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The development of soft gripper for the versatile robot hand
Mechanism and IVlechine Theory, 1978.Vol. 13, pp. 351-359. PergamonPress. Printed in Great Britain
The Development of Soft Gripper for the Versatile Robot Hand Shigeo Hiroset and YoJi Umetenit
Received for publication 24 October 1977 AbItract This paper deals with a new type of soft gripper which can softly and gently conform to objects of any shape and hold them with uniform pressure. This gripping function is realized by means of a mechanism consisting of multi-links and series of pulleys which can be simply actuated by a pair of wires. The possibilities of this gripper are demonstrated by a pair of mechanical model. Introduction IN THE present state of industrial robot technology, any significant advancement with regard to versatility will result from an improvement of its gripping mechanisms. If the hand could manipulate hard, fragile or soft objects of various shapes, the industrial robot could be utilized in wider fields, such as agriculture, medical treatment or on the automatic assembly line. The necessity for a versatile robot hand has become apparent in recent years, and several types of gripper have already been proposed (e.g. a mechanism using moulding technology by Lundstrom [1], a three fingered multiple prehension hand by Skinner[2] etc.). This paper deals with a singular type of gripping mechanism which has relatively simple control mechanisms and can softly and gently conform to objects of any shape and hold them with uniform pressure. The universal gripper proposed in this paper is here in after referred to as the "softgripper". The authors have been making a systematic study of the "Active Cord Mechanism" (a machine having a linearly slender configuration and making an active and flexible sinuous motion by means of groups of actuators and sensors installed along the trunk). The study of this mechanism (i.e. the ACM) was originally inspired by observations of the miscellaneous movements of the snake. The subsequent biomechanical study of the snake, and experiments with the fabricated ACM mechanical model shown in Fig. 2 clarified kinematical relations and the controlling principles of the ACM[3, 4]. The soft gripper dealt with in this paper applies such kinematic and controlling principles and realized these principles by means of a newly designed mechanism consisting of multi-links and series of pulleys actuated by a pair of wires. The Kinematics of Soft Gripping Action The soft gripping action described in this paper involves the following two functions; (1) the finger can actively conform to the periphery of objects of any shape, i.e. including concave ones, and (2) the finger can produce uniform pressure after having gripped the object. As for the former function (1), a suitable mechanism for it will be discussed later in this paper. The latter function (2) will now be explained by applying the kinematic relations of the ACM. +Departmentof PhysicalEngineering,TokyoInstituteof Technology,2-12-10hokayama,Meguro-ku,Tokyo,Japan. 351
352
(a)
(b)
(c)
Figure 1.
Figure 2.
Rgure 1. Schematic explanation of the ideal soft gripping movement. Figure 2. Gripping movement by the previously constructed Active Cord Mechanism [4]. It has already been derived that the normal force density function/,(s), which expresses the normal component of the force induced by the bending moment T(s) at the unit length of the ACM longitudinal axis s, is expressed as follows d2T(s)
/o(s)=~.
(l)
It should be noted that this relationship is derived under the assumption that the ACM consists of infinitely small segments and has no abrupt bending along the trunk. We also assume that the soft gripper discussed here makes a continuous bending movement, as does an octopus' tentacle or an elephant's trunk. Under these conditions eqn (1) holds good for the gripping action. The modification necessary to adapt the above equation for a soft gripper consisting of finite segments will be discussed in the following section. First of all let us evaluate the torque distribution. When a typical soft gripping condition, i.e. uniform gripping pressure along the finger, f,(s) -=/= const, is assumed and the coordinate of s is defined along the finger as shown in Fig. l(c), the following condition should be satisfied dT(/)_ 0, ds
T(l) = 0.
(2)
Equations (1) and (2) yields the following torque distribution T(s)
where
/2 To ~- ~-f. Z--
(4)
353 It is thus deduced that a uniform gripping pressure =along the finger can be obtained when the finger actively produces the bending moment distribution as in eqn (3). The physical meaning of this relationship can be easily understood from an analogy with the theory of the strength of materials. Consider a cantilever beam loaded along its length as shown in Fig. 3. In this case the relation between the bending moment M(s) and the load w(s) is expressed as d2M(s)
= - w(s).
(5)
In the case of uniform load, w(s) ----w = const., the bending moment diagram, BMD, is of the parabola shape as shown in Fig. 3. This BMD corresponds to eqn (3) where torque distribution T(s) has virtually the same meaning as the bending moment of M(s). We should thereby say that the kinematics of the soft gripper expressed the external forces induced by the inner actuated moment whereas the theory of the strength of materials deals with the internal bending moment produced by the external load. Thus eqn (1) of the gripping action can be said to express the opposite causality of eqn (5). By adapting these relations, any type of grip moment distribution and gripping pressure could be estimated from the corresponding bending moment acting on the beam of the same shape. $
IIIII!il
l~#'SfJ'~J'J"~J'~j'ffLI~fj"~JJ~jlffffj~
SFD
BMD
Rgure 3. The resultant shearing force SFD and bending moment BMD of a distributed load acting along a cantilever beam.
Design of the Soft Gripper (1) The mechanism of the soft gripper To acquire a suitable torque distribution along the finger, several types of the mechanism could be conceived. As shown in Fig. 2 the ACM mechanical model has already realized the soft gripping actions. The ACM mechanical model consists of 20 articulation units, and each unit has servomechanisms which individually produce bending movements in response to the automatically operated controls. The ACM has 40 tactile sensors on both sides of its trunk, and it can detect mechanical contact with an object and actively conform to its shape. The ACM model is about 2 m in length, 14 cm in width and weighs about 14 kg. This ACM has the intrinsic ability to carry out miscellaneous functions besides its gripping movement. But if we only pursue the function of gripping, this mechanism is too complicated and cannot be adapted
354
directly. The authors have, therefore, investigated some more simplified mechanisms and finally developed the following mechanism. The segmental mechanism is schematically illustrated in Fig. 4. The adjacent links and pulleys are connected with a spindle and are free to rotate around it. This mechanism is actuated by a pair of wires, one being a "grip wire" which produces the gripping movement and the other a "release wire" which pulls antagonistically and produces the release movement from the gripping position. These two wires pass from the base to the tip of the fingers as shown in Fig. 8. It is notable that in this mechanism each of the segments are not individually actuated; instead all the segments are actuated with only the traction of a pair of wires. The whole mechanism of the finger and the driving unit is thus constructed quite simply. The pulleys for the grip wire are designed to follow the principle expressed in the eqn (3). This point will be treated in detail later. All the pulleys for the release wire are of the same diameter and thus produce a uniform reverse bending moment along the trunk. The antagonistic torque distributions along the finger are shown in Fig. 5. The sequence of the gripping action is as follows. Let us first presume that the finger is in the state of Fig. l(a). In this position the release wire is pulled and the grip wire is loosened. When the grip wire is pulled, the grip torque of the whole finger increases and incidentally, as the pulley series are designed to follow the eqn (3), the grip torque conveniently exceeds the antagonistic release torque from the base. Thus the finger makes a bending moment from the base segment. As the grip wire is gradually pulled, the point x in Fig. 5 traverses from the base segment to the tip segment, and finally all the segments produce grip moment. During this process of wire traction, the disposition of each gripper's links are determined by the mechanical contact with an object. When the link i makes contact with an object and further movement is hindered the next link i + 1 begins to rotate toward the object until it makes
Proximal Grip wire
~
Releasewire ~
~)~ L" _~
Figure 4. Segmental mechanism of the soft gripper.
/Grip Release (Reverse direction)
0
n
Number of links
Rgure S. Torque distribution along the finger caused by the grip and release wire traction.
355 contact and thus it follows the peripheral shape of the object. Hence, it might be said that the pulleys of this mechanism play two roles, one in driving the distal part of the finger and bending it at point x as in Fig. 5 and the other in rotating freely around the spindle and conveying the tension of the wire's tractive forces after the links have conformed to the object. The release movement begins only to increase the tractive force of the release wire and loosen the grip wire. Then point x of Fig. 5 returns from the tip segment to the base and forms the coiled starting form again. (2) The design of the pulley series As discussed in the previous section both the functions of conforming and uniform gripping of the soft gripper are induced from a deliberately designed pulley series. In this section the method of design will be shown. Presuming the nomenclature of the links and the joints to be as shown in Fig. 6, the torque series Ti of each of the joints are derived from the modification of the eqn (3) in the discrete form as (6)
Ti = Lif
where Li is defined as I._,. l,_p
Li -=/oP=O
i=0-n-1
(7)
i=n
and f is the uniformly produced gripping pressure. When the length of all the links are equal li -- l -- const., eqn (6) is expressed more simply as T/= To(l - / ) ( 1 - t--~+ n 1)
(8)
where, To =- n(n
+
2
1)12f.
(9)
For example, one of the torque progressions of the joints from J0 to Jlo is calculated as 55, 45, 36, 28, 21, 15, 10, 6, 3, 1, and O. Where the 0th joint is the tip of the finger and thereby produces no torque. In the case of the simple pulley mechanism shown in Fig. 7(a), the diameters of the pulley
Figure 6. Nomenclature of the links and joints.
(a)
Rgure 7. Two types of wire pulley mechanisms for the soft gripper.
356
are distinctly designed. The wire is pulled with the same tensile force all along the finger as the friction of the puiley's rotation is negligible, required torque distribution is obtained with the pulleys diameters being proportionally designed according to eqn (6). Thus the ith radius of the pulley Ri is expressed as L i ei = ~6Ro.
(10)
When the condition of li = ! = const, is given, the R~ is expressed as
The single pulley series is simple in its mechanism but the same function can also be obtained by the double pulley series shown in Fig, 7(b) and sometimes this mechanism is more feasible from a manufacturing standpoint. In the case of the double pulley series the ratio of the ith pulley's radius K~ between the large and small pulleys Ri and ri is derived as Ko
l
(12)
Ri-z L i Ki =
Ri
L i-I
i
= l - n.
The condition of l~ -- l -- const, is given, the ratio Ki is expressed as K0=I,
Ki--
n-i n-i+2"
(13)
In the case of a gripper consisting of 10 links, the ratio of the radius Ki (i = 0 - 10) is calculated as
1,
9 8 7654321 and 0. 11' 10' 9' 8' 7 ' 6 ' 5' 4' 3'
The gripping force f is derived from the eqn (6) as Ro f = ~-~Po
(14)
where, Ro is the radius of the 0th pulley, and Po is the tractive force of the grip wire from the base segment. For example, a soft gripper consisting of 10 links, each 3 cm in length and having Releose
,,,!
.....
Grip w~re
Grip
Figure 8. Total mechanism of the soft gripper.
357
a 0th pulley Ro = 1 cm in radius produces the gripping pressure [ -- 20 g/cm when the wire is pulled with the force Po-- 10 kg.
Experiment To verify the soft gripping function with the mechanism mentioned above, a pair of soft grippers consisting of 10 links was constructed as shown in Fig. 8. The length of each link is 3 cm. The radius of the base (0th) segment is 1 cm. Figure 9(a)--(c) shows the sequence of the gripping action. From the photographs it is obvious that the soft gripper can conform to objects of concave shape. As shown in Fig. 10 the soft gripper can also grip an object comparatively
Ca)
Cb)
(d
Figure 9.
Serial photos of gripping motion.
358
Figure 10. The soft gripper conformed to a comparatively small object.
Figure 11. Traces left on the clay indicating the uniform pressure along the gripper.
smaller than the finger. As the wires are operated manually in this model, the time required for a complete gripping and releasing cycle can be varied to the extent to less than 1 sec. As to the uniformity of the gripping pressure, it is directly felt when a part of our body is embraced by the soft gripper. It is, however, more quantitatively measured by the grasping of plastic materials, e.g. clay. As the inner part of the soft gripper has pyramidal shaped projections, square shaped traces are left on the surface of the clay when it gripped by the soft gripper. Measurements showed that the area of the traced squares were almost the same in every part of the finger (as shown in Fig. ll) and thus proved the uniformity of the gripping pressure.
Conclusion end Future Application In this paper, the principles and mechanism of a new type of gripping mechanism, which the authors have named the soft gripper, were discussed. The soft gripper has the following characteristics. (1) It can conform to objects of almost any shape and size. (2) It can grip an object with uniform pressure along the whole finger. (3) It has a relatively simple mechanism and can be controlled with only the traction of a pair of wires. Because of the simplicity of this mechanism and its peculiar functions the soft gripper can be applied in various fields in the future. For instance, as the versatile hands of an industrial robot, it could promote the efficiency of its tasks and articles such as glassware could be easily manipulated. Because of the softness of the gripping movement the soft gripper could also be utilized in the agricultural fields, e.g. machines to harvest fruit or handle eggs. Moreover. it could be used as an instrument capture alive wild animals such as lions, snakes and fish. In the medical fields this gripper could take the part of a nurse and could transport a patient from bed to bed or support the patient during medical treatment.
359
Roforon©o| I. G. Lundstrom, A new method of designingIp']ppers.6th Int.Syrap. IndlRobots. Nottingham, England (1976). 2. F. Skinner,Multipleprehensionhands for assembly robots.5tk Int.Syrup.IndlRobots. Chicago (1975). 3. Y. Umetani and S. Hirose, Biomochenic~d study of serpentine locomotion. Proc. Romansy Syrnp. Udine, Italy. Springer-Verlq,Berlin(1973). 4. Y. Umetani and S. Hirose, Biomechanical study of active cord mechanism with tactile sensors. 6th Int. Symp. lnd! Robots. England (1976).
The Development of Soft Gripper for the Versatile Robot Hand Shigeo Hiroset and YoJi Umetenit
Received for publication 24 October 1977 AbItract This paper deals with a new type of soft gripper which can softly and gently conform to objects of any shape and hold them with uniform pressure. This gripping function is realized by means of a mechanism consisting of multi-links and series of pulleys which can be simply actuated by a pair of wires. The possibilities of this gripper are demonstrated by a pair of mechanical model. Introduction IN THE present state of industrial robot technology, any significant advancement with regard to versatility will result from an improvement of its gripping mechanisms. If the hand could manipulate hard, fragile or soft objects of various shapes, the industrial robot could be utilized in wider fields, such as agriculture, medical treatment or on the automatic assembly line. The necessity for a versatile robot hand has become apparent in recent years, and several types of gripper have already been proposed (e.g. a mechanism using moulding technology by Lundstrom [1], a three fingered multiple prehension hand by Skinner[2] etc.). This paper deals with a singular type of gripping mechanism which has relatively simple control mechanisms and can softly and gently conform to objects of any shape and hold them with uniform pressure. The universal gripper proposed in this paper is here in after referred to as the "softgripper". The authors have been making a systematic study of the "Active Cord Mechanism" (a machine having a linearly slender configuration and making an active and flexible sinuous motion by means of groups of actuators and sensors installed along the trunk). The study of this mechanism (i.e. the ACM) was originally inspired by observations of the miscellaneous movements of the snake. The subsequent biomechanical study of the snake, and experiments with the fabricated ACM mechanical model shown in Fig. 2 clarified kinematical relations and the controlling principles of the ACM[3, 4]. The soft gripper dealt with in this paper applies such kinematic and controlling principles and realized these principles by means of a newly designed mechanism consisting of multi-links and series of pulleys actuated by a pair of wires. The Kinematics of Soft Gripping Action The soft gripping action described in this paper involves the following two functions; (1) the finger can actively conform to the periphery of objects of any shape, i.e. including concave ones, and (2) the finger can produce uniform pressure after having gripped the object. As for the former function (1), a suitable mechanism for it will be discussed later in this paper. The latter function (2) will now be explained by applying the kinematic relations of the ACM. +Departmentof PhysicalEngineering,TokyoInstituteof Technology,2-12-10hokayama,Meguro-ku,Tokyo,Japan. 351
352
(a)
(b)
(c)
Figure 1.
Figure 2.
Rgure 1. Schematic explanation of the ideal soft gripping movement. Figure 2. Gripping movement by the previously constructed Active Cord Mechanism [4]. It has already been derived that the normal force density function/,(s), which expresses the normal component of the force induced by the bending moment T(s) at the unit length of the ACM longitudinal axis s, is expressed as follows d2T(s)
/o(s)=~.
(l)
It should be noted that this relationship is derived under the assumption that the ACM consists of infinitely small segments and has no abrupt bending along the trunk. We also assume that the soft gripper discussed here makes a continuous bending movement, as does an octopus' tentacle or an elephant's trunk. Under these conditions eqn (1) holds good for the gripping action. The modification necessary to adapt the above equation for a soft gripper consisting of finite segments will be discussed in the following section. First of all let us evaluate the torque distribution. When a typical soft gripping condition, i.e. uniform gripping pressure along the finger, f,(s) -=/= const, is assumed and the coordinate of s is defined along the finger as shown in Fig. l(c), the following condition should be satisfied dT(/)_ 0, ds
T(l) = 0.
(2)
Equations (1) and (2) yields the following torque distribution T(s)
where
/2 To ~- ~-f. Z--
(4)
353 It is thus deduced that a uniform gripping pressure =along the finger can be obtained when the finger actively produces the bending moment distribution as in eqn (3). The physical meaning of this relationship can be easily understood from an analogy with the theory of the strength of materials. Consider a cantilever beam loaded along its length as shown in Fig. 3. In this case the relation between the bending moment M(s) and the load w(s) is expressed as d2M(s)
= - w(s).
(5)
In the case of uniform load, w(s) ----w = const., the bending moment diagram, BMD, is of the parabola shape as shown in Fig. 3. This BMD corresponds to eqn (3) where torque distribution T(s) has virtually the same meaning as the bending moment of M(s). We should thereby say that the kinematics of the soft gripper expressed the external forces induced by the inner actuated moment whereas the theory of the strength of materials deals with the internal bending moment produced by the external load. Thus eqn (1) of the gripping action can be said to express the opposite causality of eqn (5). By adapting these relations, any type of grip moment distribution and gripping pressure could be estimated from the corresponding bending moment acting on the beam of the same shape. $
IIIII!il
l~#'SfJ'~J'J"~J'~j'ffLI~fj"~JJ~jlffffj~
SFD
BMD
Rgure 3. The resultant shearing force SFD and bending moment BMD of a distributed load acting along a cantilever beam.
Design of the Soft Gripper (1) The mechanism of the soft gripper To acquire a suitable torque distribution along the finger, several types of the mechanism could be conceived. As shown in Fig. 2 the ACM mechanical model has already realized the soft gripping actions. The ACM mechanical model consists of 20 articulation units, and each unit has servomechanisms which individually produce bending movements in response to the automatically operated controls. The ACM has 40 tactile sensors on both sides of its trunk, and it can detect mechanical contact with an object and actively conform to its shape. The ACM model is about 2 m in length, 14 cm in width and weighs about 14 kg. This ACM has the intrinsic ability to carry out miscellaneous functions besides its gripping movement. But if we only pursue the function of gripping, this mechanism is too complicated and cannot be adapted
354
directly. The authors have, therefore, investigated some more simplified mechanisms and finally developed the following mechanism. The segmental mechanism is schematically illustrated in Fig. 4. The adjacent links and pulleys are connected with a spindle and are free to rotate around it. This mechanism is actuated by a pair of wires, one being a "grip wire" which produces the gripping movement and the other a "release wire" which pulls antagonistically and produces the release movement from the gripping position. These two wires pass from the base to the tip of the fingers as shown in Fig. 8. It is notable that in this mechanism each of the segments are not individually actuated; instead all the segments are actuated with only the traction of a pair of wires. The whole mechanism of the finger and the driving unit is thus constructed quite simply. The pulleys for the grip wire are designed to follow the principle expressed in the eqn (3). This point will be treated in detail later. All the pulleys for the release wire are of the same diameter and thus produce a uniform reverse bending moment along the trunk. The antagonistic torque distributions along the finger are shown in Fig. 5. The sequence of the gripping action is as follows. Let us first presume that the finger is in the state of Fig. l(a). In this position the release wire is pulled and the grip wire is loosened. When the grip wire is pulled, the grip torque of the whole finger increases and incidentally, as the pulley series are designed to follow the eqn (3), the grip torque conveniently exceeds the antagonistic release torque from the base. Thus the finger makes a bending moment from the base segment. As the grip wire is gradually pulled, the point x in Fig. 5 traverses from the base segment to the tip segment, and finally all the segments produce grip moment. During this process of wire traction, the disposition of each gripper's links are determined by the mechanical contact with an object. When the link i makes contact with an object and further movement is hindered the next link i + 1 begins to rotate toward the object until it makes
Proximal Grip wire
~
Releasewire ~
~)~ L" _~
Figure 4. Segmental mechanism of the soft gripper.
/Grip Release (Reverse direction)
0
n
Number of links
Rgure S. Torque distribution along the finger caused by the grip and release wire traction.
355 contact and thus it follows the peripheral shape of the object. Hence, it might be said that the pulleys of this mechanism play two roles, one in driving the distal part of the finger and bending it at point x as in Fig. 5 and the other in rotating freely around the spindle and conveying the tension of the wire's tractive forces after the links have conformed to the object. The release movement begins only to increase the tractive force of the release wire and loosen the grip wire. Then point x of Fig. 5 returns from the tip segment to the base and forms the coiled starting form again. (2) The design of the pulley series As discussed in the previous section both the functions of conforming and uniform gripping of the soft gripper are induced from a deliberately designed pulley series. In this section the method of design will be shown. Presuming the nomenclature of the links and the joints to be as shown in Fig. 6, the torque series Ti of each of the joints are derived from the modification of the eqn (3) in the discrete form as (6)
Ti = Lif
where Li is defined as I._,. l,_p
Li -=/oP=O
i=0-n-1
(7)
i=n
and f is the uniformly produced gripping pressure. When the length of all the links are equal li -- l -- const., eqn (6) is expressed more simply as T/= To(l - / ) ( 1 - t--~+ n 1)
(8)
where, To =- n(n
+
2
1)12f.
(9)
For example, one of the torque progressions of the joints from J0 to Jlo is calculated as 55, 45, 36, 28, 21, 15, 10, 6, 3, 1, and O. Where the 0th joint is the tip of the finger and thereby produces no torque. In the case of the simple pulley mechanism shown in Fig. 7(a), the diameters of the pulley
Figure 6. Nomenclature of the links and joints.
(a)
Rgure 7. Two types of wire pulley mechanisms for the soft gripper.
356
are distinctly designed. The wire is pulled with the same tensile force all along the finger as the friction of the puiley's rotation is negligible, required torque distribution is obtained with the pulleys diameters being proportionally designed according to eqn (6). Thus the ith radius of the pulley Ri is expressed as L i ei = ~6Ro.
(10)
When the condition of li = ! = const, is given, the R~ is expressed as
The single pulley series is simple in its mechanism but the same function can also be obtained by the double pulley series shown in Fig, 7(b) and sometimes this mechanism is more feasible from a manufacturing standpoint. In the case of the double pulley series the ratio of the ith pulley's radius K~ between the large and small pulleys Ri and ri is derived as Ko
l
(12)
Ri-z L i Ki =
Ri
L i-I
i
= l - n.
The condition of l~ -- l -- const, is given, the ratio Ki is expressed as K0=I,
Ki--
n-i n-i+2"
(13)
In the case of a gripper consisting of 10 links, the ratio of the radius Ki (i = 0 - 10) is calculated as
1,
9 8 7654321 and 0. 11' 10' 9' 8' 7 ' 6 ' 5' 4' 3'
The gripping force f is derived from the eqn (6) as Ro f = ~-~Po
(14)
where, Ro is the radius of the 0th pulley, and Po is the tractive force of the grip wire from the base segment. For example, a soft gripper consisting of 10 links, each 3 cm in length and having Releose
,,,!
.....
Grip w~re
Grip
Figure 8. Total mechanism of the soft gripper.
357
a 0th pulley Ro = 1 cm in radius produces the gripping pressure [ -- 20 g/cm when the wire is pulled with the force Po-- 10 kg.
Experiment To verify the soft gripping function with the mechanism mentioned above, a pair of soft grippers consisting of 10 links was constructed as shown in Fig. 8. The length of each link is 3 cm. The radius of the base (0th) segment is 1 cm. Figure 9(a)--(c) shows the sequence of the gripping action. From the photographs it is obvious that the soft gripper can conform to objects of concave shape. As shown in Fig. 10 the soft gripper can also grip an object comparatively
Ca)
Cb)
(d
Figure 9.
Serial photos of gripping motion.
358
Figure 10. The soft gripper conformed to a comparatively small object.
Figure 11. Traces left on the clay indicating the uniform pressure along the gripper.
smaller than the finger. As the wires are operated manually in this model, the time required for a complete gripping and releasing cycle can be varied to the extent to less than 1 sec. As to the uniformity of the gripping pressure, it is directly felt when a part of our body is embraced by the soft gripper. It is, however, more quantitatively measured by the grasping of plastic materials, e.g. clay. As the inner part of the soft gripper has pyramidal shaped projections, square shaped traces are left on the surface of the clay when it gripped by the soft gripper. Measurements showed that the area of the traced squares were almost the same in every part of the finger (as shown in Fig. ll) and thus proved the uniformity of the gripping pressure.
Conclusion end Future Application In this paper, the principles and mechanism of a new type of gripping mechanism, which the authors have named the soft gripper, were discussed. The soft gripper has the following characteristics. (1) It can conform to objects of almost any shape and size. (2) It can grip an object with uniform pressure along the whole finger. (3) It has a relatively simple mechanism and can be controlled with only the traction of a pair of wires. Because of the simplicity of this mechanism and its peculiar functions the soft gripper can be applied in various fields in the future. For instance, as the versatile hands of an industrial robot, it could promote the efficiency of its tasks and articles such as glassware could be easily manipulated. Because of the softness of the gripping movement the soft gripper could also be utilized in the agricultural fields, e.g. machines to harvest fruit or handle eggs. Moreover. it could be used as an instrument capture alive wild animals such as lions, snakes and fish. In the medical fields this gripper could take the part of a nurse and could transport a patient from bed to bed or support the patient during medical treatment.
359
Roforon©o| I. G. Lundstrom, A new method of designingIp']ppers.6th Int.Syrap. IndlRobots. Nottingham, England (1976). 2. F. Skinner,Multipleprehensionhands for assembly robots.5tk Int.Syrup.IndlRobots. Chicago (1975). 3. Y. Umetani and S. Hirose, Biomochenic~d study of serpentine locomotion. Proc. Romansy Syrnp. Udine, Italy. Springer-Verlq,Berlin(1973). 4. Y. Umetani and S. Hirose, Biomechanical study of active cord mechanism with tactile sensors. 6th Int. Symp. lnd! Robots. England (1976).