Patent Publication Number: US-2013236586-A1

Title: Mechanism and system for clamping

Description:
RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 13/074,232, filed Mar. 29, 2011, which claims the benefit of priority of U.S. Provisional Patent Application No. 61/318,729 filed Mar. 29, 2010, which are both incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present document relates generally to a clamping mechanism. More particularly, the present document relates to a clamping system and mechanism for opening, closing and clamping presses for molding. 
     BACKGROUND 
     Mechanical molding presses are commonplace in the manufacturing industry. In order to lock these presses in position, it is necessary to provide a clamping system or mechanism to keep the parts of the mold in position while plastic or the like is injected under pressure. Often these clamping mechanisms are large and complex and, like many mechanical systems, may require externally applied lubricant to keep moving parts operating smoothly. 
     In some molding applications, additional consideration may need to be given to the loads, space constraints and clean room requirements, for example, if the molding is for medical applications or the like, where the potential for contaminant lubricant leakage is possible. In these environments, conventional hydraulic or toggle clamping mechanisms may not be appropriate. Further, electro-mechanical devices such as servo drives are generally not capable of delivering the repetitive loads and forces often required for plastic molding and typically are quite large and/or produce significant amounts of heat during operation. 
     SUMMARY 
     Thus, there is a need for a clamping apparatus that is simple, and a clamping system with efficient means to open, close and mechanically clamp a molding press. There is a further need for a clamping mechanism and system to be used in a clean-room environment, for injection and compression molding, where it would be advantageous if the clamping system and mechanism used a minimal amount or no external lubrication. 
     In one aspect, there is provided a clamping mechanism including: a drive; a shaft connected to the drive; an eccentric hub that is driven to rotate by the shaft; a fixed support structure that supports the eccentric hub such that the eccentric hub can rotate; and a moving support structure that is connected to the eccentric hub such that the moving support structure is driven substantially linearly based on rotational motion of the eccentric hub and serves to clamp an object between the moving support structure and a fixed structure adjacent to the moving support structure. This clamping mechanism is intended to be simple and operates with little or no external lubricants. 
     In a further aspect, a clamping mechanism is provided wherein the eccentric hub may be driven by a shaft through an angle of less than approximately 180 degrees. The eccentric hub of the clamping mechanism may be driven by the shaft by a drive key connecting the shaft to the eccentric hub. 
     In another aspect, a moving support structure of the clamping mechanism may support a first portion of a mold and the fixed structure adjacent the moving support structure may be a second portion of the mold. In one case, the clamping mechanism may further include a load cell provided to the eccentric hub to monitor the pressure applied. 
     In a further aspect, there is provided a clamping system including: a single drive; a shaft connected to the drive; a plurality of clamping mechanisms, each clamping mechanism comprising: an eccentric hub that is driven to rotate by the shaft; a fixed support structure that supports the eccentric hub such that the eccentric hub can rotate; a moving structure that is connected to the eccentric hub such that the moving support structure is driven substantially linearly based on rotational motion of the eccentric hub wherein the plurality of clamping mechanisms support a platen and the plurality of clamping mechanisms serve to clamp an object between the platen and a fixed structure adjacent to the platen when the eccentric hub is created. 
     In another aspect, a clamping system is provided wherein the eccentric hub of the clamping mechanism may be driven by the shaft through an angle of less than approximately 180 degrees. The clamping system may further have an eccentric hub of a clamping mechanism driven by a shaft by a drive key connecting the shaft to the eccentric hub. 
     In another aspect, a clamping system may further include a moving support structure that may support a first portion of a mold and a fixed structure adjacent to the moving support structure that may be a second portion of the mold. The clamping system may further include a load cell provided to the eccentric hub to monitor the pressure applied. 
     Other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
       Embodiments will now be described, by way of example only, with reference to the attached figures, wherein: 
         FIG. 1  illustrates a clamping system with two clamping mechanisms according to one embodiment; 
         FIG. 2  illustrates the clamping system in use with a molding press; 
         FIG. 3A  illustrates a clamping mechanism is a locked/clamped position; 
         FIG. 3B  illustrates the clamping mechanism in an unlocked/unclamped position; and 
         FIG. 4  illustrates a clamping system in block diagram form. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a clamping system  100  according to an embodiment herein. The clamping system  100  includes at least one clamping mechanism  105  (two are illustrated), a drive shaft  110  interacting with the clamping mechanism  105  to drive the clamping mechanism  105  and a drive (not shown) for driving the drive shaft  110 . In a case where the drive shaft  110  may extend over some distance, the drive shaft  110  may be supported by a spacer  115  and spacer bearing  120 . 
       FIG. 2  shows the use of the clamping system  100  with an injection molding press  200 . The clamping system  100  is provided between a fixed platen  205  and a moving platen  210 . A lower mold portion  215  is mounted on the moving platen  210 . The clamping system  100  can be operated to move the moving platen  210  and lower mold portion  215  up and down in relation to an adjacent upper mold portion (not shown) as shown by arrow  220  in  FIG. 2  and clamp the lower mold portion  215  in place against the upper mold portion. 
       FIGS. 3A and 3B  illustrate the clamping mechanism  105  in clamped and unclamped positions, respectively. The clamping mechanism  105  includes a fixed pillow block  125  to mount the clamping mechanism on the fixed platen  205 . The fixed pillow block  125  supports the drive shaft  110  via a shaft bearing  130 . The drive shaft  110  is keyed to a drive key  135  that supports and drives an eccentric hub  140 . The drive key  135  may be a precision spline between the eccentric hub  140  and shaft  110 , which allows for a direct drive. The eccentric hub  140  is attached to a moving pillow block  145  via a pillow bearing  150  such that the moving pillow block  145  can rotate relative to the eccentric hub  140 . The moving pillow block  145  can then be attached to the moving platen  210 . In some embodiments, a load cell  155  may be provided between the moving pillow block  145  and the moving platen  210 . The eccentric hub  140  is configured such that a rotation of the eccentric hub  140  causes substantially linear movement of the moving pillow block  145  in a vertical direction. 
     Although the present embodiment illustrates vertical movement, it will be understood that there may also be situations involving non-vertical movement in which a similar mechanism may be utilized. Further, other clamping mechanisms that include an eccentric hub that is driven to rotate by a shaft and including a moving support structure such that the moving support structure is driven substantially linearly based on rotational motion of the eccentric hub may be possible. The present disclosure describes a sample embodiment that may be preferred due to its simplicity. 
     In operation, the clamping mechanism  105  is initially in a lowered position as shown in  FIG. 3B . In this lowered position, the eccentric hub  140  is positioned such that the moving pillow block  145  is lowered. The drive shaft  110  then rotates and causes the drive key  135  to drive the eccentric hub  140  to rotate such that the moving pillow block  145  is moved linearly upward by the pillow bearing  150 . The drive shaft  110  continues driving until the moving pillow block  145  and the related lower mold portion  215  is placed with sufficient pressure against the upper mold portion. The drive shaft  110  then maintains the pressure on the moving pillow block  145 . When the axes of the drive shaft  110 , eccentric hub  140  and pillow bearing  150  are substantially aligned normal to the direction of clamp, the clamping mechanism  105  creates a mechanically locked condition, which may be effectively as strong as the compressive structural capabilities of the weakest member of the clamping mechanism  105 . The nature of the elements of the clamping mechanism acting in a single central vector results in a solid mechanical lock condition, which may only be released by rotating the eccentric hub  140 , similar to the locked condition of a human elbow when the arm is fully extended. No other lock element should be necessary; however, the rotation of the drive shaft/eccentric hub may also be locked, if desired, to resist excessive vibration, although this generally would not occur in a rigid/solid press. 
     The eccentric hub  140  and other elements of the clamping mechanism  105  may be formed of steel or other appropriate material to provide sufficient structural strength. 
     The clamping mechanism  105  is somewhat similar to a crankshaft and connecting rod assembly (not shown); however, the eccentric movement of the clamping mechanism  105  will generally not involve a full revolution. The clamping mechanism  105 , and in particular the eccentric hub  140 , may only rotate back and forth about a given angle, and, in one particular case, the angle may be less than 180 degrees. In another case, the angle may be less than approximately 130 degrees. 
     The clamping system  100  may include a single clamping mechanism  105  or may include a plurality of clamping mechanisms  105  (two are shown in  FIG. 1 ). The clamping mechanisms  105  are intended to be positioned normal and opposite the mold portions. 
     The clamping system  100  and clamping mechanism  105  may be harmonically driven and balanced by either a single drive (as indicated in  FIG. 1 ) or a plurality of drives, although the use of a single drive can be more space efficient and may require less control equipment (not shown) in order to synchronize the clamping mechanisms  105 . The drive may include hydraulic cylinders, servo-drives, or other suitable systems. It is anticipated that the clamping system  100  herein will be space efficient while still providing adequate clamping forces for loads up to or in excess of approximately fifty tons per mold, although this is only an estimate. It will be understood that the actual load constraints will generally be determined by the physical strength of the materials, load capability of the bearings and the torque required to preload the elements into a state of mechanical lock. 
     In the embodiments herein, the clamping mechanism  105  requires relatively few mechanical parts, and will typically require less or no external lubrication, since all elements are intended to move on sealed bearings or bushings. The clamping system  100  is also intended to be space efficient and effective for molds that are horizontally wide or situations involving a plurality of side-by-side molds mounted to a single set of platens. As shown in  FIG. 1 , additional shaft supports (such as the spacer  115  and spacer bearing  120 ) may be added throughout the mid-span to counteract any drive shaft  110  whip. The clamping mechanisms  105  are intended to experience reduced wear over time due to the use of sealed bearings and bushings, thus reducing any variance in movements due to wear. The bearing components (spacer bearings  115 , shaft bearing  130 , pillow bearing  150 ) may be standard commercially available needle roller bearings or similar and the clamping system  100  can be configured such that the bearing components are easily replaceable to reduce overall maintenance costs. 
     The clamping system  100  may allow for the velocity of the clamping mechanisms  105  (and related press platen and mold) to rapidly decrease from the start of cycle to full clamp, giving a quick but gentle action to the mold. Likewise on the opening stroke, the movement of the clamping system  100  may accelerate more as the stroke is increased until a full-open position is reached. 
     As the clamping system  100  uses an eccentric hub  140 , the generated loads may typically be lighter until the angle of the connecting member approaches a few degrees off a straight line as shown in  FIG. 3A . The increase in load can therefore be inversely proportional to the velocity of action described above. This feature may be advantageous for overcoming large quick-intensity internal mold loads due to sudden injection or compression of material being molded into mold cavities and help to avoid the mold faces (i.e. first and second portions of the mold) “cracking” open momentarily during injection and packing pressures. This feature is intended to reduce the flashing on molded parts that can occur when the mold portions part during injection pressure. 
     As noted above, in some embodiments, a load cell or cells  155  may be attached to each clamping mechanism  105  in order to provide feedback of real-time clamping loads per angle of the eccentric hub  140  to a processor  160 , as illustrated in  FIG. 4 . This feedback may be used to provide mold-safety/protection in the event of a physical interference between the faces of the mold, or any other inhibitor to resistance-free closing. The mold press controls  165  may interact with the processor  160  to use the feedback from the load cell  155 . The feedback may be used to prevent press and mold damage, and for real time monitoring of loads during the molding cycle and amending the output  170 . For applications where more than one clamping mechanism  105  is used, for example, for wide spacing, the load cells  155  may also be used for comparative force data collection and real-time monitoring. For example, if a cavity opposite one eccentric hub or clamping mechanism was not pressurized the same as an opposing cavity opposite another clamping mechanism, this data can be reported and acted on in real time. 
     In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details may not be required in order to practice the embodiments. In other instances, well-known structures may be shown in simplified or block diagram form in order not to obscure the embodiments. 
     The above-described embodiments are intended to be examples only. Those of skill in the art can effect alterations, modifications and variations to the particular embodiments without departing from the scope, which is defined solely by the claims appended hereto. 
     Embodiments of the disclosure can be represented as a computer program product stored in a machine-readable medium (also referred to as a computer-readable medium, a processor-readable medium, or a computer usable medium having a computer-readable program code embodied therein). The machine-readable medium can be any suitable tangible, non-transitory medium, including magnetic, optical, or electrical storage medium including a diskette, compact disk read only memory (CD-ROM), memory device (volatile or non-volatile), or similar storage mechanism. The machine-readable medium can contain various sets of instructions, code sequences, configuration information, or other data, which, when executed, cause a processor to perform steps in a method according to an embodiment of the disclosure. Those of ordinary skill in the art will appreciate that other instructions and operations necessary to implement the described implementations can also be stored on the machine-readable medium. The instructions stored on the machine-readable medium can be executed by a processor or other suitable processing device, and can interface with circuitry to perform the described tasks.