Unit 5 includes the theoretical analysis on kinematics, dynamics and stresses involved. Therefore total length of the string = 3* L1 + 2* Lw1 + 2* L2 + 4* Lw2 + 2*L3 + Lw3 + L = 3*6 +2*39.35 + 2*6 + 4*1.855 + 2*30 +43.26 + 20 = 239.38mm Hence change in length of the string = 258.332mm 239.38mm = 18.952mm Hence the change in length of the string required for maximum movement of a finger = 18.952mm 48 5.11 - SHAPE DETERMINATION Based on the above calculations, the following few conceptual designs were put forward. The control string for each finger segment is threaded through the hollow spaces in each subsequent finger link and down through the palm itself. Pneumatic gripper A pneumatic gripper is a specific type of pneumatic actuator that typically involves either parallel or angular motion of surfaces, A.K.A tooling jaws or fingers that will grip an object. Moreover they have some gear arrangements to provide interlocking at the joints which not only decreases the load holding capacity but also increases the probability of mechanical failure at any joint. Parallel gripper A gripper mechanism is designed so that the gripper faces are parallel when the mechanism moves together and apart. True parallel jaw motion for easy tooling. Hence area = x d2/4 = 12.57 mm2 Therefore, = 233.57/12.57 = 18.58 N/mm2 Shear stress for the thumb side Shear stress = = tension force/area Tension force for the finger side = 350.35 N Area = cross sectional area of the shaft 39 Diameter of the shaft is taken as d = 4 mm.

Each finger consists of 3 links. Control inputs can also be generated from muscle activity recorded with EMG electrodes placed on a human forearm, and processed by a custom pattern recognition circuit built into the robot forearm cavity. Similarly, Shear stress on the pulley between link B and link C: = 7.435 cos(60 - /2) N/mm2 where is the angle between link B and C. Shear stress on the pulley between link C and the base: = 7.435 cos(60 - /2) N/mm2 where is the angle between link C and the base. The pulleys used have an effective diameter of 10mm and an external diameter of 15mm. ` Figure 1(b) Fingers with three links, N: frictional force. [5] Sarah Jane Wikman. INTER-FINGERCOORDINATED DC MOTOR DRIVEN GRASPING ROBOTIC HAND. The angular velocity of the link A about point P be 2.

2) Prensilia Srl The EH1 Milano Hand is a programmable anthropomorphic human-sized hand able to grasp a variety of objects and to sense them through multiple force and position sensors. Fingers are the elements that execute the grasp on objects, finger tips are directly in contact with a object. Indian Institute of Technology, Guwahati. By observing human hand postures researchers concluded that a large percentage of hand positions can be approximated by a simple grasping motion. the motion of each link in a finger is equal, 2 = 2 = 2 But 2 + 2 + 2 = 180 Hence 2 = 2 = 2 = 60 Hence from equation (4), we have, Lcos60 + X = - Lcos(120) + d + L 26 Or X=d+L Or X=L [since d is considered to be very small or tending towards zero] ..(5) Using equation (5) in equation (3), we have 1.366L + L = 120 Or 2.66L = 120 Or L = 120/2.66 Or L = 50.71 For convenience we take L = 50mm Hence from the above calculation we get length of each link in a finger to be 50mm. Flame Retardant. However, two actuators can be useful when the fingers can operate independently with a symmetric or unsymmetrical behaviour. Ronald F. Clayton They should come in contact with each other at an angle of 180. The figure below shows the design of a finger. Thus, a dimensional design of gripper mechanisms may have great influence on the maximum dimensions of the grasped object by a gripper, and on the grasping force, since the mechanism size may affect the grasp configuration and transmission characteristics.

The use of additive manufacturing for rapid prototyping takes virtual designs from computer aided design (CAD) or animation software. So less maintenance is required. For such a configuration of the grippers(figure ), the total length of the string. what kind of objects can be grasped and what kind of manipulations can be performed with a grasped object. hb`````P @16,"W1`\tPm}6Ss',Q|UZcR3:@4p The index is 5, and joint number and degree of freedom equal to the human finger joint have been established. The utility of the design and its future aspects has been included in Unit 8. 5 UNIT : 1 PROBLEM STATEMENT Research and Development Establishment (Engineers), an organisation under The Defence Research and Development Organisation, wanted us to design, analyse & develop a mechanical gripper capable of lifting objects of given load and dimensions. But as we increase the distance, decreases and hence the sine component of the force. 45 Tearing stress on the link on each thumb: Tearing stress between link A and link B Force = 2T cos(60 - /2) Or Force = 700.7 cos(60 - /2) [since T= 350.35 on the finger side] Area = thickness x length of tear = 30 x 6 = 180 mm2 t = force/area = 700.7 cos(60 - /2) / 180 = 3.9cos(60 - /2) N/mm2 Where is the angle between link A and B. Tearing stress between link B and link C t = 3.9cos(60 - /2) N/mm2 Where is the angle between link B and C. Tearing stress between link C and the base t = 3.9cos(60 - /2) N/mm2 Where is the angle between link C and the base. Shear stress for the finger side Shear stress = = tension force/area Tension force for the finger side = 233.57 N Area = cross sectional area of the shaft Diameter of the shaft is taken as d = 4 mm. Address: Copyright 2022 PDFCOFFEE.COM. This is because the same component of the tension force will be transmitted through the pulley, shaft connecting the two links and finally to the link. 30 5.4 - CALCULATION OF GRIPPING FORCE The load to be lifted by the gripper is 10kg. High gripping force to weight ratio. The Hand is driven by 20 Smart Motor units mounted below the wrist which provide compliant movements. Ethylbenzene is a single-ring alkylaromatic compound. In the manufacture of the prototype ABS is used. Hence 3 + 3 + 3 = 180 Since the two thumbs move symmetrically, 3 = 3 , 3 = 3 , 3 = 3 and also since each link moves equally, 3 + 3 + 3 = 3 + 3 + 3 = 180 or 3 = 3 , 3 = 3 , 3 = 3 = 60 putting in equation (6), we have, Lcos60 + Y + Lcos60= - Lcos(120) Lcos(180) Lcos(180) Lcos(120) Or Y = 2L Or Y = 100mm 29 Variation of X, Y and L with respect to the angles 1, 1, 1, 2, 2, 2 The above table shows the variation of X,Y and L with the variation of the angles 1, 1, 1, 2, 2, 2 for the gripper to be capable of holding a body of maximum dimension of 120mm and a minimum dimension nearly equal to zero. With this, the thread gets wounded on side pulleys and relaxed on the other. Figure 31 The three fingers and the two thumbs were fabricated and tested successfully. The fingers and the thumb move independently by five motors that are mounted on the base. This force will cause tearing of the link at the circular portion. By application of pressure of two opposite pistons the jaws move synchronously towards each other. Today, they are used for a much wider range of applications and are even used to manufacture production-quality parts in relatively small number. $^k=t-} d>s]2#FvsYXV2\`0oCgC!CC. By rotating the motor, one side pulleys rotate in one direction and the other side pulleys in the other. It can be used for gripping operation in robots which performs grabbing and releasing of hazardous materials from one place to another provided the gripper is installed with an arm. 46 5.10 - CALCULATION OF THE CHANGE IN LENGTH OF THE STRING REQUIRED FOR MAXIMUM MOVEMENT OF A FINGER Figure 21 The configuration of the finger in its ideal state is shown in the figure. Fixed point String Figure 3 Each finger stemming from the palm can be modeled as an open chain linkage system stemming from a fixed point.

11 Survey on fingered gripper 1) Shadow Robot Company Ltd. Model Smart Motor Hand (C6M) uses Shadow's electric Smart Motor actuation system, rather than the pneumatic Air Muscle actuation system of other Dextrous Hand systems. Rapid protyping is the automatic construction of physical objects using additive manufacturing technology. reports/pptsc_lg.asp.htm http://www.shadowrobot.com/reports_es.htm http://www.megabots_reports/grippers.html http://mindtrans.narod.ru/hands/pictures/openarm_v2 http://www. The basic idea about grippers and type of gripper currently available is discussed in Unit 2. 4.4 - Working Principle This gripper has five fingers with three links which will augment the friction force and will help in firmly gripping the object. Similarly, Shear stress on the shaft between link B and link C: = 37.174 cos(60 - /2) N/mm2 where is the angle between link B and C. Shear stress on the shaft between link C and the base: = 37.174 cos(60 - /2) N/mm2 where is the angle between link B and C. 43 Shear stress on the shafts connecting two links on each thumb Shear stress on the shaft between link A and link B: Force = 2T cos(60 - /2) or force = 2x 350.35 cos(60 - /2) [ since tension T for finger = 233.57N] or force = 700.7 cos(60 - /2) Area = x r2 Since radius of the pulley is 2mm Therefore, Area = 12.566 mm2 = force/area = 700.7cos(60 - /2)/ 12.566 N/mm2 = 55.76 cos(60 - /2) N/mm2 where is the angle between link A and B. Traini, DESIGN, ANALYSIS AND DEVELOPMENT OF MECHANICAL GRIPPER Submitted By SWASTIK BHATTACHARYA 200815059 SUBHANKAR DAS 200815055 TANMAY ROY 200815061 Under The Guidance Of SHRI MK PATHAK, SCIENTIST D, SHRI ANUPAM BANSAL, SCIENTIST B, Research & Development Establishment (Engineers), Pune For Summer Training, May June, 2011 Department Of Mechanical Engineering Sikkim Manipal Institute Of Technology Majitar, East Sikkim 737136 Under SIKKIM MANIPAL UNIVERSITY 1 Contents Page No I) Certificate 3 II) Acknowledgement 4 II) Abstract 5 Unit 1 Problem statement 6 Unit 2 Introduction 7 Unit 3 Literature & survey 10 Unit 4 Concept 17 Unit 5 Design 24 Unit 6 Prototype development 56 Unit 7 Conclusion 60 Unit - 8 Utility, Limitations, Future Aspects 61 Unit 9 Bibliography 64 2 3 Acknowledgement We would like to thank Shri MK Pathak, Scientist D and Shri Anupam Bansal, Scientist B, Research & Development Establishment (Engineers), Pune for guiding us throughout the project especially with the design calculations and analysis. These peculiarities can be considered well known when it is taken into account the great variety of mechanisms which have been used. For non synchronizing motion of five fingers, five actuators has been used to grip the object. The tangential velocity of the link A about point P be V2. 2) Pitch, Yaw and roll movement can be given to the gripper to enhance its degree of freedom. It should be easily fabricated with easily available resources. The radial component of the 2 forces adds up. Such a robot system which is designed to support humans in non-specialized, nonindustrial surroundings like these must, among many other things, be able to grasp objects of different size, shape and weight. Hence load on each side = 98.1/2 N = 49.05 N The coefficient of friction between the rubber and metal block is 0.7. They are controlled through a computer interface which takes TTL level inputs representing commands for finger contraction and extension, and converts them to drive signals for each motor.

12 3. 23 UNIT: 5 DESIGN 5.1 - CALCULATION OF THE LENGTH OF EACH LINK IN A FINGER Figure 8 Let Distance between the shaft of the finger and the edge of the thumb be X, Distance between the shafts of the thumb be Y, Length of each link be L. Maximum dimension of the body to be held by the gripper between the finger and the thumb be D = 120 mm Minimum dimension of the body to be held by the gripper be d 24 Let us consider the configuration of the gripper for holding the body of maximum dimension. FINGER SIDE The torque on the motor driving the fingers is Torque = T x radius of the pulley Since radius of the pulley used is 5 mm Tension (T) = 233.57 N Hence Torque = 233.57 x 5 = 1167.85 Nmm = 1.1675 Nm THUMB SIDE The torque on the motor driving the thumbs is Torque = T x radius of the pulley Since the radius of the pulley used is 5 mm Tension (T) = 350.35 N Hence Torque = 350.35 x 5 = 1751.75 Nmm = 1.7517 Nm 35 5.8 - KINEMATIC ANALYSIS Now we shall analyse the motion a finger considering it as a 4 bar open chain mechanism. 19 4.3 - String and Pulley Driven Actuation The control method for this robotic hand uses strings fixed at each joint which are connected to a motor placed inside the palm. The synchronized, true parallel motion of the fingers is generated by a pinion mechanism powered by a double acting piston. endstream endobj startxref They are shown in the figures below:- Figure 22 49 Figure 23 50 Figure 24 Among the above mentioned conceptual designs, the concept 2 (figure 23) was chosen due to its better resemblance with the human arm and its capability of holding irregular bodies being better than the others. The problem statement is discussed in Unit 1. The same robotic hand has been used as a prosthetic device. The forearm, which measures 4 inches in diameter at its base and is approximately 8 inches long, houses all 14 motors, 12 separate circuit boards, and all of the wiring for the hand. Dimensional Stability 56 The following assembly was required to be fabricated.

Sitemap 22