SLIDE STROKE VARIABLE DEVICE FOR A PRESS

Abstract: A slide is moved up and down by a connecting rod provided at a crankshaft and imparted with long and short strokes by changing over from engagement to disengagement, and vice versa, between an eccentric shaft formed on the crankshaft and an eccentric sheave incorporated with the eccentric shaft. The eccentric sheave is arranged to be downwardly eccentric when the crankshaft is at the bottom dead center, and in this condition, a main cylinder extends through the eccentric shaft, the eccentric sheave and the connecting rod. The main cylinder has a lock pin for connecting the eccentric sheave to the eccentric shaft at its upper limit and to the connecting rod at its lower limit. Movement of the lock pin in the main cylinder causes the eccentric sheave to engage with or disengage from the eccentric shaft. To stop the slide exactly at a predetermined position, provided are a main gearwheel mounted to the crankshaft, knock blocks symmetrically disposed at the periphery of the main gearwheel and air cylinders corresponding to the knock blocks and having piston rods. Adjustment is made to mounting positions of the knock blocks and strokes of the piston rods so as to stop the crankshaft at a predetermined angle when the piston rods of the air cylinders engage with the knock blocks, facilitating the movement of the lock pin.

Description: Detailed Description of the Invention The present invention relates to a slide stroke variable device for a press. The stroke of a slide is a distance of slide movement from a top dead center to a bottom dead center, and fixes maximum height or length of an article to be processed. Namely, maximum depth of drawing is determined in case of drawing process, maximum height in case of a container edge turning process, and maximum length of an article in case of backward extrusion process. Some crankshafts have been developed for use for variable stroke, and prior art is known as described in "Press Binran (Press Handbook)" issued by Maruzen Kabushiki Kaisha of Nihombashi, Chuo-ku, Tokyo, Japan on October 30, 1967, Pages 261 - 262, Fig. 3.26 (W), (X),(Y) and (Z). Any of these known crankshafts utilizes double eccentricity and causes phased changes in slide stroke between the two eccentricities added and subtracted. The crankshafts as disclosed in (W) and (X) are of the type of fixing the outer eccentric sheave by a cylindrical key after adjustment, and those as disclosed in (Y) and (Z) are of the type of fixing by radial engagement. Figs. 6A and 6B illustrate typical structures of prior art crankshafts as described in the above-mentioned publication and as shown in Fig. 3.26 (W). In adjustment of stroke, a setscrew fastening a key (k) is first loosened and the key (k) is rotated by inserting a rod, etc. into a rotation hole, so as to disengage the key (k) from a groove (g) in an outer eccentric sheave (P). Next, the outer eccentric sheave (P) is rotated with use of a rod inserted in a hole (h) so as to engage the key (k) with other groove (g). Although the above-described structures are advantageous in that they can make phased changes in stroke, they require much trouble to adjust the stroke and fail to change the stroke immediately. Accordingly, it is an object of the present invention to solve the above-described problems and to provide a device for adjusting the slide movement so as to have two types of strokes, namely long and short strokes, by incorporating an eccentric sheave with an eccentric shaft formed on a crankshaft and changing over from engagement to disengagement, and vice versa, of the eccentric sheave relative to the eccentric shaft. Although the stroke of the present device is limited to two types, the device can make such change-over without moving the crankshaft and the eccentric sheave. The present invention is characterized in that the eccentric sheave is interposed between the eccentric shaft formed on the crankshaft and the connecting rod mounted on the outer side of said ecentric shaft, and various members are arranged so that the eccentric sheave is downwardly eccentric when the crankshaft is at the bottom dead center, in which condition a cylinder bore is provided passing through the eccentric shaft, the eccentric member and the connecting rod and the cylinder has therein a slidable lock pin which is adapted to connect the eccentric sheave to the eccentric shaft when it is at its upper limit and connect the eccentric sheave to the connecting rod when at its lower limit. The present invention makes it possible to change the slide stroke from a long one to a short one, and vice versa, by providing the eccentric sheave between the eccentric shaft and the connecting rod, and selecting whether the eccentric sheave is to be a part of the eccentric shaft or the connecting rod. The present invention is advantageous in that it causes no change in the position of the bottom dead center and keeps die height constant due to the slide stroke adjustment being made with the crankshaft at the bottom dead center. By the way, the lock pin according to the present invention operates as a means for changing the slide stroke, but such operation makes it a condition that the slide stops at a fixed position. By stopping the slide exactly at a predetermined position such as crank angle 0 degree (top dead center), 180 degrees (bottom dead center), etc., it is possible to decide on operational positions of feed bars relative to positions of the slide in case of a transfer press. Further, it is necessary to set the slide stop posi­ tion exactly in case of a quick-return device being incorporated in the slide driving mechanism. In the present invention, the lock pin for changing the slide strokes is disposed slidably only when the crank angle is 180 degrees, and accordingly, it is required to stop the slide at crank angle 180 degrees to vary the slide stroke. The press brake is to make press operation reliable and safe. As trouble with the brake brings about a serious accident, no device for correcting the stop position of the slide has been developed, although there is a known emergency stop device for a press adapted to operate, for example, when the slide passes the stop position. Fig. 1 is a side view of the slide stroke variable device according to the present invention; Fig. 2 is a sectional view taken on line A-A of Fig. 1; Fig. 3 is a sectional view of a press crown portion showing a slide stop position correcting device for the press having the slide stroke variable device; Fig. 4 is a front view thereof; Fig. 5 is a sectional view taken on line B-B of Fig. 3; and Figs. 6A and 6B show slide stroke variable devices of prior art, Fig. 6A being a sectional view and Fig. 6B being a sectional view taken on line a-a thereof. The preferred embodiments of the present invention will be described hereinbelow with reference to the drawings. A crankshaft 1 is formed with an eccentric shaft 2, which has an eccentric sheave 3 rotatably mounted on the outer circumference thereof. A connecting rod 4 is also rotatably mounted on the outer circumference of the eccentric sheave 3 and is arranged so that the center of the hole therein corresponds to the center of the outer diameter of the eccentric sheave 3. Further, the various members are arranged so that the eccentric sheave 3 is eccentric in the downward direction when the crankshaft 1 is at the bottom dead center. In the above-described assembled condition, a cylinder bore 5 is provided extending through the eccentric shaft 2, the eccentric sheave 3 and the connecting rod 4. The cylinder bore 5 has therein a slidable lock pin 6 and upper and lower pistons 7 and 8 which are disposed therein on and under the lock pin 6, respectively, in superposed condition. The lock pin 6 is pushed upward by the lower piston 8 to reach the upper limit, whereby it connects the eccentric shaft 2 to the eccentric sheave 3, as shown in the drawings. On the other hand, when the lock pin 6 is pushed downward by the upper piston 7 to reach the lower limit, it connects the eccentric sheave 3 with the connecting rod 4. In order to drive the upper piston 7, there is provided an auxiliary cylinder bore 9 having a smaller diameter at the upper end portion of the eccentric shaft 2 and the eccentric sheave 3, with a communication hole 10 communicating the main cylinder bore 5 to the auxiliary cylinder bore 9 which has an auxiliary piston 11 therein. The upper piston 7 is connected to the auxiliary piston 11 by a connection rod 12 inserted in the communication hole 10. A hydraulic passage 13 has an inlet at the axial end of the crankshaft 1 and points toward the comunication hole 10. Oil is supplied from the inlet into the hydraulic passage 13 so as to drive the upper piston 7. For the drive of the lower piston 8, there are provided a plug body 14 at the lower opening of the cylinder bore 5, and a communication rod 15 mounted downwardly to the lower piston 8 and passing through the plug body 14. The cylinder bore 5 is formed with a hydraulic passage 16 through the connecting rod 4, and the lower piston 8 operates by oil supplied from an inlet of the hydraulic passage 16. The crankshaft 1 is mounted via a bearing body 21 to a housing 20 constituting a part of the press crown. The lower end of the connecting rod 4 is formed into an internally threaded sleeve 41, which engages with a connecting screw 42. The connecting screw 42 has a spherical body 43 at the end thereof, and the spherical body 43 is connected to the slide of the press. In the illustrated condition, the lock pin 6 reaches the upper limit with the press at the bottom dead center, locking the eccentric shaft 2 and the eccentric sheave 3. Namely, the eccentric sheave 3 is adapted to rotate as a part of the eccentric shaft 2. In this case, the rotational center of the crank is O₀ and the center of the eccentric pin is O₂ , whereby the stroke has a length of (O₀∼O₂) x 2 and becomes long. When the lock pin 6 is pushed downward by supplying hydraulic pressure through the hydraulic passage 13 and moving the upper piston 7 downward, with the press at the bottom dead center, the lock pin 6 disengages from the eccentric shaft 2 and at the same time is inserted into the connecting rod 4. Accordingly, the eccentric sheave 3 is locked together with the connecting rod 4 and becomes a part thereof. The hole in the eccentric sheave 3 rotates freely from the outer diameter of the eccentric shaft 2. In this case, the rotational center of the crank is O₀ and the center of the eccentric pin is O₁ , whereby the stroke has a length of (O₀∼O₁) x 2 and becomes short. In other words, the stroke in this case corresponds to the stroke of the eccentric shaft itself. The device for correcting the stop position of the press slide will be described. While the embodiment as shown is a press having a quick-return mechanism for slide, it is to be noted that the stop position correcting device of the present invention can be mounted to any type of press. The press having the above-described crankshaft 1 is a double crank press. The crankshaft 1 is mounted to a crown 100, and a slide 101 is connected with the two spherical bodies 43 of the connecting rods 4 and moved up and down by the connecting rod 4 through rotation of the crankshaft 1. At the central portion of the crankshaft 1, namely between the two eccentric shafts 2, there is provided a main gearwheel 102 which is in engagement with a drive pinion 104 provided on a drive shaft 103. The main gear­ sheel 102 is formed as a hollow structure and provided with a slide quick-return mechanism 105 therein. The quick-return mechanism 105 includes an eccentric structure 106 provided at the center of the main gearwheel 102, and a link 107 connecting by pins 108 and 109 the eccentric structure 106 to an eccentric position near the periphery of the main gearwheel 102. When the rotation of the drive pinion 104 causes the main gearwheel 102 to rotate, the crankshaft 1 imparts a quick-return up-and-down movement to the slide 102. Further the drive shaft 103 for the drive pinion 104 has one end thereof protruding from a unit casing, at which end there is provided a clutch unit 110 including a flywheel , and at the other end is a brake unit 111. The flywheel is provided for driving the press. The main gearwheel 102 comprises two-part pan-like members 112 connected together and teeth 113 which are not formed on the connected portion. The connection is formed on an annular bottom portion 114. The drive pinion 104 has two series of teeth 115 so that they engage with the teeth 113 formed on the main gearwheel 102. The crown 100 is provided with air cylinders 116 which are perpendicular to the rotational axis of the main gearwheel 102 and positioned at the outer diameter thereof. Piston rods 117 protrude toward the bottom portion 114 of the main gearwheel 102, and are adapted to engage with knock blocks 118 that are provided at the bottom portion 114 at an angle of 180 degrees. The main gearwheel 102 having the teeth 113 thereon is formed into two parts, the connection therebetween being formed as the bottom portion 114, to which the knock blocks 118 are fastened by setscrews 119. The piston rods 117 of the air cylinders 116 are adjusted to have such length as to set the main gearwheel 102 to a particular angle of the crankshaft, for example the bottom dead center, when the piston rods protrude to the limit (cylinder end) and engage with the knock blocks 118. It is necessary, however, for the piston rods 117 as retracted to be kept away from the main gearwheel 102 so as not to prevent it from rotation. Numeral 120 is an air supply tube connected to the air cylinders 116, 121 an electromagnetic valve for controlling air supply, and 122 an air supply source. During a normal operation of the press, the piston rods 117 of the air cylinders 116 for correcting the stop position are retracted so that they are not in contact with the knock blocks 118 of the main gearwheel 102. In order to stop the press at a desired stop position, for example the bottom dead center, the press is stopped at a predetermined position with use of the clutch and brake of the clutch unit 110 and brake unit 111, and thereafter air is supplied to the air cylinders 116 by taking off the brake and controlling the electromagnetic valve 121, so as to let the piston rods 117 protrude against the knock blocks 118 of the main gearwheel 102. When the main gearwheel 102 fails to reach or overruns the stop position, the slide is adjusted to stop at the desired position when the piston rods 117 are placed in engagement with the knock blocks 118 by contacting first either of the piston rods 117 with one of the knock blocks 118 and rotating the gearwheel 102 slightly. As described above, it is possible to stop the press at the desired position by applying the brakes with the piston rods 117 of the air cylinders 116 being in engagement with the knock blocks 118 of the main gearwheel 102.

Claims: 1. A slide stroke variable device for a press having an eccentric shaft (2) formed on a crankshaft (1) and an eccentric sheave (3) incorporated with said eccentric shaft (2), and having a slide (101) adapted to move up and down by a connecting rod (4) provided on the crank­ shaft (1), said slide (101) being imparted with long and short strokes by changing over from engagement to dis­ engagement, and vice versa, between the eccentric shaft (1) and the eccentric sheave (3), the device comprising: the eccentric sheave (3) arranged so that it is downwardly eccentric when the crankshaft (1) is at the bottom dead center; a main cylinder bore (5) extending through the eccentric shaft (2), the eccentric sheave (3) and the connecting rod (4) in the above arrangement; a lock pin (6) housed in said main cylinder bore (5) for connecting the eccentric sheave (3) to the eccentric shaft (2) when it is at the upper limit and connecting the eccentric sheave (3) to the connecting rod (4) when at the lower limit; and a hydraulic drive mechanism (8) for sliding the lock pin (6) within the main cylinder bore (5). 2. A slide stroke variable device for a press as claimed in Claim 1 wherein said main cylinder bore (5) having the lock pin (6) is provided therein with upper and lower pistons (7, 8) relative to the lock pin (16) in superposed condition, an auxiliary cylinder bore (9) being provided above the main cylinder bore (5) and having therein an auxiliarly piston (11) connected to the upper piston (7) via a connection rod (12), a hydraulic passage (13) being connected at a position where the auxiliary piston (11) operates upward in the auxiliary cylinder bore (9), and another hydraulic passage (16) being connected at a position where the lower piston (8) operates upward in the main cylinder bore (5). 3. A slide stroke variable device for a press as claimed in Claim 2 wherein said auxiliary cylinder bore (9) is provided at an upper end portion of the eccentric shaft (2) and the eccentric sheave (3), and connects said eccentric shaft (2) to said eccentric sheave (3) when the lock pin (6) reaches the upper limit. 4. A slide stroke variable device for a press as claimed in Claim 2 or 3 wherein said main cylinder bore (5) is provided at the lower opening thereof with a plug body (14), through which passes a communication rod (15) connected downwardly to the lower piston (8). 5. An auxiliary stop position correcting device for stopping the slide (101) of a press exactly at a pre­ determined position, comprising a main gearwheel (102) provided at a crankshaft (1), knock blocks (118) sym­ metrically disposed at the periphery of said main gear­ wheel (102), and air cylinders (116) corresponding to said knock blocks (118) and having piston rods (117), wherein adjustment is made to mounting positions of said knock blocks (118) and strokes of said knock blocks (118) and strokes of said piston rods (117) so as to stop the crankshaft (1) at a predetermined angle when the piston rods (117) of the respective air cylinders (116) engage with the knock blocks (118).

Inventors: SHIGA, MASAKATSU, SUGAWARA, MASAYOSHI
Applicants: AIDA ENGINEERING LTD.
Application year: 1987
Main classification: B30B1
IPC codes: B30B15, B30B1