HYDRAULIC CLAMP WITH A SWINGING CLAMP ARM

Abstract: A hydraulic clamp for fixing workpiece/s on the table of a machining centre, comprises a clamp arm (4) and hydraulic cylinder (5) arranged one before the other longitudinally in a clamp housing (3). The clamp arm (4) is pivotally supported near its lower end to be freely swingable longitudinally. An elastic body (32) is provided to extend from the clamp arm (4) at the middle in height to a constituent member of the hydraulic cylinder (5) so that the clamp arm (4) is pushed back to be inward of the front face of the clamp housing (3) in the absence of oil pressure, while the clamp arm (4) is driven forward by a piston (14) of the hydraulic cylinder (5) to be beyond of the front face thereof in the presence of a sufficient oil pressure.

Description: This invention relates to a hydraulic clamp for securing a workpiece to a work-holding plate such as the table or work-pallet of a machining centre. More particularly it relates to hydraulic clamps having a clamp arm and a hydraulic cylinder arranged in a clamp housing one before the other longitudinally so that the clamp arm is swung longitudinally by the hydraulic cylinder. There is known from Japanese laid-open utility model application No. 191227/'84, a construction which is shown in figure 8. In this figure there is shown a hydraulic clamp in which the clamp arm 204 is pivotally supported by the clamp housing 203, the clamp arm 204 being clamp-actuated by the extending force of the hydraulic cylinder 205. However, in this prior art the hydraulic cylinder 205 provided in the clamp housing is constituted as double-acting type, so that it has a structure which does not require the return spring and the spring holding pin. Although of interest, it should be noted that this disclosure does not relate to a single-actuated hydraulic cylinder with which the present invention is concerned. Another known construction was brought to the Inventor's attention in a catalogue of A101 SEIKI Inc, advertised under the name PASCAL (RTM) clamp. The construction is illustrated in figures 9 and 10. The clamp housing 203 is secured to the work pallet 201 by the use of fastening bolts 237, and the piston 214 is driven forward hydraulically to cause the clamp arm 204 to swing forward (as shown in the figure by two-dot chain line) thereby to secure the workpiece W to the work holding jig 201a. A turning moment is created by the clamp reaction force R applied by the workpiece W to the clamp arm 204 which causes the clamp to turn about its rear edge 260 which acts as a fulcrum, so that the clamp in the above-described condition pushes up the clamp housing. Meanwhile, the clamp housing 203 is kept pressed against the work pallet 201 by a plurality of front and rear fastening bolts 237. Of the fastening forces, the front fastening force induces a moment which acts on the clamp housing 203 pushing it downwards about its rear edge 260, counter-acting the above-mentioned turning moment, so that the clamp housing 203 stays on the work pallet 201. Previously, and as illustrated in figures 9 and 10 the holes 238 for the front fastening bolts 237 were made behind the pin supporting holes 228 for the spring holding pin 225. That is, a pair of pin supporting holes 228 were made in the left and right walls of the clamp housing 203 with their centres on a transverse line. An anti-interference groove 230 was provided through the piston rod 220 from a portion on one peripheral side to a portion on other peripheral side so that the spring holding pin 225 could be set through laterally the pin supporting holes 228 and the groove 230. Interference is prevented between the pin-supporting holes 228 or the fulcrum holes 208 for the fulcrum pin 209 and the through holes 238 for the front fastening bolts 237, these through holes 238 for the front fastening bolts 237 could only be made towards the rear end of the clamp housing 203. The prior art construction described above has the following problems. (a) Since the through holes 238 for the front fastening bolts 237 could be made only towards the rear end of the clamp housing 203, the arm length of the moment resulting from the fastening force of the front fastening bolts 237 was inevitably short. Hence, the moment pushing the clamp housing 203 down is also small, and unable to secure the clamp housing 203 firmly to the work pallet 201 against the inverting moment caused by the clamp's reaction force R. (b) The holes 238 for the fastening bolts 237 are made to pass through the clamp housing 203 vertically, and the pin supporting holes 228 are made to pass through the clamp housing 203 sideways. Therefor the access directions for drilling these pairs of holes 238, 228 are different, resulting in an increased number of work steps involved as well as a lot of effort therefor. The present invention aims to provide a structure which enables the clamp housing to be firmly secured to the work clamping plate. It also aims to provide a clamp which requires less work steps to make the aforesaid holes in the clamp housing. The present invention is defined in the claims and is characterised in that a pair of pin-supporting holes are made substantially vertically in the top and bottom walls of the clamp housing and the anti-interference groove is made substantially vertically through the piston rod from an upper to a lower peripheral portion whereby the through holes for the front fastening bolts are located on both left and right sides of the spring holding pin. In the clamp embodying the invention, the front fastening bolt holes are safe from interference with the pin-holding holes for the spring holding pin. It is, therefore, possible to distribute the bolt holes nearer to the front edge of the clamp housing. This results in an increased arm length for the moment of fastening force for the fastening bolts in the front row with respect to the rear edge of the clamp housing which acts as the fulcrum for inversion. Hence the hydraulic clamp is fixed securely to the work pallet. Moreover, since the pin-holding holes for the spring holding pins are provided as through holes in the same direction as the holes for the fastening bolts, it is possible to drill these two types of holes as well as the pin holding holes from the same side as the holes to be made in the clamp housing. Hence, the number of working steps to produce the clamp can be decreased so that less effort is required for manufacturing the hydraulic clamp. FIGS. 1 to 7 show embodiments of the present invention, while FIGS. 8 to 11 show prior art constructions. FIGS. 1 to 3 show a first embodiment of the present invention, of which FIG. 1 is a longitudinal side sectional view of a hydraulic clamp; FIG. 2 is a front elevation of the hydraulic clamp; and FIG. 3 is a plan view of the hydraulic clamp; FIG. 4 is a view showing a second embodiment, being equivalent to FIG. 1; FIGS. 5 to 7 show a third embodiment, of which FIG. 5 is a plan view of a multiple hydraulic clamp, FIG. 6 is a sectional view taken along line IX-IX of FIG. 5 and FIG. 7 is a partial sectional view taken along line X-X of FIG. 5; FIG. 8 is a longitudinal side sectional view of a hydraulic clamp according to a first prior art construction; and FIGS. 9 to 10 show a hydraulic clamp according to a second prior art construction of which FIG. 9 is a longitudinal side sectional view of the hydraulic clamp; and FIG. 10 is a front elevation of the hydraulic clamp. Referring to figures 1 to 3, reference numeral 1 is a work pallet, and a work W is fixed to a work holding jig la of this work pallet 1 by means of a hydraulic clamp 2. This hydraulic clamp 2 comprises a clamp housing 3 which is fixedly attached to the work pallet 1 and in the front portion of the clamp housing 3 is provided a claw-shaped clamp arm 4 and in the rear portion thereof is provided a hydraulic cylinder 5 for driving the clamp arm 4. In Fig.1 the solid line shows the arrangement in unclamped condition and the two-dot chain line shows that in clamped condition. Firstly, the clamp arm 4 will be described; the left and right walls 7, 7 of the clamp housing 3 extend forwardly and near their lower edge there are formed fulcrum holes 8, 8 with their centres aligned. The clamp arm 4 is placed between the extended side walls 7, 7 and a fulcrum shaft 9 is set through both fulcrum holes 8, 8 and another formed near the lower end of the clamp arm 4 in between. To this fulcrum shaft 9 the clamp arm 4 is fixedly secured by means of a setscrew 10 and thereby this clamp arm 4 is made freely swingable longitudinally and pivotally supported in the fulcrum holes 8, 8. There is provided a scra@er 11 in contact with the top end of the aforesaid clamp arm 4 as it swings. This scraper 11 is set out between the left and right walls 7, 7 and both ends of the scraper 11 are fixedly secured to both side walls 7, 7 by means of countersunk screws 12. Near the lower end of the clamp arm 4 there is provided a scraper 4b projecting therefrom, and this scraper 4b can be brought into contact with the work pallet 1. The hydraulic cylinder 5 will now be described. This hydraulic cylinder 5 is of the spring-return single acting type. In the clamp housing 3 there is provided a cylinder chamber 13 extending longitudinally, and into this cylinder chamber 13 a piston 14 is inserted oiltight and freely slidable. Behind this piston a drive chamber 15 is provided. Reference numeral 16 is a oil supply-discharge port and 16a is a spare port. also provided is a return spring 18 which urges the aforesaid piston 14 rearward. When the pressure oil is supplied to the drive chamber 15, the piston 14 is driven forward against the urging force of the aforesaid return spring 18, while, when the pressure oil is discharged from the drive chamber 15, the piston 14 is caused to retract by the urging force of the return spring 18. A cylinder piston rod 20 projects forwardly from the aforesaid piston 14 and an output part 21 at the forward end of this piston rod 20 comes into contact with the back of the clamp arm 4 at the point of application of force 22. The aforesaid return spring 18 is inserted into the cylindrical hole 23 of the piston rod 20. This return spring 18 consists of a compression coil spring and its rear end is held by the rear end 23a of the cylindrical hole 23 and, at the same time, the front end is held by the clamp housing 3 via a spring holding pin 25. A pair of aligned pin holding holes 28, 28 are provided in the top 3a and bottom 3b of the clamp housing 3 near the front end of the clamp housing 3, the piston rod 20 and the cylindrical hole 23 of the piston rod 23. The spring holding pin 25 is set between the aforesaid pin-holding holes 28, 28 to be held at both ends. The lower end of this spring holding pin 25 is secured to the clamp housing 3 with a setscrew 29. On the rear side of the middle portion of the vertically set spring holding pin 25 is formed a slot or recess 26 for holding the forward end of the return spring 18. The piston rod 20 has a pair of longitudinally extending slots 30, 30 formed in it to allow movement of the piston rod without interference with the spring holding pin 25. Both anti-interference slots 30, 30 are so formed to allow the pin 25 to pass through the upper peripheral wall section 20a and lower peripheral wall section 20b of the piston rod. Also, it is so designed that, when the piston 14 has moved forward, the piston rod 20 does not come into contact with the spring holding pin 25. In the above-described construction, an elastic body is provided for pushing back the clamp arm 4 to be inward of the front face. This elastic body here consists of cone-shaped tension coil spring 32 and is provided to extend from the middle portion in height of the clamp arm 4 to some constituent member of the hydraulic cylinder 5 located behind the clamp arm 4. That is, a nut 34 is screwed down on a bolt 33 to be secured to the middle portion in height of clamp arm 4, and to this nut 34 the front end of the coil of the tension coil spring 32 is connected by screwing . The rear end of the coil of the tension coil spring 32 is connected by screwing with the front end of cylindrical hole 23 of the piston rod 20 as a movable member of the hydraulic cylinder 5. The hydraulic clamp 2 of the above-described construction is fixedly secured to the work pallet 1 by the use of a pair each of fastening bolts 36, 37 for the front and rear portion thereof. This means that in the front part of the clamp housing 3 vertical pair of holes 38, 38 for fastening bolts are provided on both sides equidistant from the spring holding pin 25. Also, in the rear part of the clamp housing 3 vertical pair of holes 39, 39 for fastening bolts are provided on both sides. Fastening bolts 36, 37 are set through the aforesaid bolt holes 38, 39 respectively. Since, therefore, the front fastening bolt holes 38 are safe from interference with the pin-holding holes 28 for the spring holding pin 25, it is possible to distribute the bolt holes 38 nearer to the front edge of the clamp housing 3. This means an increased arm length for the moment of fastening force F for the fastening bolts 36 in the front row with respect to the rear edge 40 of the clamp housing as the fulcrum for inversion, hence the hydraulic clamp 2 is stongly fixed to the work pallet. Further, since the aforesaid pin-holding holes 28 for the spring holding pin 25 are provided as through holes in the same direction with the holes 38, 39 for the fastening bolts, it is possible to drill these two types of holes 38, 39 as well as the pin holding holes 28, 28 for the same side as the holes to be made in the clamp housing 3. Hence, the number of working steps can be decreased and less effort is required for manufacturing the hydraulic clamp 2. Referring now to figure 4, there is shown a second embodiment of the invention. In this embodiment a spring holding pin 63 is arranged to be upright and a holding jig 66 for the return spring is fixed to the spring holding pin 63 inside the cylindrical hole 65 of the piston rod 64 of the hydraulic cylinder 5. Between the holding jig 66 of the return spring 67 and the rear end wall 65a of the cylindrical hole 65 of the piston rod 64 is a return spring 67. This return spring 67 is a square-sectioned compression spring. An elastic body consisting of a tension coil spring 69 extend from the middle in height of a clamp arm 68 to the holding jig 66 for the return spring which is a fixed member of the hydraulic cylinder 5. A spring mount 70 is fixedly attached to the middle point in height of the clamp arm 68. The front end of the tension coil spring 69 is screwed to the spring mount 70 and the rear end of the tension coil spring 69 is screwed to the front end of the holding jig 66 for the return spring. FIGS. 5 to 8 show a third embodiment which uses a multiplicity of hydraulic clamps. In this embodiment a work pallet 101 is provided with a multiplicity of hydraulic clamps 102 so that a multiplicity of workpieces 104 can be clamped simultaneously. A clamp housing 103 is constructed using long square bars and has front and rear vertical through bolt holes 138, 139 for fixing by bolting. Front fastening bolts 136 are set through the front bolt holes 138 and rear fastening bolts 137 set through the rear bolt holes 139. The work pallet 101 has formed therein inverse T-sectioned grooves 134 in which a plurality of nuts 135 and a plurality of front and rear fastening bolts 136, 137 are set for fixing the clamp housing 103. In the aforesaid clamp housing 103 there are provided properly spaced in the longitudinal direction (transverse direction in FIG. 5 and 7) a plurality of clamp arms 104 and hydraulic cylinders 105. These parts or members are substantially the same as shown in the aforesaid embodiment 1. There are provided a plurality of clamp arm supporting frames 107 separate from the clamp housing 103, and each clamp arm supporting frame 107 is secured to the front portion of the clamp housing 103 by the use of fastening bolts 143. Near the lower end of each supporting frame 107 is a fulcrum hole 108 and a fulcrum shaft 109 is set through a supporting hole 104a of each clamp arm 104 and the fulcrum holes 108, 108 on both sides thereof. Each fulcrum shaft 109 is secured to the clamp arm 104 by means of setscrews 110. A scraper 111 makes contact with the swingable top of each clamp arm 104. The scraper is long and is secured to the top of each clamping arm supporting frame 107 by countersunk screws 112. Between the middle portion in height of the clamp arm 104 and a piston rod 120 is an elastic body consisting of a tension coil spring 132 by the use of bolts 133. Pin supporting holes 128 of spring holding pins 125 are arranged to pass through the clamp housing 103 in the same way as described above in the embodiment 1. Hence, whereas where an attempt is made to construct a multiplicity of hydraulic clamps using the known construction as described in the prior art 2 (See FIGS. 9 and 10), it is necessary to make long pin supporting holes 228 along the longitudinal direction of a long clamp housing 203, requiring a lot of effort, it suffices according to the preferred embodiment of the present invention to make pin supporting holes 128 spaced vertically, hence the length of each hole is smaller thus being easier to drill with simultaneous improvement in precision. The subject matter described herein is also described and claimed, in part, in our copending application 87308405.7 published as EP-A-0261945

Claims: A hydraulic clamp with a swinging clamp arm comprising a clamp arm (4) in the front part of a clamp housing (3), and a hydraulic cylinder (5) in the rear part thereof, said clamp arm (4) being pivotally supported by a fulcrum shaft (9) held in both side walls to be freely swingable, said hydraulic cylinder (5) consisting of a spring-return type single acting cylinder so arranged that in a cylinder chamber (13) a piston (14) is pushed back by a return spring (18) and, when a sufficient oil pressure is built up in said cylinder chamber (13), said clamp arm (4) is driven forward against urge of said return spring (18), an output part (21) of said piston rod (20) being brought into contact with the back of said clamp arm (4) at the point of application of force (22), said return spring (18) being inserted into a cylindrical hole (23) of said piston rod (20), the rear end of said return spring (18) being held by a rear end wall (23a) of a cylindrical hole (23) and the front end of the same being held by the mid portion (26) of a spring holding pin (25), said spring holding pin (25) being set through the clamp housing (3) and piston rod (20) as well as said cylindrical hole (23) of said piston rod (20) to be held at both ends thereof in a couple of pin supporting holes (28, 28) provided in said clamp housing (3), a longitudinal groove (30) being formed in said piston rod (20) for avoiding interference with said spring holding pin (25) and bolt holes (38, 39) being made vertically in said clamp housing (3) in the front and rear part thereof, characterised in that a pair of pin supporting holes (28, 28) are provided vertically in a top wall (3a) and bottom wall (3b) of said clamp housing (3), said anti-interference grooves (30) are provided to be vertically through the upper peripheral wall section (20a) and lower peripheral wall section (20b) so as to dispose said spring holding pin (25) vertically and said bolt holes (38) for the front fastening bolts to be disposed on both, right and left, sides of said spring holding pin (25). A hydraulic clamp with a swinging clamp arm according to claim 1, characterised in that as clamp housing (103) is formed prolonged sideways, a plurality of clamp arms (104) are arranged properly spaced in the front part of said clamp housing (103) and hydraulic cylinders (105) corresponding thereto are provided in the rear part thereof.

Inventors: MIYATA, ICHIRO
Applicants: KABUSHIKI KAISHA KOSMEK
Application year: 1987
Main classification: B23Q3
IPC codes: B25B5