Apparatus for adjusting slide stroke of press.

BACKGROUND OF THE INVENTION

Field of the Invention

0001The present invention relates to an apparatus for adjusting the slide stroke distance of a press (the distance will hereinafter be referred to as "the slide stroke" unless otherwise specified).

Description of the Related Art

0002The pressing speed (N) and the slide stroke (S) of a press have an interrelationship such as that shown in Fig. 8. Such interrelationship is determined, by the pressing structure of a particular press, as an inherent characteristic (S/N ratio) thereof. Accordingly, if the S/N ratio is adjusted, it is possible to selectively effect, with a single press, various operation manners related to producibility and working precision.

0003For this purpose, an apparatus for adjusting slide stroke is used. A general construction of such an apparatus is shown in Fig. 9.

0004Referring to Fig. 9, a crankshaft 10 includes an eccentric portion 11 having an eccentricity amount of e1. An eccentric sheave 20 is fitted on the eccentric portion 11, and has an eccentricity amount of e2 with respect to the axis Z2 of the eccentric portion 11. Thus, a multieccentric structure is formed. A connecting rod (hereinafter abbreviated to "the con'rod") 3 has an upper end portion 3U fitted on the eccentric sheave 20, and a lower end portion swingably supported by a slide 1.

0005With this construction, when the relative position of the eccentric portion 11 and the eccentric sheave 20 in the direction of rotation thereof, that is, the direction of their eccentricity, is changed, it is possible to freely switch the composite amount of eccentricity with respect to the axis Z1 of the crank shaft 10 to a value within the range from (√<maths id="math0001"><math display="inline"><mrow><mover accent="true"><mrow><mtext>(e1 - e2)²</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0547351A2_D0001.tif" /></maths> to (e1 + e2), so as to adjust the stroke of the slide 1.

0006Art concerning apparatuses for adjusting the slide stroke is known, for example, from Japanese Patent Publication No. 48-4356, Japanese Patent Publication No. 51-12150, Japanese Utility Model Publication No. 55-13039, U.S. Patent No. 4,033,252 and German Patent No. 3112382.

0007With such conventional art, the construction is complicated, and the component parts have large diameters or large dimensions irrespective of the slide stroke distance. Furthermore, when the slide stroke distance is adjusted, the relationship between the rotational angle of the crankshaft (i.e., the crank angle) and the slide motion changes. This is disadvantageous to the press which is used in association with various equipment, and also disadvantageous in that the die height changes as well.

0008A slide stroke adjusting apparatus having a built-in switching mechanism of the two-stage switching type, which has small diameters and dimensions and which is capable of maintaining the die height and the slide motion even when the direction of eccentricity is switched, is known from Japanese Utility Model Publication No. 3-53827 (U.S. Patent No. 4,846,014, European Patent No. 0 250 871). A slide stroke adjusting apparatus having an external switching mechanism is known from Japanese Patent Laid-Open No. 4-105800.

0009Recently, however, there are stronger demands for improvements in facility economy, increases in working precision, and decreases in three-dimensional size. Even with the above-described apparatuses, it is sometimes impossible to sufficiently meet these demands.

0010Specifically, with an apparatus having a built-in switching mechanism, since a cylinder device having upper and lower pistons is fitted in a through hole which is formed in communication with all three of the eccentric portion, the eccentric sheave and the con'rod and concentrically with the same axis, this construction requires a large number of component parts, and is thus expensive. In addition, the construction requires complicated and very precise machining and assembly. Further, the replacement of the pistons, packings, etc. is a laborious operation.

0011With an apparatus having an external switching mechanism, since it is necessary to provide a space for allowing the eccentric bush to move in the axial direction of the crankshaft, reductions in size cannot be easily achieved in a narrow interior of the crown. Further, since the rotation gap of the crankshaft bearing makes it essential to provide a gear backlash, the demands for higher precision cannot be easily met.

SUMMARY OF THE INVENTION

0012An object of the present invention is to provide an apparatus for adjusting the slide stroke of a press, the apparatus being capable of easily and quickly switching the slide stroke without causing changes in the die height and the slide motion.

0013Another object of the present invention is to provide an apparatus for adjusting the slide stroke of a press, the apparatus being capable of reducing the size and increasing the rotational speed while assuring a predetermined composite eccentricity amount.

0014According to one form of the present invention, there is provided an apparatus for adjusting the slide stroke of a press, the apparatus adjusting the slide stroke by changing the direction in which an eccentric portion of a crankshaft and an eccentric sheave interposed between the crankshaft and a con'rod are eccentric. The apparatus is characterized in that it comprises: holes having axes intersecting the axis of a crankshaft, the holes being formed in an eccentric portion of the crankshaft, an eccentric sheave and a con'rod, the eccentric portion and the eccentric sheave being disposed in such a manner as to be eccentric in the same direction, the holes being combined in such a manner that those holes formed in the eccentric portion and the eccentric sheave are coaxial with a common axis of the above associated members and those holes formed in the con'rod and the eccentric sheave are coaxial with another common axis of the above associated members; first lock pins received in the hole of the eccentric portion; first projection and retraction switching means for projecting and retracting the first lock pins into and from the corresponding holes of the eccentric sheave; switching force transmitting means for applying a switching force to the first projection and retraction switching means through an interior of the crankshaft; second lock pins received in the hole of the con'rod; and second projection and retraction switching means for projecting and retracting the second lock pins into and from the corresponding hole of the eccentric sheave.

0015In this form of the present invention, a switching force applied from the outside of the crankshaft is transmitted through the switching force transmitting means disposed in the crankshaft to the first projection and retraction switching means, whereby the first projection and retraction switching means is suitably operated to project the first lock pins into the corresponding holes of the eccentric sheave. After this projection, the second projection and retraction switching means is either manually or automatically operated to draw the second lock pins received in the hole of the con'rod from the corresponding hole of the eccentric sheave.

0016As a result, the eccentric sheave, which has been integral with the con'rod is shifted to a state of being integral with and fixed to the crankshaft without causing any changes in the relative position of the con'rod, the eccentric sheave and the crankshaft in the direction of rotation. In other words, the slide stroke can be switched without causing a change in the die height.

0017When the eccentric sheave is to be shifted from a state of being integral with the crankshaft to a state of being integral with the con'rod, the second projection and retraction switching means and the first projection and retraction switching means are operated in this order in an opposite manner to the above manner.

0018With this form of the present invention, since the side of the crankshaft is provided with first lock pins, first projection and retraction switching means for projecting and retracting the first lock pins and a switching force transmitting means disposed in the crankshaft, while the side of the con'rod is provided with second lock pins and second projecting and retracting switching means for projecting and retracting the second lock pins, it is possible to switch the composite amount of eccentricity without changing the position of the eccentric sheave. Thus, it is possible to provide an apparatus for adjusting the slide stroke of a press, the apparatus being capable of quickly and reliably switching the slide stroke without causing changes in the die height, and is also capable of being handled easily and produced at low cost.

0019Another form of the present invention is based on the following point: In an arm-type crank structure, since the distance between the points of support of the journal is increased by the thickness of the arms, the journal (crankshaft) diameter is inevitably greater than that of a full-eccentric-type crank structure. However, even in the case of an arm-type crank structure, if a certain eccentric sheave is fitted on a crank-pin portion between arm portions, this arrangement provides a greater advantage (i.e., a reduction in size and an increase in rotational speed) than disadvantage (i.e., an increase in the journal diameter). Thus, the second form of the present invention is characterized in that an arm-type crank structure includes a divided eccentric sheave and a ring member.

0020Specifically, the second form of the present invention is characterized in that, in a slide drive of a double-eccentric structure which has first and second eccentric sections eccentric with respect to the central axis of a crankshaft and which is able to vertically drive a slide through a con'rod, a first eccentric section comprises a crank-pin portion provided between a pair of arm portions of a crankshaft, and a second eccentric section comprises an eccentric sheave capable of fitting on the crank-pin portion and a ring member capable of fitting on the eccentric sheave. The eccentric sheave comprises a divided structure which can be fitted onto the crank-pin portion from the radial direction thereof.

0021In this form of the present invention, the divided eccentric sheave is brought close to and fitted on the crank-pin portion from the radial direction thereof while the crank-pin portion, forming the first eccentric section, and the eccentric sheave, forming the second eccentric section, are being held at a relative position at which the composite eccentric amount of these members is minimum. Thereafter, the ring member is slid in the axial direction of the crankshaft and fitted on the eccentric sheave, so that the eccentric sheave is integrally fixed in place. As a result, it is possible to achieve a reduction in the size and an increase in the rotational speed of the entire system while assuring the same maximum value of composite eccentric amount as that in a conventional full-eccentric-type double-eccentric structure.

0022In brief, with the second form of the present invention, a crank-pin portion in a double-arm-type crank structure constitutes a first eccentric section, and a divided eccentric sheave is fitted on the first eccentric section from the radial direction and integrated by means of a ring member. Thus, the eccentric sheave can be easily and securely mounted on the inter-arm first eccentric portion. Since the outer diameter at the eccentric sheave can be reduced, it is possible to achieve both a reduction in the size and an increase in the rotational speed of the entire system.

BRIEF DESCRIPTION OF THE DRAWINGS

0023<ul id="ul0001" list-style="none"><li>Fig. 1 is a longitudinal sectional view of the entire construction of an apparatus according to the present invention, the apparatus being shown in its assembled state;</li><li>Fig. 2 is a sectional view of the apparatus, taken along a plane perpendicular to the surface of Fig. 1;</li><li>Fig. 3 is an exploded perspective view for explaining first projection and retraction switching means;</li><li>Figs. 4A and 4B are views for explaining the operation of the first projection and retraction switching means and a switching force transmitting means;</li><li>Fig. 5 is a longitudinal sectional view of the entire construction of another apparatus according to the present invention, the apparatus being shown in its assembled state;</li><li>Fig. 6 is a longitudinal sectional view of the apparatus shown in Fig. 5, for explaining the manner of assembling the apparatus;</li><li>Fig. 7 is a sectional view taken along the line A-A shown in Fig. 6;</li><li>Fig. 8 is a graph for explaining the slide stroke and the pressing speed;</li><li>Fig. 9 is an explanatory view showing the construction of a conventional apparatus; and</li><li>Fig. 10 is a longitudinal sectional view of another conventional apparatus.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0024Figs. 1 to 4 show one form of the present invention.

0025As shown in Figs. 1 and 2, an eccentric portion 11 of a crankshaft 10 and an eccentric sheave 20 are disposed in such a manner that they are eccentric in the same direction with the amount of their eccentricity increasing toward the lowermost position (as viewed in Figs. 1 and 2) where that amount reaches the maximum.

0026The eccentric portion 11 and the eccentric sheave 20 are formed with a combination of holes, namely, an eccentric-portion vertical hole 11V and an eccentric-sheave first hole 21, which are both coaxial with a vertical axis (a first common axis Y1) intersecting the axis Z1 of the crankshaft 10. On the other hand, an upper end portion 3U of a con'rod 3 and the eccentric sheave 20 are formed with another combination of holes, namely, a con'rod vertical hole 4 and the eccentric-sheave first hole 21, which are both coaxial with another vertical axis (a second common axis Y2) intersecting the axis Z1 of the crankshaft 10.

0027Although in the illustrated example, the vertical axes Y1 and Y2 are of the same line, and the eccentric-sheave first hole 21 serves as both the eccentric-sheave hole combined with the vertical hole 11V of the eccentric portion 11 and the eccentric-sheave hole combined with the vertical hole 4 of the con'rod 3, this is a mere example, and the present invention is not intended to be limited thereto. For example, the vertical axis Y2 may be inclined by a desired angle to the left or right, as viewed in Fig. 2. Thus, an eccentric-sheave first hole 21 corresponding to the eccentric-portion vertical hole 11V and that corresponding to the con'rod vertical hole 4 may be formed separately.

0028The vertical hole 11V of the eccentric portion 11 receives a lock pin 12 capable of moving in the vertical hole 11V in the direction of the vertical axis Y1, and capable of projecting into and retracting from the corresponding first hole 21 of the eccentric sheave 20.

0029When the lock pin 12 is projected into the corresponding first hole 21 of the eccentric sheave 20, the eccentric sheave 20 becomes locked to the eccentric portion 11 of the crankshaft 10. In this condition, since the direction of eccentricity is set as shown in Figs. 1 and 2, the amount of composite eccentricity is expressed as the sum of the amount of eccentricity of the eccentric portion 11 and that of the eccentric sheave 20. Referring to Fig. 9, the sum is expressed as (e1 + e2) where e1 represents the eccentricity amount of the eccentric portion 11 and e2 represents that of the eccentric sheave 20.

0030The rotational power of the cranshaft 10 is to be transmitted to the con'rod 3 through the eccentric portion 11 and the eccentric sheave 20 integral therewith.

0031In view of this fact, the embodiment includes another lock pin 16 received in the vertical hole 11V of the eccentric portion 11, and a second hole 23 formed in the eccentric sheave 20 at a position corresponding to the lock pin 16. The pair of lock pins 12 and 16 constitute first lock pins, which allow the eccentric sheave 20 to be very securely locked to the eccentric portion 11.

0032The first lock pins comprising the pair of lock pins 12 and 16 are so configured as to be combinable with first projection and retraction switching means 40. As shown in detail in Figs. 3 and 4, each of the lock pins 12 and 16 has an end portion to serve as an inward end portion. A part of each end portion corresponding to approximately 3/4 of the circumference thereof is cut off so that the lock pins 12 and 16 can overlap each other within a region at the same level.

0033Specifically, each end portion of the lock pin 12 (16) is formed with a notch space 15 (19) by cutting off a part of the end portion corresponding to approximately 3/4 thereof, the remaining part that corresponds to approximately 1/4 of the end portion constituting a projection 13 (17) of the lock pin 12 (16). The notch space 15 (19), partly defined by the projection 13 (17) of the lock pin 12 (16), is able to receive the projection 17 (13) of the other lock pin 16 (12). The projection 13 (17) of the lock pin 12 (16) is formed with a transverse groove 14 (18) to extend perpendicularly to the axis of the vertical hole 11V of the eccentric portion 11.

0034The transverse groove 14 (18) is able to receive a cam pin 42 (41) constituting a part of the first projection and retraction switching means 40. These cam pins 42 and 21 are attached to the forward (inward) end of a rotary member 30.

0035With the above configuration, when the rotary member 30 is rotated by approximately 140° in the counter-clockwise direction, as viewed in Fig. 4A, the first lock pins 12 and 16 move away from each other, that is, outward, as indicated by the associated arrows in Fig. 4B, so that the outward, or forward, end portions 12F and 16F of the first lock pins 12 and 16 are moved from the position shown in Fig. 1 to simultaneously enter the corresponding holes 21 and 23, respectively, of the eccentric sheave 20. This operation enables, together with the operation of second projection and retraction switching means described later, the eccentric sheave 20 to be shifted from a state of being fixed to the con'rod 3 to a state of being fixed to the eccentric portion 11.

0036The rotary member 30 constitutes a switching force transmitting means. As shown in Fig. 1, the rotary member 30 is rotatably fitted in a horizontal hole 11H formed in the crankshaft 10 about the axis 21 of the crankshaft 10, and is capable of transmitting a switching force (rotative force), applied to an outer shaft portion 31 of the rotary member, to the first projection and retraction switching means 40 (i.e., 41 and 42) through an interior of the crankshaft 10.

0037The rotary position of the rotary member 30 indicates which of the shifted position the eccentric assumes, that is, whether the eccentric sheave 20 is locked to the eccentric portion 11 or the con'rod 3. The rotational position of rotary member 30 is detected by using a detection member 32 mounted on the outer shaft portion 31 and a first position detecting sensor 33 mounted to the stationary side.

0038The rotary member 30 is confined to or released from its rotational position by using fixing means and pressure media. In this example of the embodiment, the fixing means includes an ETP bush 35 (produced by Miki Pulley Kabushiki Kaisha) and a pressure screw (not shown). The pressure screw is operated suitably to cause the rotary member 30 to be fastened with or relieved from a friction force exerted by pressure media, including the bush 35, between an outer peripheral surface 31A of the outer shaft portion 31 of the rotary member 30 and an inner peripheral surface 36A of a flange 36 integrated with the crankshaft 10, whereby the rotary member 30 is confined or released.

0039A pair of lock pins 5, together constituting second lock pins, are received in the vertical hole 4 of the con'rod 3 at the upper end portion 3U thereof in such a manner that the second lock pins 5 are movable along the vertical axis (second common axis) Y2. The lock pins 5 have forward, or inward, end portions formed as tapered portions 6 tapered downward, as viewed in Fig. 1, and engageable with a similarly tapered portion 22 of the corresponding first hole 21 of the eccentric sheave 20. When the second lock pins 5 are pushed downward, that is, toward the press load application side, the tapered portions 6 are brought into engagement with tapered portions 22, thereby locking the eccentric sheave 20 to the con'rod 3.

0040The tapered portions 6 and 22 are formed in order to securely link the eccentric sheave 20 to the con'rod 3 without involving any play in the direction toward the press load application side.

0041When the eccentric sheave 20 is fixed to the con'rod 3, the eccentric sheave 20 moves together with the upper end portion 3U of the con'rod 3 At this time, since the eccentric sheave 20 needs to provide only a very small action of transmitting the rotational power of the crankshaft 10 (i.e., bear only a small load transmission torque), a high level of precision of a pressing operation can be more positively assured.

0042Second projection and retraction switching means 50 comprises a cylinder device 51 having piston rods 52 connected to the second lock pins 5. The entire means 50 is secured to an outer side of the upper end portion 3U of the con'rod 3 by a bolt 53, as shown in Fig. 2.

0043Pushing the piston rods 52 downward causes the eccentric sheave 20 to be locked to the con'rod 3 by the second lock pins 5, whereas drawing the piston rods 52 upward causes the eccentric sheave 20 to be released from that locked state. The position of the second lock pins 5 is detected by a second position detecting sensor having elements 55H and 55L facing the vertical hole 4 of the con'rod 3.

0044A bush 7 is fitted on the inner periphery of the eccentric sheave 20, while a bush 8 is fitted on the inner periphery of the upper end portion 3U of the con'rod 3.

(Integrating the Eccentric Sheave with Eccentric Portion)

0045Before the integrating operation, the second lock pins 5 are in their position of being projected in the first hole 21 of the eccentric sheave 20 (this position of the lock pins 5 is represented by the lock pin 5 shown on the left side of the vertical line Y2 in Figs. 1 and 2). When the first lock pins 5 are in the above-described projected position, the first lock pins 12 and 16 are in their retracted position corresponding to the position shown in Fig. 4A.

0046In the integrating operation, a rotative force, acting in a certain direction, is applied from the outside of the crankshaft 10 to the outer shaft portion 31 of the rotary member 30 so that the rotary member 30, serving as the switching force transmitting means, rotates in the counter-clockwise direction, as viewed in Fig. 2 and Fig. 4A.

0047As the rotary member 30 rotates, the cam pins 42 and 41, serving as the first projection and retraction switching means, respectively cause the first lock pin 12 and 16 to move outward away from each other, as indicated by the associated arrows in Fig. 4B. As a result, the forward end portion 12F of the first lock pin 12 enters the corresponding first hole 21 of the eccentric sheave 20, and the forward end portion 16F of the other first lock pin 16 enters the corresponding second hole 23 of the eccentric sheave 20, whereby the eccentric sheave 20 becomes locked to the eccentric portion 11.

0048When the first position detecting sensor 33 has detected the resultant change in the rotational position of the rotary member 30, the second projection and retraction switching means 50 effects a releasing action, whereby the second lock pins 5 are drawn upward, and thus brought from the projected position (represented by the lock pin 5 shown on the left side of the vertical axis Y2 in Figs. 1 and 2) to the retracted position (represented by the lock pin 5 shown on the right side of the vertical axis Y2 in these figures).

0049The eccentric sheave 20 is now completely shifted to the position of being fixed to the eccentric portion 11 by the first lock pins 12 and 16. In this state, the eccentric sheave 20 is capable of bearing a great load transmission torque, and allowing the con'rod 3 to perform smooth swinging and reciprocating motion.

0050In this condition, the composite eccentricity amount equals the sum (e1 + e2) at maximum. As a result, the manner of operation effected has a great slide stroke and a low number of strokes per minute (SPM), with each sliding action taking place in accordance with the outer, large-diameter contour of the eccentric sheave 20. The operation can be performed with efficient SN and PV values.

(Integrating the Eccentric Sheave to the Con'rod)

0051In this integrating operation, the piston rods 52 of the second projection and retraction switching means 50 presses the second lock pins 5 downward so that the second lock pins 5 are brought from the retracted position (shown on the right side of the vertical line Y2 in Figs. 1 and 2) to the projected position (shown on the left side of the same). As a result, the eccentric sheave 20 is locked to, and thus integrated with, the con'rod 3 with the tapered portions 6 of the second lock pins 5 pressing downward (toward the press load application side) against the tapered portions 22 of the corresponding first hole 21 of the eccentric sheave 20. The resultant change in the position of the second lock pins 5 is detected by the second position detecting sensor element 55L.

0052Thereafter, the rotary member 30 (the switching force transmitting means) is rotated in the opposite direction to the direction in the above operation, that is, in the clockwise direction, as viewed in Fig. 4B, whereby the cam pins 41, 42 (the first projection and retraction switching means 40) are brought to the position before the current integrating operation, as shown in Fig. 1. This operation causes the first lock pins 12 and 16 to be retracted from the corresponding holes, that is, the first and second holes 21 and 23, respectively, of the eccentric sheave 20.

0053The eccentric sheave 20 is now completely integrated with the con'rod 3 by virtue of the locking of the second lock pins 5 without any play in the direction toward the press load application side. In this condition, the composite eccentricity amount equals the eccentricity amount e1 of the eccentric portion 11 per se, thus achieving the minimum eccentricity amount of the system. Accordingly, the manner of operation provided has a small slide stroke and a high SPM.level.

0054At this time, the eccentric sheave 20, whose small-diameter inner periphery slides on the outer side (7) of the eccentric portion 11, needs to bear only a small load transmission torque, and the operation can be performed with efficient SN and PV values.

0055Thus, in the above-described embodiment, the eccentric portion 11 and the eccentric sheave 20 are disposed in such a manner as to be eccentric in the same direction, the eccentric-portion vertical hole 11V is provided to establish link between the eccentric portion 11 and the eccentric sheave 20, the con'rod vertical hole 4 and the eccentric-sheave first hole 21 are provided to establish link between the con'rod 3 and the eccentric sheave 20, the side of the eccentric portion 11 is provided with the first projection and retracting switching means 40 for projecting and retracting the first lock pins 12 and 16 as well as the switching force transmitting means 30, and the side of the con'rod 3 is provided with the second projection and retraction switching means 50 for projecting and retracting the second lock pins 5. Therefore, the slide stroke can be quickly and easily switched in two stages without changing the die height.

0056In the illustrated example of the embodiment, the vertical hole 11V of the eccentric portion 11 and the first hole 21 of the eccentric sheave 20, which holes are for projection and retraction of the first lock pins 12 and 16 from the former to the latter and vice versa, are formed coaxially with the vertical axis Y1 common to the above members 11 and 20, while the vertical hole 4 of the con'rod 3 and the first hole 21 of the eccentric sheave 20, which holes are for projection and retraction of the second lock pins 5 from the former to the latter and vice versa, are formed coaxially with the vertical axis Y2 common to the above members 3 and 20. This arrangement is advantageous in that the construction is simple, thereby enabling a great reduction in production costs. Further, the operation of replacing packings, etc. is not necessary, thereby enabling the apparatus to be easily handled.

0057The first projection and retraction switching means 40 has an opposing-pin structure capable of simultaneously switching the position of the pair of first lock pins 12 and 16, thereby enabling quick and reliable switching operations. Furthermore, the switching enables the eccentric sheave 20 to be securely fixed to the eccentric portion 11 in such a manner to be able to bear a great load transmission torque. The switching force transmitting means 30, which comprises a rotary member 30 passed through the inside of the crankshaft 11, enables a switching operation to be performed from the outside of the crankshaft 10. Thus, the switching mechanism requires a space of a smaller axial dimension than a conventional external-type switching mechanism.

0058The second projection and retraction switching means 50, comprising a cylinder device 51 connected to the second lock pins 5 and integrally secured to an outer side of the the con'rod 3, has only a short stroke for effecting integration and separation of the con'rod 3 with respect to the eccentric sheave 20. This arrangement also serves to enable quick and secure switching.

0059The forward end portions of the second lock pins 5 have tapered portions 6, while the corresponding first hole 21 of the eccentric sheave 20 has a tapered portion 22 at the end confronting the lock pins 5. This arrangement enables a secure link between the the con'rod 3 and the eccentric sheave 2, in which these members are pushed toward the press load application side in such a manner as to eliminate play in this direction. Thus, it is possible to perform a pressing operation with a high level of precision.

0060An operation of switching the slide stroke is performed in a condition in which the eccentric sheave 20 is locked to either the eccentric portion 11 or the con'rod 3 by either the first lock pin 12 (16) or the second lock pins 5. Thus, even in a switching operation, the eccentric sheave 20 is not brought to a free state. Accordingly, switching in two stages is possible without entailing a change in the die height.

0061The provision of the position detecting sensors 33, 55L and 55H enables a switching operation to be performed easily and reliably.

0062A second form of the present invention is shown in Figs. 5 through 7.

0063Referring to Fig. 5, a crank structure 100 is a double-arm-type, and comprises a crankshaft 111 having a pair of arms 112 and 113, and a crank-pin portion 114 between the pair of arms 112 and 113. A con'rod 103 is indicated by two-dot-chain lines.

0064The central axis Z2 of the crank-pin portion 114 is eccentric from the central axis Z1 of the cranshaft 111 by an amount e1. Thus, the crank-pin portion 114 constitutes a first eccentric section.

0065An eccentric sheave 120 has a central axis Z3 which is, when the eccentric sheave 120 is fitted on the crank-pin portion 114, as shown in Fig. 5, eccentric from the central axis Z2 of the crank-pin portion 114 by an amount e2. The eccentric sheave 120 constitutes a second eccentric section.

0066In the condition shown in Fig. 5, the first and second eccentric sections are assembled in such a manner that the sum of the amount of eccentricity e1 of the first eccentric section and that e2 of the second eccentric section assumes the maximum value corresponding to the full downward eccentricity. Therefore, the entire double-eccentric structure has the maximum composite eccentricity amount expressed as (e1 + e2).

0067The eccentric sheave 120 has a structure divided into two pieces 120S and 120L, as shown in Figs. 6 and 7, the piece 120L being larger than the other piece 120S. Accordingly, the two pieces 120L and 120S can be brought close to and fitted on the crank-pin portion 114 between the arms 112 and 114 from radial directions of the crank-pin portion 114, as shown in Fig. 5. The eccentric sheave 120 may be alternatively divided into three or more pieces.

0068A ring member 130 serves as a means by which the two pieces of the eccentric shave 120 thus fitted are integrated together. For this purpose, the ring member 130 has an inner diameter slightly smaller than the outer diameter of the eccentric sheave 120.

0069If the respective eccentricity amounts e1 and e2 of the first and second eccentric sections 114 and 120 are the same as those of a full-eccentric-type structure, shown in Fig. 10, the outer diameter D2 at the eccentric sheave 120 carrying the ring member 130 fitted thereon is smaller than the corresponding outer diameter D1 conventionally obtainable. In the illustrated example, <maths id="math0002"><math display="inline"><mrow><mtext>D1 = 1.17 x D2</mtext></mrow></math><img file="EP0547351A2_D0002.tif" /></maths> . In Fig. 5, the outer diameter Dc of the crank-pin portion 114 and the outer diameter dc of the crankshaft (journal) 111 satisfy the relationship of Dc ≧ dc.

0070In the example shown in Fig. 5, the outer diameter dc of the crankshaft (journal) 111 is 1.1 times the corresponding outer diameter de of the structure shown in Fig. 10 (i.e., <maths id="math0003"><math display="inline"><mrow><mtext>dc = 1.1 x de</mtext></mrow></math><img file="EP0547351A2_D0003.tif" /></maths> ). However, the arrangement of the present invention which is directed to decreasing size and increasing rotational speed has much more advantage than disadvantage. That is, the achievement of a reduction in the outer diameter D2 at the eccentric sheave 120 is much more significant than an increase in the outer diameter of the crankshaft (journal) 111.

0071In the condition where the eccentric sheave 120 is fitted on the crank-pin portion 114, the relative position of these members 114 and 120 in the direction of rotation, in other words, the composite eccentricity amount <maths id="math0004"><math display="inline"><mrow><mtext>E [E = f(e1</mtext></mrow></math><img file="EP0547351A2_D0004.tif" /></maths> , <maths id="math0005"><math display="inline"><mrow><mtext>e2)]</mtext></mrow></math><img file="EP0547351A2_D0005.tif" /></maths> with respect to the central axis Z1 of the crankshaft 111 may be adjusted by any known adjusting mechanism. Hence, the illustration of an adjusting mechanism is omitted from Figs. 5 to 7.

(Assembly)

0072First, as shown in Figs. 6 and 7, the crankshaft 111 is held at its bottom dead center position, at which the eccentricity amount e1 of the crank-pin portion 114 is present below the the central axis Z1.

0073Subsequently, the large piece 120L, one of the pieces constituting the eccentric sheave 120, is introduced into the space between the pair of arms 112 and 113 to be brought close to the crank-pin portion 114 from above in a radial direction (the direction indicated by symbol Y1 in Fig. 6), and is fitted on the upper side of the crank-pin 114. Then, the other, or the small, piece 120S is similarly brought close to the crank-pin portion 114 from below (in the direction indicated by symbol Y2 in Fig. 6, and is fitted on the lower side of the crank-pin portion 114.

0074The resultant state of the eccentric sheave 120 is maintained with a suitable tool, etc., and the ring member 130 is slid from the direction X shown in Fig. 6 with the crankshaft 111 passing through the ring member 130, and is fitted on the eccentric sheave 120 (120L and 120S).

0075By this operation, the eccentric sheave 120 is integrally held in position, and properly assembled on the crank-pin portion 114.

0076Thereafter, the relative position of the crank-pin portion 114 constituting the first eccentric section and the eccentric shave 120 constituting the second eccentric section is fixed to a desired position.

0077Specifically, in the condition shown in Fig. 5, if the eccentric sheave 120 (120L and 120S) is fixed to the con'rod 103, the composite eccentric amount equals e1, the minimum, whereas if the eccentric sheave 120 is fixed to the crank-pin portion 114, the composite eccentric amount equals the sum (e1 + e2) the maximum. Thus, the stroke distance of reciprocating motion of the associated slide can be changed.

0078Thereafter, when the crankshaft 111 is rotated in a predetermined direction, the slide reciprocates with a stroke determined by the adjusted composite eccentricity amount.

0079In the above-described embodiment, since the crank-pin portion 114 of the double-arm-type crank structure 100 (111, 112, 113 and 114) constitutes a first eccentric section, and a eccentric sheave 120 divided into pieces is fitted on the first eccentric section from the radial direction and fixed to the crank-pin portion 114 with the pieces of the eccentric sheave 120 being integrated by a ring member 130. Therefore, while the same maximum composite amount of eccentricity (e1 + e2) is assured, the outer diameter D2 at the eccentric sheave can be greatly reduced from the outer diameter D1 conventionally obtainable. For example, the diameter D2 can be reduced to 85 % or less of the conventional value. Accordingly, it is possible to achieve both a reduction in the size of the apparatus and an increase in the rotational speed.

0080Since the crank-pin portion 114 is provided between the pair of arms 112 and 113, the structure has a good mechanical balance, and is able to provide smooth rotational motion. Since the eccentric shave 120 has a divided structure (120L and 120S), it can be fitted in the radial direction through the space between the arms 112 and 113 onto the first eccentric section (114), thereby facilitating assembly.

0081Since the ring member 130 can be fitted on the eccentric shave 120 (120L and 120S) by sliding the ring member 130 in the direction X shown in Fig. 6, the eccentric sheave 120 can be easily and quickly integrated and fixed in position.