component at the parting line is removed by scissors and cleaned. Inspection is carried out to check the dimensions and for any defects  thus the AFPA is produced.
[0093] Process of using AFPA in robotic hand: Each AFPA is considered as a “finger or bending joint of a finger ” for the robotic hand  according to an embodiment. It can be used as interphalageal(IP)  metacarpophalangeal(MCP) or wrist joints similar to human hand joints. Fig 12 shows bending joint using single AFPA (1DOF)  Fig 13 shows sway joint using two AFPA (2 DOF) and Fig 14 shows spherical joint using three AFPA (3DOF) are formed  according to an embodiment. Thus  for a simple four-fingered robotic hand as shown in Fig 15  four AFPAs produced using the above process are used. For the purpose of experiment  a robotic hand consisting of four AFPAs each 12mm in diameter and having four degrees of freedom were connected to an electro-pneumatic pressure control system. The electro-pneumatic pressure apparatus controls the amount of pressure to be applied to the fingers to enable them to grasp an object securely. Similarly a five fingered artificial humanoid robotic hand can be manufactured using the combination of the above mentioned AFPA joints to form the finger structure of the hand. Fig.-10 and 11shows the thumb and non thumb fingers of hand. Figure-16 shows the assembly of the fingers to form the artificial human hand. As pressure is applied  the fingers deform around the object to grasp it  thereby  mimicking the human hand.
[0094] Neoprene as AFPA: As mentioned hereinbefore  several materials can be used as AFPA. For the purpose of experiments  neoprene was also used as an AFPA  wherein two symmetric tubes of same length but different diameters were cut along its length and adhered to each other and circumferentially covered with transparent tape to avoid bulging  thus the symmetric tubes became asymmetric having thicker side at the bottom and thinner side at the top. No fibers were reinforced except that a steel flat spring material was reinforced at the thicker side of the actuator to enhance the strength of the asymmetric tube actuator. The free end of the tube actuator was closed. From the experiments  it was seen that when the AFPA was subjected to varying internal hydraulic pressure  the radius of curvature decreased from infinity to a minimum value as the fluid pressure increased and the tube bends 360º at a certain pressure. It is also seen that as the length of the tube actuator increases curling also increases to two or more rounds. Also  it has been observed that larger size actuators bend more as compared to smaller size actuators for the same amount of internal pressure because the internal force is more in a larger diameter tube actuator.
[0095] In an alternative embodiment of the present invention  the asymmetric tube or bellows can also be used in pressure gauge to measure the pressure.
[0096] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can  by applying current knowledge  readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept  and  therefore  such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore  while the embodiments herein have been described in terms of preferred embodiments  those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Abstract:
In view of the foregoing  an embodiment herein provides an artificial humanoid robotic hand and a process of manufacturing asymmetric tube or bellows for the robotic hand. The robotic hand can grasp objects securely and the fingers of the hand can deform and wrap around an object of any shape to hold it securely. Such a robotic hand is obtained by using Asymmetric Flexible Pneumatic Actuators (AFPA) as fingers or finger joints of a multi-fingered dexterous hand. Accordingly  the robotic hand includes plurality of asymmetric tubes or bellows that are configured as “fingers or finger joints” of the robotic hand. These fingers are operated by a single motor and controlled by an electro-pneumatic pressure control system that controls the amount of internal pressure to be applied to the fingers to make them coil or bend around a particular object. A method for manufacturing the asymmetric tube is also disclosed.
FIG.2

We Claim:
1. An artificial humanoid robotic hand for grasping an object comprising of
plurality of asymmetric flexible pneumatic actuator [AFPA] configured as finger joints of the robotic hand; wherein said asymmetric tube actuator is provided with variable wall thickness and closed at one end of said asymmetric tube actuator.
2. The robotic hand of claim 1  wherein said AFPA is asymmetric flexible tube actuator or asymmetric flexible bellow actuator.
3. The robotic hand of claim 2  wherein said AFPA is made from a material group comprises of rubber  plastic  polymer  neoprene  nitrile  flexible metallic or combination of any.
4. The robotic hand of claim 3  wherein end-momenters can be used in said AFPA to increase the end moment deliberately.
5. The robotic hand of claim 3  wherein said AFPA strength can be enhanced by reinforcing a steel flat spring material at the thicker side of the said AFPA.
6. The robotic hand of claim 3  wherein said AFPA strength can be enhanced by reinforcing special self locking and releasing arrangement at the thicker side of the said AFPA.
7. The robotic hand of claim 3  wherein internal pressure is applied inside said AFPA to bend said finger joint thereby enabling to grasp an object.
8. The robotic hand of claim 7  wherein said pressure is controlled independently through micro-valves for each joint of the AFPA  wherein said AFPA is operated by a pneumatic/ hydraulic system with a single internal chamber and controlled by a single motor.
9. The robotic hand of claim 8  wherein the hand could be made as a multi-fingered humanoid robotic hand or gripper depending on the application requirement based on the said AFPA.
10. The robotic hand of claim 8  wherein gripper design of said AFPA is straight and on application of internal pressure  said AFPA tends to bend for grasping an object.
11. The robotic hand of claim 8  wherein gripper design of said AFPA is straight can be curved and gripping an object normally  wherein on application of internal pressure said AFPA can release the object.
12. The robotic hand of claim 8  wherein a single AFPA can be used as IP (interphalangeal) joint similar to the human finger.
13. The robotic hand of claim 8  wherein side-sway joint based on two AFPA can be constructed to get the abduction-adduction movement at the metacarpophalangeal (MCP) joint of the finger.
14. The robotic hand of claim 8  wherein three AFPA are fixed at 120º between any two AFPAs to form spherical joint  wherein the spherical joint can bend or yaw in any direction opposite to that of pressurized AFPA  wherein the spherical joint can provide hyper-extension movements at the wrist joint of the palm.
15. A method of manufacturing asymmetric flexible pneumatic actuator [AFPA] comprising the step of
mixing nitrile rubber  chemicals and oil in predetermined ratios in two rollers;
allowing to keep said mixed compound at normal temperature for a predetermined duration for better wetting of chemicals;
performing said mixed compound to cut into desired shape of sheet which can suitably fit into molding machine;
molding said preformed sheet in molding machine to form an AFPA.
16. The method of manufacturing AFPA of claim 14  wherein said chemicals comprises of sulpher  zinc oxide  stearic acid  antioxidant-HS  paraffin wax  FEF  DOP  china clay  C I resin  accelerator MBTS  and Accelerator TMTD.
17. The method of manufacturing AFPA of claim 14  wherein said mixing is performed about 45 to 60 minutes at a temperature in the range of about 60 to 80°C.
18. The method of manufacturing AFPA of claim 14  wherein said molding is performed by using compression molding technique  wherein said molding machine comprises of two platens wherein between mould is placed  and a center pin having diameter equivalent to the required size of the hollow of the AFPA is inserted inside the mould and is placed eccentrically  wherein said mould is heated at required temperature in the range of 140 to 150 °C.
19. The method of manufacturing AFPA of claim 17  wherein said preformed sheets are placed in said mould  and said platens are closed to pressure at about 30 to 35 kg/cm2 by using hydraulic press to force the preformed sheet to fill up the entire mould cavity.
20. The method of manufacturing AFPA of claim 18  wherein curing of said sheet takes place inside the mould to form final rubber compound in the shape of an asymmetric  wherein said curing can take place around 8 to 10 minutes  wherein the platens are opened to eject the AFPA.
21. An artificial humanoid robotic hand substantially as herein described and illustrated with reference to and with the help of forgoing examples and accompanying drawings.
22. An asymmetric flexible pneumatic actuator [AFPA] substantially as herein described and illustrated with reference to and with the help of forgoing examples and accompanying drawings.
23. A method of manufacturing asymmetric flexible pneumatic actuator [AFPA] substantially as herein described and illustrated with reference to and with the help of forgoing examples and accompanying drawings.