EP0233386A1

EP0233386A1 - A lifting clamp

Info

Publication number: EP0233386A1
Application number: EP86300151A
Authority: EP
Inventors: Hatsuo Tsuyama
Original assignee: Eagle Clamp Co Ltd
Current assignee: Eagle Clamp Co Ltd
Priority date: 1986-01-13
Filing date: 1986-01-13
Publication date: 1987-08-26
Also published as: DE3669868D1; EP0233386B1

Abstract

AA lifting clamp comprising a body member (10) having a pair of leg portions (11) defining therebetween a slot(s) for receiving an element to be lifted, jaw means comprising a first jaw (30) on one leg and a second jaw (50) on the other leg, the jaws being relatively adjustable on the body for gripping the element between the jaws, the second jaw being adjustable along a guide (61a) provided on the body and extending towards the mouth of the slot at an acute angle to the slot, a lifting member (20) movably mounted on the body and link means (41,42) connected between the lifting member and the jaw means (30,50) whereby the lifting member relatively urges the jaws towards each other so that lifting force is translated to gripping force, characterised by detention means (80) for securing the second jaw to the body in selected adjustment positions, the second jaw and the body having formations (81a,81b) which permit adjustment of the second jaw along the guide until a gripping force is exerted, the arrangement being such that the reaction to the gripping force urges the formations into engagement to prevent reverse movement of the second jaw.

Description

The present invention relates to a lifting clamp, and more particularly relates to an improvement of slot-width adjusting mechanism in a lifting clamp of the type having a wedge which is slidably guided on a guiding plane inclining to the median plane of the slot of the clamp at an acute angle convexed toward the opening of the slot.
In a clamp for lifting heavy materials in the prior art, it was common to provide ridged or roughened gripping surfaces for gripping jaws in order to prevent the material gripped therebetween from slipping out of the clamp. However, the ridged or roughened gripping surfaces tend to damage the materials at the gripped surfaces. This damage is not confined to the surface of the material but also reaches to its interior structure or texture of the material and causes the deterioration of the strength of the material. Therefore, it has been demanded for clamps which does not damage the material to be lifted. Provision of ridged or roughened gripping surfaces aims to avoid the slipping out accident, thus the demand for clamps which do not damage the materials to be lifted contradicts to the demand for safety clamp which may avoid the slipping out accident.
Also it was common to provide a clamp with a slot-width adjustment mechanism for enabling the clamp to be utilized for lifting a variety of materials which have different thickness at the portion to be gripped.
It has been known a clamp having a slot-width adjustment mechanism of the type as shown in the Reference Drawing attached herewith. With reference to the drawing, a clamp having a pair of leg portions defining a slot for receiving a material to be lifted is shown. Disposed on one of leg portions 1 is a guide plate 2 having a guide surface 2a which inclines to median plane M of slot S at an acute angle 6 convexed toward the opening of the slot. A wedge S having a flat gripping surface 3a is slidably guided on guiding surface 2a. Driving means for driving the wedge to-and-fro along the guiding surface comprises a screw rod 4, one end of which is screwed through a threaded sleeve 3a which in turn pivoted on a pair of pins secured to wedge 3, and the other end of which is slidably supported on a sleeve 5 which in turn pivoted on a pair of pins secured to bell crank arm 6. Screw rod 4 is provided with a pair of escutchionr 5a and 5b on opposite side of sleeve 5 with predetermined play. A coil spring 7 is disposed between escutchion 5a and sleeve 5 to urge the screw rod toward wedge 3. Bell crank arm 6 is pivoted on a pin 8 secured to the body. Shackle 9 is pivoted on a pin secured to bell crank arm 6 for linking the wedge to the shackle.
There has been found some problems in the slot-width adjusting mechanism of the type shown in the Reference Drawing (hereinafter referred to as wedge type clamp).
One is, wedge 3 tends to be moved back along the guiding surface when a gripping force is applied to gripping surface 3a. This problem is caused on the fact that when gripping force A is applied to surface 3a, reaction force having a component B in the opposite direction and a component C in the upward direction is produced on rear surface of wedge 3. As a heavier material is to be lifted, a greater gripping force is required, and thus the greater reaction component C is produced. Therefore, even if the wedge is sufficiently pressed against the material before lifting operation, the wedge tend to be moved back from the slot during the lifting operation. Vibrations and /or shocks during the lifting operation increase the tendency of this moving back. As the length of the backward movement of the wedge becomes closer to the maximum travel of the opposing movable jaw, probability of slipping out becomes larger.
It is apparent that the reaction component C can be minimised when the inclination angle e is minimised. However, when the incli- natin angle is minimised, longer travel distance in vertical direction of the wedge is required for obtaining a predetermined lateral travel distance for adjusting slot width. This requires a longer leg portion which in turn entails a problem of increase of the empty weight of the clamp. It is desirable to ristrict the backward movement of the wedge within a tolerable distance without decreasing the inclination angle.
Another problem in the wedge type clamp resides in the driving means for driving the wedge along the guiding surface to-and-fro. In one of typical driving mechanism, a threaded rod is utilized for driving the wedge as shown in the Reference Drawing. However, this requires too much time to drive the wedge. Therefore it is desirable to provide a slot-width adjusting mechanism which can be quickly operated. In another type driving mechanism, wedge is urged with a spring toward the advancing direction, and wedge is retractable by a lever linked with the wedge via cam engagement. Howevere, in the mechanism of this type, urgung force of the spring becomes weaker as the wedge is advanced into the slot. Furthermore, when the empty weight of the clamp is considerably heavy, and the clamp is used in the attitude wherein the slot is lateraly directed and the wedge is located above the slot, the wedge is readily moved back against the urging force of the spring by mens of the empty weight of the clamp. Therefore it is desirable to provide a slot-width adjusting mechanism which is operable in a clamp having a considerably heavy empty weight, and which may advance the wedge with substantially a constant urging force.
It is an object of the present invention to provide a clamp having an improved slot-width adjustment mechanism which may avoid or minimise moving back distance of wedge.
It is another object of the present invention to provide an improved slot-width adjusting mechanism which is quickly operable for adjustment.
It is a further object of the present invention to provide an improvemed slot-width adjustment mechanism which may applicable for a clamp having a considerably heavy empty weight.
The present invention relates generally to a clamp which comprises a body member having a pair of leg portions defining therebetween a slot for receiving a material to be lifted, a shackle for attachment to a lifting cable and movable to the body, a first jaw disposed on one of leg portions, link means for operatively linking the shackle to the first jaw, and a slot-width adjusting mechanism which comprises a second jaw disposed on the other leg portion and movable relative to the body with keeping its flat gripping surface parllel to the median plane of the slot. More particularly, the present invention relates to a slot-width adjusting mechanism comprising a second jaw having a gripping surface, guide means comprising first means fixed to the body for defining a guide plane inclined to the median plane of the slot at an acute angle convexed toward the opening of the slot and second means fixed to the second jaw for defining a guided plane adapted cooperatively to engage with the first means for guiding the second jaw along the guide plane, driving means for driving the second jaw to-and-fro with respect to the body along the guide plane, and detention means for preventing the second jaw from moving back in operation.
In accordance with the present invention, guide means comprises first means fixed to the body for defining a guiding plane inclined to the median piane of the slot at an acute angle convexed toward the opening of the slot, and second means fixed to the second jaw for defining a guided plane adapted cooporatively to engage with the first means for guiding the second jaw along the guide plane all of which are found in the prior art slot-width adjusting mechanism. In the present invention, however, the guide means is provided with predetermined play for allowing the second means to be disengaged from the first means and for allowing selective operation of the detention means which will be described in detail hereinafter. For the first means defining a guide plane and for the second means defining a guided plane, a variety kinds of kp_Mn structures can be utilized. Also a variety kinds of known structures can be utilized for giving a predetermined play for allowing the second means to be disengaged from the first means.
The detention means in accordance with the present invention, comprises a first series of ridges disposed fixedly to the body along a plane substantially parallel to the guide plane and a second series of ridges disposed fixedly to the second jaw along a plane l _ti_ally parallel to the guide plane and adapted selectively to mate with the first series of ridges for prohibiting relative movement of the body and the second jaw. Each of the ridges is defined with a first surface which extends in a plane parallel to the median plane or inc'ined thereto at an acute angle convexed toward the bottom of the slot less than 5° and a second surface which extends in a plane perpendicular to the median plane or inclined thereto at an acute angle toward the opening of the slot less than 90° . The limitations to the angles referred in the above are not critical, but when the inclination of the first surface exceeds 5° , disengagement of the first and second series of ridges cannot be smoothly made when re.cilient means are not provided and the the backward movement of the s.econd jaw becomes larger. Said first series of ridges can be disposed on the body member or any member fixed thereto. Also said second series of ridges can be disposed on the surface of the second jaw or any member fixed therto. However, the two series of ridges must be arranged to be selectively mated each other for prohibiting the relative movement of the body and the second jaw, when predetermined gripping force is applied to the gripping surface of the second jaw. More particularly, they are mated each other when the first and the second means of the guide means are disengaged so that the second jaw is prohibited to move back relative to the body, and they are not mated each other when the first and the second means of the guide means are engaged so that the second jaw is allowed to move to-and-fro for adjusting the slotwidth. Any known structures can be utilized for enabling such operation. Each of first and second series of ridges can be a series of parallel ridges which extend in parallel to the intersecting line formed by the median plane of the slot and the guide plane. However it is found to be preferable that each of the first and the second series of parallel ridges extend in the direction inclined to the intersecting line so that they can provide wider abutting surfaces to detent surely the second jaw against the body.
Also it has been found more preferable that each of the first and second series of ridges is formed in a chevron pattern, since they can provide more wider abutting surfaces within the limited width of the portions of the body and the second jaw or any members fixed thereto.
In accordance with the present invention, driving means is p_referablly comprises a hydraulic cylinder one end of which Is pivoted on a pin secured to the body member and the other end of which is pivoted on a pin secured to the second jaw, a pump for supplying pressure oil to the cylinder through piping, and an oil reservoir for receiving oil drained from the sylinder and for supplying oil to the pump through piping. The hydraulic cylinder can be a conventional type, and if necessary, can be of a specific type which has a function for locking the rod when presuure oil is not introduced in the cylinder. The pump can be operable manually or any other means.
The merit of using a hydraulic cylinder is that the limitation to empty weight of the clamp and/or limitation to attitude of clamp in use referred in the above can be eliminated. Another merit is that the driving means is easily operable by one touch operation without requiring stractural members such as rocking arm, extensible arm, recilient means, and stopper which are required in another embodiment of the present invention described hereinafter.
The driving means in acordance withe another embodiment of the present invention may comprise at least a rocking arm having a pin secured thereon and pivotably supported on the body in cantilevered fashion, at least a stopper for limiting the pivotal movement of the rocking arm within a predetermined angle, and an extensible arm, for example, comprising a rod, a sleeve for slidably receiving one end of the rod therein and interconnecting means for defining the longest length of the extensible arm at least one end of which is pivoted on a pin secured to either of the rocking arm or the second jaw with intervention of a recilient means for biasing the second jaw toward the slot and the other end of which is pivoted on a pin secured to the other of the second jaw or the rocking arm. Certainly another type of extensible arm can be utilized for the same purpose. The rocking arm is stopped by the stopper at two positions, one for keeping the second jaw at its retracted position and the other for keeping the second jaw at its advnced position. During the pivotal movement of the rocking arm, it is necessary to pass a dead point so that the rocking arm is latched at the respective positions.
In the preferred embodiment of the present invention, on one of the leg portions is provided with safety cam means which is operable, when the material gripped slipp out of the clamp, in such a manner that the toothed cam surface of the safety cam may bite into the surfaces of the material for avoiding slipping out accident with sacrificing the merit of non-damaging clamp.
The invention having been generally described, certain specific embodiments will now be described in detail with reference to the accompanying drawings in which:

Fig. 1 is a front elevation of a lifting clamp in accordance whith one of the embodiments of the invention;
Fig. 2 is an enlarged fragmental view of one of leg portions;
Fig. 3 shows diferent patterns of ridges;
Fig. 4 is a front elevation of a lifting clamp in accordance with another embodiment of the invention;
Fig. 5 is a front elevation of a lifting clamp in accordance with a further embodiment of the invention;

Referring now to Fig. 1, a clamp in accordance with one of embodiments of the invention comprises body member 10, a shackle 20, a first jaw 30, link means 40, and a slot width adjusting mechanism which comprises a second jaw 50, guide means 60, driving means 70, and detention means 80.
Body member 10 has a pair of leg portions 11 defining therebetween a slot S for receiving a material (not shown) to be lifted.
Shackle 20 has an eye 21 for attachment to a lifting cable (not shown).
First jaw 30 is disposed on one of leg portions 11.
Link means 40 comprises a bell crank arm 41 and link arm 42. Bell crank arm 41 is pivoted on a pin 41a secured to the body and is connected to the shackle with a pivot pin 22 and to one end of link arm 42 with a pin 41b secured to the bell crank arm which extends into an elongated hole 42a formed at the end of link arm. Link arm 42 is pivoted on a pin 42b secured on the body at its other end. On the intermediate portion between the elongated hole 42a and the pin 42b. first jaw is pivoted on a pin 42c. Thus first jaw 30 is linked with shackle 20.
Second jaw 50 has a flat gripping surface 51 parallel to the median plane M of slot S and a rear surface 52 inclining to the median plane at an acute angle 8 convexed to opening So of the slot to thereby form a wedge like profile. Second jaw is movable along a guide plane G between the retracted position shown by dotted line and the advanced position shown by fiction line.
Guiding means 60 comprises a guid plate 61 as first means having a guide surface 61a defining guide plane G inclining to the median plane M at an acuteangle 6 convexed to the opening So of the slot, and second means comprising a sliding plate 61b, a pair of guide pins which are secured on the rear surface 52 of second jaw 50 and a pair of nuts 61d for defining a guided plane. Guide plate 61 is provided with a slit (not shown) in which guide pins 61c are received. Sliding plate 61b is provided with a pair of holes for receiving the guide pins. The free ends of guide pins 61c are threaded for receiving nuts 61d thereon leaving predtermined play in the axial direction of the pins to thereby allow selective engagement of the first means and the second means. Thus the second jaw is guided along the guide plane with play.
Driving means 70 in this embodiment is shown as a hydraulic cylinder 71 one end of which is pivoted on a pin secured to the body and the other end of which is pivoted on a pin 71b secured to the second jaw. A pump for supplying pressur oil to cylinder 71 and piping therefor and an oil reservoir for receiving oil drained from the cylinder and for supplying oil to the pump as well as piping therefor are not shown, but they are actually disposed on the body.
Referring to Figs. 1 and 2, detention means 80 in this enbodiment comprises a first series of parallel ridges 81a extending in parallel to the intersection line formed by median plane M and guide plane G and disposed on the surface of the guide plate facing to the slot, and a second series of parallel ridges 81b extending in the same direction and disposed on rear srface 52 of the second jaw. Each of the ridges is defined with a first surface Fs which extends in a plane parallel to median plane M or inclined thereto at an acute angle convexed toward bottom Sb of the slot less than 5° and a second surface Ss which extends in a plane perpendicular to the median plane or inclined thereto at an acute angle convexed toward the opening So of the slot less than 90° . First and second series of ridges are complemcntal in shape and in dimensions.
In operation, a material is inserted into the slot, and then driving means 70 is actuated to advance second jaw 50 into the slot, the second jaw is guided along guide plane G with chattering the mating ridges, since guide means is provided with play, untill gripping surface 51 contacts with the material. When the second jaw is further advanced into the slot, the second jaw is laterally pushed by the material thereby first and second series of ridges 81a and 81b mtae each other for prohibiting relative movement of the second jaw and the body.
In order to eliminate wearing of the mating ridges, recilient means 90 such as coil springs 91 one of which is shown in Fig. 2 can be provided between guide plate 61 and second jaw. Coil spring 90 is disposed around the pin 61c and between guide plate 61 and second jaw 50. When a load overcomming the urging force of spring 91 is applied to the gripping surface, the second jaw is laterally moved (to the right in Fig. 2) and the mating ridges are engaged each other. Alternatively when a load overcomming the urging force is not applied to the griiping surface, the mating ridges are disengaged and second jaw is slidable along the guide plane.
It will be understood that the slot-width adjustment mechanism of this embodiment can be utilized for a clamp having a heavy empty weight regardless of the attitude of the clamp, since a hydraulic cylinder is used as driving means. When a specific hydraulic cylinder which has a function for locking the rod previously referred to is utilized, slipping out accident can be avoided upon unintentional pressure drop due to failuor of the hydraulic system.
In the first embodiment, first and second series of ridges are described as they are disposed. on the surface, facing to the slot, of guide plate 61 and on the rear surface 52 of second jaw 50, and ridges extend in parallel to the intersection line formed by median plane M and guide plane G. However, ridges can be disposed on other surfaces, for example, each of the opposing surfaces of a pair of side plates of the body is provided with a shoulder having a surface facing to the slot and inclined to the median plane, and the second jaw is provided with a pair of complemental shoulders each having inclined surface on its opposite sides, the series of ridges can be disposed on the surfaces of the shoulders. It has been found that when the width of the surfaces on which ridges are to be formed are relatively narrow, it is preferrable to provide series of parallel ridges extending with an inclination to the intersection line at an acute angle preferrably less than 30.. More preferablly, series of ridges are formed in a chevron pattern. In Fig. 3, (a) shows a rear surface of a second jaw having a series of parallel ridges extending in parallel to intersection line I , (b) shows a rear surface having a series of parallel ridges extending with an inclination to the intersection line, and (c) shows a surface having a series of chevron ridges. In the case of chevron ridges, a groove 81c can be formed on the center line as shown in Fig.3 (c) for the convenience of manufacturing.
In Fig.4, a front elevation of a lifting clamp in accordance with another embodiment of the invention. In this embodiment, driving means 50 comprises a pair of rocking arms 101, an extensible arm comprising a rod 102 and a sleeve 103, recilient means 104, a stopper 106, and a crank lever 107. More particularly, Each of rocking arms 101 has a pin 108 secured thereto which is pivotably received on one of opposing surfaces of side plate of the body. One end of rod 102 is pivoted on a pin 109 secured to a pair of rocking arms between the opposing surfaces thereof. One end of sleeve 103 is pivoted on a pin 110 secured to second jaw 50. Other end of rod 102 having a head is inserted into the other end of sleeve 103 having a cap for restraining the head within the sleeve to thereby define the muximum extention length of the extensible arm. Recilient means 104 which is shown as a coil spring is disposed around the extensible arm and the opposite ends of the spring are supported on escutchions secured to the rod and sleeve thereby the extensible arm tend to extend constantly. Stopper 106 is secured to the body in the vicinity of rocking arms so as to provide two extreme positions of pivotal movement of rocking arms 101 for driving the second jaw to-and-fro along the guide plane. Suitable arrangement of relative positions of pins 108 - 110 and stopper 106 may provide latching function to the driving means. Crank lever 107 is secured to the pin 108 at its end which extend to the out side of one of side plates of the body.
In the embodiment shown in Fig.4, there is provided a locking lever 120 for locking shackle 20 at its deepest nesting position when rocking arms 101 is stopped at its retracted position. Locking lever 120 is pivoted on a pin 121 secured to the body and has two arms 120a and 120b. Arm 120a has a path of pivotal movement intefereing with the path of pivotal movement of the shackle and/or bell crank arm 41. Arm 120b has a path of pivotal movement interfereing with the path of pivotal movement of rocking arms 101. It will be apparent that suitable arrangement of the pathes of pivotal movement as shown in Fig. 4 may provide the aimed locking function.
Referring now to Fig.5, a clamp according to a further embodiment of the invention is illustrated wherein rocking arms are somewhat modified for serving the functions of rocking arms 101 and locking arm 120 of Fig. 4. A pair of rocking arms 130 in this embodiment have a mushroom like profile defined with a circular arc 131 and a pair of recesses 132a and 132b disposed on a pair of radiis. Each of rocking arms has a pin 133 secured thereto at its center and is pivotably supported on one of opposing surfaces of side plstes of the body. Stopper 106 is secured to the body to engage with the recesses 122a and 122b for providing two extreme positions of pivotal movement of the rocking arms. The circular arc 131 has a path of pivotal movement interfereing with that of shackle 20 and/or bell crank arm 41.
In the embodiment of Fig. 5, there is provided a safety cam means which comprises a pair of safety cams 140, an L shaped arm 141, a lever arm 142, recilient means 143 and a crank lever (not shown).
Before entering into detailed explantion of the safety cam meant, additional explanation of link means 40 will be needed for better understanding of the safety cam means. A pair of link arms 42 are pivoted on a pin 42b secured to the body. First jaw is pivoted on a pin 142c secured to and between the link arms.
Now reverting to the detailed explantion of the safety cam means, a pair of safety cams 140 are pivoted on pin 42b sandwiching link arms 42 therebetween. Each of safety cams 140 has eccentric cam surface 140a having tooth on the side facing to the slot and a tail 140b on the opposite side. L shaped arm 141 Is pivoted on a pin 140c secured to and between tails 140b of the safety cams. Lever arm 142 has a pin 142a secured to one end thereof and said pin is pivotably supported to the body. The other end 142b of lever arm 142 is forked into two portions between which the corner of L shaped arm 141 is received and pivoted on a pin 142c secured to end 142b. Free end of L shaped arm 142 extends toward the bottom Sb of the slot. Recilient means 143 is illustrated as a tension coil spring one end of which is secured to the pin 140c between safety cams 140 and the othe end of which is secured to a pin 144 fixed to the body. The arrangement of pins 140c, 142a and 142c is such that pin 142c may move accross the line passing through pins 140c and 142a as lever arm is pivoted on pin 142a. It will be understood that L shaped arm 141 located at the position illustrated with dotted line in Fig. 5 tend to pivote lever arm 142 clockwisely by means of tension spring 143, since pin 142c is located at left side of the line passing through pins 140c and 142a. However they are latched at that position, since L shaped arm is stopped by pin 144. When lever arm 142 is pivoted counterclockwise in Fig. 5, pin 142c move accross the line to right side and free end 142d of the L shaped arm is moved toward the bottom Sb of the slot untill it is stopped by materials inserted in the slot or gripping surface 51 of the second jaw. When free end 142d of the L shaped arm is stopped by the material inserted in the slot, eccentric toothed surfaces 140a of the safety cams is kep not to contact with the material. When the material slip toward opening So of the slot, free end 142d is moved into the slot and toothed cam surfaces are allowed to contact with the slipping material.
From the foregoing description taken with the accompanying drawings, it will be apparent to those skilled in the art that many modifications of the slot-width adjustment mecanism can be made within the spirit of the present invention.

Claims

1. A lifting clamp comprising:

a) a body member having a pair of leg portions defining therebetween a slot to receive a material to be lifted;

b) a first jaw disposed on one of the leg portions;

c) a shackle for attachment to a lifting cable and movable relative to the body;

d) link means for oparatively linking the shackle to the first jaw adapted to translate the lifting force applied to shackle into gripping force;

e) a second jaw disposed on the other leg portions and movable relative to the body with keeping its flat gripping surface parallel to the median plane of the slot;

f) guide means comprising: first means fixed to the body for defining a guiding plane inclined to the median plane of the slot at an acute angle convexed toward the opening of the slot; and second means fixed to the second jaw for defining a guided plane adapted cooperatively to engage with the first means for guiding the second jaw along the guide plane and adapted to provide with predetermined play for allowing the second means to be disengaged from the first means;

g) detention means comprising: a first series of ridges disposed fixedly to the body along a plane substantially parallel to the guide plane and a second series of ridges disposed fixedly to the second jaw along a plane substantially parallel to the guide plane and adapted selectively to mate with the first series of ridges for prohibiting relative movement of the body and the second jaw; and each of said ridges is defined with a first surface which extends in a plane parallel to the median plane or inclined thereto at an acute angle, convexed toward the bottom of the slot, less than 5° and a second surface which extends in a plane perpendicular to the median plane or inclined thereto at an acute angle toward the opening of the slot less than 90° ; and

h) driving means for driving the second jaw to-and fro, with respect to the body, along the guide plane, when the first and second series of ridges are disengaged.

2. The lifting clamp of Claim 1, wherein said body member comprises a pair of side plates between which a support plate is fixedly disposed along a plane inclining to the median plane of the slot at an acute angle convexed toward opening of the slot and said detention means comprises:

a) a first series of parallel ridges disposed on the surface, of the support plate, facing to the second jaw;

and

b) a second series of parallel ridges disposed on the surface, of the second jaw, extending substantially parallel and facing to the support plate.

3. The lifting clamp of Claim 2, wherein said first and second series of parallel ridges extend in parallel to the intersection line formed by the guide plane and the median plane.

4. The lifting clamp of Claim 2, wherein said first and second series of parallel ridges extend, on the respective surfaces, in the direction inclined to the intesecting line of the guide plane and the median plane at an acute angle less than 30° .

5. The lifting clamp of Claim 1, wherein said body member comprises a pair of side plates between which a support plate is fixedly disposed along a plane inclined to the median plane of the slot at an acute angle convexed toward the opening of the slot and said detention means comprises:

a) a first series of ridges each having a pattern of chevron disposed on the surface, of the support plate, facing to the second jaw; and

b) a second series of ridges each having a pattern of chevron disposed on the surface of the second jaw facing to the support plate.

6. The lifting clamp of any of preceeding Claims, wherein said driving means comprises:

a) a hydraulic cylinder one end of which is pivoted on a pin secured to the body member and the other end of which is pivoted on a pin secured to the second jaw;

b) a pump for supplying pressure oil to the cylinder through piping;

c) ^- an oil reservoir for receiving oil drained from the cylinder and for supplying oil to the pump through piping.

7. The lifting clamp of any of Claim 1 through 6, wherein said driving means comprises:

a) at least a rocking arm pivoted on a pin secured to the body in cantilevered fashion;

b) at least a stopper for limitting the rotational movement of the arm within a predetermined angle;

c) an extensible arm comprising: a rod, a cylinder for slidably receiving one end of the rod therein, and interconnecting means for defining the longest length of the extensible arm at least one end of which is pivoted on a pin secured to either of the rocking arm or the second jaw with intervention of a recilient means for biasing the second jaw toward the slot and the other end of which is pivoted on a pin secured to the other of the second jaw or the rocking arm.

8. The lifting clamp of claim 7, wherein:

a) a pair of rocking arm being provided, each having a mushroom like profile defined with a circular arc and a pair of recesses, and each having a first pin secured thereto at its center which is pivotably received on one of the side plates of the body member in cantilevered fashion;

b) one end of said extensible arm being pivoted on a second pin secured to the second jaw and the other end thereof being pivoted on a third pin secured to and between the rocking arms;

c) at least a stopper secured to the body on the path of pivotal movement of the recesses of the rocking arms and adapted to engage therewith for defining the limitations of pivotal movement of the rocking arms; and

d) said first, second and third pins as well as said recesses and stopper being so arranged that the third pin is located on one side of the line passing through the first and the second pins when the rocking arms are stopped at one of the limitations of pivotal movement of the rocking arms and the third pin is located on the other side of the line passing through the first and the second pins when the rocking arms are stopped at the other of the limitations of the pivotal movement of the rocking arms.

9. The lifting clamp of Claim 7, wherein:

a) a pair of rocking arm being provided each having a first pin secured thereto at its center which is pivotably received on one of the side plates of the body member in cantilevered fashion;

c) a stopper secured to the body on the path of pivotal movement of the rocking arms and adapted to engage therewith for defining the limitations of the pivotal movement of the rocking arms;

d) a bell crank lever being further provided which is pivoted on a pin at its intermediate portion secured to the body in the vicinity of the rocking arms and shackle and/or link means for linking the first jaw to the shackle, and which has a first free end having its path of movement crossing with the path of movement of the thid pin and a second free end having its path of movement crossing with the path of movement of the shackle and/or link means;

e) said first, second and third pins as well as said rocking arms and stopper being so arranged that the third pin is located on one side of the line passing through the first and the second pins when the rocking arms are stopped at one of the limitations of pivotal movement of the rocking arms and the third pin is located on the other side of the line when the rocking arms are stopped at the other of the limitations of the pivotal movement of the rocking arms; and

f) said first and second free ends of the bell crank lever, the third pin and the shackle and/or link means being so arranged that when the rocking arms are stopped at one of the limitations of their pivotal movement for positioning the second jaw at its retracted position and when the shackle is located at its most deepest nesting position, the first free end of the bell crank lever engages with a part of shackle and/or link means, and the second free end of the bell crank lever engages with the third pin for prohibiting the pivotal movement of the bell crank lever to thereby prohibit the relative movement of the shackle and the body member, and that when the rocking arms are stopped at the other of the limitations of their pivotal movement for positioning the second jaw at its advanced position, the third pin is moved out of the path of movement of the second free end of the bell crank lever for allowing the pivotal movement of the bell crank lever to thereby allow the shackle and the link means to move relative to the body member.

10. The lifting clamp of any of Claims 1 - 9, wherein recilient means further provided which is adapted to urge the second jaw to engage the first and the second means of the guid means and disengage the first and the second series of ridges for guiding the second jaw along the guiding plane when a load overcomming the urging force is not applied to the gripping surface of the second jaw, and adapted to be yielded to disengage the first and second means of the guide means and to allow the first and the second series of ridges to be engaged for prohibiting the relative movement of the second jaw and the body member.

11. The lifting clamp of Claim 10, wherein:

a) said body member comprises a pair of side plates between which a support plate is fixedly disposed along a plane inclining to the median plane of the slot at an acute angle convexed toward theopening of the slot;

b) said support plate being provided with a slit extending in the direction of the movement of the second jaw;

c) said second jaw is disposed in the vicinity of the support plte on the side of the slot;

d) said detention means is disposed on a surface of the support plate facing to the slot and the second jaw;

e) said guide means comprises: at least two guide pins secured to the second jaw and extending through the slit; a slide plate connected to the guide pins for sliding engagement to the other surface of the support plate opposite to the slot with predetermined play for allowing selective engagement of the detention means;

f) said recilient means comprises at least two coil springs each disposed around one of the guide pins, and between the support plate and the second jaw.

12. The lifting clamp of Claims 1 - 11, wherein a safety cam mechanism is further provided which comprises:

a) a safety cam pivoted on a fourth pin secured to the body member having an exentric toothed surface extending from the fourth pin toward the bottom of the slot and a tail oppositly extending from the fouth pin adapted to bite into the surfaces of the article when it tend to slip off the clamp ;

b) a latch lever pivoted on a pin secured to the body member on its one end;

c) an L shaped arm pivoted on a fifth pin secured to the free end of the latch lever at its corner portion and having first and second arms angularly extending from the corner, the end of the first arm is pivoted on a pin secured to the tail of the safety cam, and the end of the second arm is extending toward the bottom of the slot;

d) recilient means urging the safety cam to be rotated in the direction for engaging the excentric toothed surface, and urging the L shaped arm to be rotated in the direction for engaging the end of the second arm thereof to the a:ticle clamped by the clamp at the bottom area of the sot, to thereby allow the L shaped arm and the safety cam to be roteted when the article gripped in the slot is slipped.

13. A lifting clamp comprising a body member (10) having a pair of leg portions (11) defining therebetween a slot(s) for receiving an element to be lifted, jaw means comprising a first jaw (30) on one leg and a second jaw (50) on the other leg, the jaws being relatively adjustable on the body for gripping the element between the jaws, the second jaw being adjustable along a guide (61a) provided on the body and extending towards the mouth of the slot at an acute angle to the slot, a lifting member (20) movably mounted on the body and link means (41,42) connected between the lifting member and the jaw means (30,50) whereby the lifting member relatively urges the jaws towards each other so that lifting force is translated to gripping force, characterised by detention means (80) for securing the second jaw to the body in selected adjustment positions, the second jaw and the body having formations (81a, 81b) which permit adjustment of the second jaw along the guide until a gripping force is exerted, the arrangement being such that the reaction to the gripping force urges the formations into engagement to prevent reverse movement of the second jaw.

1. A lifting clamp of the type comprising: a body member having a pair of leg portions defining therebetween a slot to receive a material to be gripped; a first jaw disposed on one of the leg portions; a shackle for attachment to a lifting cable and movable relative to the body; link means for operatively linking the shackle to the first jaw adapted to translate the lifting force applied to shackle into gripping force; a second jaw disposed on the other leg portion and movabTe relative to the body with keeping its flat gripping surface parallel to the median plane of the slot; guide means comprising first means fixed to the body far defining a guiding plane inclined to the median plane of the slot at an acute angle convexed toward the opening of the slot and second means fixed to the second jaw for defining a guided plane adapted cooperatively to engage with the first means for guiding the second jaw along the guide plane and adapted to provide with predetermined play for allowing the second means to be disengaged from the first means; detention means comprising a first series of ridges disposed fixedly to the body along a plane substantially parallel to the guide plane and a second series of ridges disposed fixedly to the second jaw along a plane substantially parallel to the guide plane and adapted selectively to mate with the first series of ridges for prohibiting relative movement of the body and the second jaw; biasing means for normally urging the second jaw along the guide plane in the direction toward the opening of the slot; locking means adapted to prohibit the relative movement of the first and second jaws at least in the situation wherein the distance between the gripping surfaces of first and second jaws is largest; and driving means for driving said second jaw to-and-fro along the guide plane;
characterised in that:

each of said ridges is defined with a first surface which extends in a plane parallel to the median plane or inclined thereto at an acute angle, convexed toward the bottom of the slot, less than 5° and a second surface which extends in a plane perpendicular to the median plane or inclined thereto at an acute angle toward the opening of the slot less than 90°.

2. A lifting clamp according to Claim 1, characterised in that said body member comprises a pair of side plates between which a support plate is fixedly disposed along a plane inclining to the median plane of the slot at an acute angle convexed toward opening of the slot, and said first and second series of parallel ridges extend, on the respective surfaces, in the direction inclined to the intersection line of the guide plane and the median plane at an acute angle less than 30°.

3. A lifting clamp according to Claim 1, characterised in that said body member comprises a pair of side plates between which a support plate is fixedly disposed along a plane inclining to the median plane of the slot at an acute angle convexed toward the opening of the slot and said detention means comprises:

4. A lifting clamp according to any preceding claim, characterised in that said drive means comprises:

b) a pump for supplying pressure oil to the cylinder through piping;

c) an oil reservoir for receiving oil drained from the cylinder and for supplying oil to the pump through piping.

₅. A lifting clamp according to any preceding claim, characterised in that said driving means comprises:

b) at least a stopper for limiting the rotational movement of the arm within a predetermined angle;

c) an extensible arm comprising: a rod, a cylinder for slidably receiving one end of the rod therein, and interconnecting means for defining the longest length of the extensible arm at least one end of which is pivoted on a pin secured to either of the rocking arm or the second jaw with intervention of a resilient means for biasing the second jaw toward the slot and the other end of which is pivoted on a pin secured to the other of the second jaw or the rocking arm.

6. A lifting clamp according to Claim 5, characterised in that:

a) a pair of rocking arms are provided, each having a mushroom like profile defined with a circular arc and a pair of recesses, and each having a first pin secured tnereto at its center which is pivotably received on one of the side plates of the body member in cantilevered fashion;

d) said first, second and third pins as well as said recesses and stopper being so arranged that the third pin is located on one side of the line passing through the first and the second pins when the rocking arms are stopped at one end of the limitations of pivotal movement of the rocking arms and the third pin is located on the other side of the line passing through the first and second pins when the rocking arms are stopped at the other of the limitations of the pivotal movement of the rocking arms.

7. A lifting clamp according to Claim 5, characterised in that:

a) a pair of rocking arms being provided each having a first pin secured thereto at its center which is pivotably received on one of the side plates of the body member in cantilevered fashion;

d) a bell crank lever being further provided which is pivoted on a pin at its intermediate portion secured to the body in the vicinity of the rocking arms and shackle and/or link means for linking the first jaw to the shackle, and which has a first free end having its path of movement crossing with the path of movement of the third pin and a second free end having its path of movement crossing with the path of movement of the shackle and/or link means;

e) said first, second and third pins as well as said rocking arms and stopper being so arranged that the third pin is located on one side of the line passing through the first and second pins when the rocking arms are stopped at one of the limitations of pivotal movement of the rocking arms and the third pin is located on the other side of the line when the rocking arms are stopped at the other of the limitations of the pivotal movement of the rocking arms; and

f) said first and second free ends of the bell crank lever, the third pin and the shackle and/or link means being so arranged that when the rocking arms are stopped at one of the limitations of their pivotal movement for positioning the second jaw at its retracted position and when the shackle is located at its most deepest nesting position, the first free end of the bell crank means, and the second free end of the bell crank lever engages with the third pin for prohibiting the pivotal movement of the bell crank lever to thereby prohibit the relative movement of the shackle and the body member, and that when the rocking arms are stopped at the other of the limitations of their pivotal movement for positioning the second jaw at its advanced position, the third pin is moved out of the path of movement of the second free end of the bell crank lever for allowing the pivotal movement of the bell crank lever to thereby allow the shackle and the link means to move relative to the body member.

8. A lifting clamp according to any preceding claim, characterised in that:

resilient means is further provided which is adapted to urge the second jaw to engage the first and second means of the guide means and disengage the first and second series of ridges for guiding the second jaw along the guiding plane when a load overcoming the urging force is not applied to the gripping surface of the second jaw, and adapted to be yielded to disengage the first and second means of the guide means and to allow the first and second series of ridges to be engaged for prohibiting the relative movement of the second jaw and the body member.

9. A lifting clamp according to Claim 8, characterised in that:

a) said body member comprises a pair of side plates between which a support plate is fixedly disposed along a plane inclining to the median plane of the slot at an acute angle convexed toward the opening of the slot;

c) said second jaw is disposed in the vicinity of the support plate on the side of the slot;

f) said resilient means comprises at least two coil springs each disposed around one of the guide pins, and between the support plate and the second jaw.

10. A lifting clamp according to any preceding claim, characterised in that a safety cam mechanism is further provided which comprises:

a) a safety cam pivoted on a fourth pin secured to the body member having an eccentric toothed surface extending from the fourth pin toward the bottom of the slot and a tail oppositely extending from the fourth pin adapted to bite into the surface of the article when it tends to slip off the clamp;

b) a latch lever pivoted on a pin secured to the body member on its one end;

c) an L-shaped arm pivoted on a fifth pin secured to the free end of the latch lever at its corner portion and having first and second arms angularly extending from the corner, the end of the first arm is pivoted on a pin secured to the rail of the safety cam, and the end of the second arm is extending toward the bottom of the slot;

d) resilient means urging the safety cam to be rotated in the direction for engaging the eccentric toothed surface, and urging the L-shaped arm to be rotated in the direction for engaging the end of the second arm thereof to the article clamped by the clamp at the bottom area of the slot, thereby allow the L-shaped arm and the safety cam to be rotated when the article gripped in the slot is slipped.

11. A lifting clamp comprising a body member (10) having a pair of leg portions (11) defining therebetween a slot(s) for receiving an element to be lifted, jaw means comprising a first jaw (30) on one leg and a second jaw (50) on the other leg, the jaws being relatively adjustable on the body for gripping the element between the jaws, the second jaw being adjustable along a guide (61a) provided on the body and extending towards the mouth of the slot at an acute angle to the slot, a lifting member (20) movably mounted on the body and link means (41, 42) connected between the lifting member and the jaw means (30, 50) whereby the lifting member relatively urges the jaws towards each other so that lifting force is translated to gripping force, characterised by detention means (80) for securing the second jaw to the body in selected adjustment positions, the second jaw and the body having formations (81a, 81b) which permit adjustment of the second jaw along the guide until a gripping force is exerted, the arrangement being such that the reaction to the gripping force urges the formations into engagement to prevent reverse movement of the second jaw.