Patent Application
20080134740
1. Field of the Invention
The present invention relates to a blank or part sensing system for sheet metal forming tools that permits sensing the presence of a blank or part during a forming process.
2. Background Art
Metal parts may be formed in sheet metal forming process in which a blank is formed in a series of steps into a finished part. Several presses may be arranged and aligned to sequently form a part. Parts may be initially drawn in a draw die, and then may be spanked, trimmed, and punched in subsequent press forming operations. The sheet metal parts may also be made in a transfer press in which a die having multiple stations is operated by a single press that has a die with multiple stations that perform prescribed steps in sequence to form a finished part.
Sensors are used in sheet metal forming processes to control the operation of one or more presses. Sensors may be provided in the dies and also may be provided on loaders, shuttles, conveyors and other material handling equipment that is used to load blanks or partially formed parts. Different types of sensors may be used in sheet metal forming processes include limit switches, reed switches, Hall Effect switches, or proximity sensors.
One application for a sensor used in a sheet metal forming tool is as a blank or part presence detector. A part presence detector is used to detect whether a sheet metal blank or a partially formed part is in the proper position for performing the next operation. If a part presence detector provides a false indication that a part is in the desired position the part, die, or tool may be damaged if, in fact, the part is out of location. If a part is mishit by a sheet metal forming tool the part may be scrapped and the tool may be damaged. If a part presence detector indicates the presence of a panel when no panel is in the tool, the tool may be damaged. If a sheet metal forming tool is cycled without performing the desired the operation on the part, the number of parts produced may be inaccurately reflected.
Variations in the strength or resiliency of a blank or part may result in unexpected spring back in the part after a forming operation. Bowed blanks or parts may be difficult to sense by a part presence detector since the blank may be bowed in an area where the sensor is oriented to detect the presence of the blank.
High speed production lines have short cycle times that afford less time for a blank or part to nest within the tool. Less time is also available for sensing that the part is properly nested in the tool. Some part shapes present challenges for locating sensors that accurately and quickly sense the location of a blank or part.
In some instances, it would be advantageous to provide a part presence detector that senses the presence of a part throughout a forming process even as the edge of a part moves during the drawing or forming cycle.
There is a need for an accurate system for sensing the presence of a blank or part. There is a further need for a part sensing system that provides a quick response and is capable of providing an accurate indication of the presence of a part throughout a forming cycle. By providing an improved part presence detecting system a reduction in false signals from the part sensing system can result in reduced downtime and scrap.
The above problems and needs are addressed by applicant's invention as summarized below.
A sensing system for a sheet forming tool is provided that senses the edge of a blank or part on a blank holder throughout a forming cycle. The sheet metal forming tool is loaded with a blank or other part and has an upper die that is moved reciprocally relative to a lower die in a drawing cycle. The sensing system comprises a blank holder assembly that has a support member on which the blank nests when loaded. A proximity sensor is attached to the blank holder assembly adjacent to the support member. A fluid cylinder having an extensible rod supports the blank holder and proximity sensor. The rod is moved by the cylinder between a raised position and a lowered position. The fluid cylinder biases the rod toward the raised position. The upper die operatively applies an opposing force to the bias of the cylinder to cause the blank holder and proximity sensor to be moved to the lowered position. The proximity sensor senses that an edge of the blank is located on the blank holder throughout the course of the press cycle.
Other aspects of the sensing system may comprise that the blank holder and proximity sensor are moved away from the die during the forming cycle by the upper die. The support member may have a blank supporting surface that supports the blank about its periphery. The blank holder has at least one blank loading guide that guides the blank into the blank holder.
In addition, the blank holder may have a fixed bracket that is fixed relative to the lower die and a movable bracket that supports the support member and the proximity sensor for movement in response to movement of the upper die. A controller controls the operation of the tool in response to the proximity sensor sensing the presence of the blank. The sensor generates a signal that is provided to the controller and is processed to permit operation of the tool.
In another embodiment, a sensor assembly is provided for a forming tool that is used to form a sheet metal part. The sensor assembly comprises a fluid cylinder having an extensible rod that is moved between the retracted position and an extended position. A part holder assembly has a fixed bracket that is fixed relative to a lower portion of the tool and a movable bracket that is attached to the extensible rod of the fluid cylinder and includes a part supporting member. The sensor is attached to the movable bracket of the part holder and is located adjacent to the part supporting member. The upper portion of the tool reciprocates relative to the lower portion of the tool. The cylinder urges the extensible rod to the extended position which raises the movable bracket including the part supporting member and sensor until the upper portion of the tool engages the movable bracket. The bracket and extensible rod are moved against the force of the cylinder toward the retracted position when the upper portion of the tool engages the movable bracket.
According to other aspects of the above sensor assembly, the movable bracket, sensor and rod return to their raised positions as the upper portion of the tool moves away from the lower portion of the tool during a forming cycle. The blank supporting member has a blank supporting surface that supports the blank about a portion of the periphery of the blank. The blank holder assembly has at least one blank loading guide that guides the blank to the blank supporting member. A controller controls the operation of the metal forming tool based in part upon the output of the sensor that senses the presence of the part. The sensor generates a signal that is provided to the controller and processed in the course of continued operation of the forming tool.
A method is also provided for sensing the position of a sheet metal part during a forming cycle of a press. The press has an upper portion that moves reciprocally relative to a lower portion of the press. A tool is attached to the press that has a part holder assembly including a fixed bracket that is fixed relative to the lower portion of the press and a movable bracket that is attached to an extensible rod of a fluid cylinder. A part supporting member and a sensor that is disposed adjacent to the part supporting member is attached to the movable bracket. The method starts with loading a part into the part holder assembly. The presence of the part in the part holder assembly is initially sensed by the sensor. The upper portion of the press is lowered to form a part and also drives the movable bracket against a biasing force applied by the fluid cylinder. The position of the part is continuously sensed by the sensor during the forming cycle of the press. The movable bracket of the part holder assembly that is attached to the extensible rod of the fluid cylinder is returned to a part loading position as the upper portion of the press is raised.
According to other aspects of the method, during the step of raising the upper portion of the press, the movable bracket of the part holder assembly may be placed in contact with and follow the upper portion of the press until an upper limit of movement of the movable bracket is reached. The upper portion of the press continues to move after the upper limit of movement of the movable bracket is reached to provide clearance for loading and unloading parts. The sensor may generate a signal indicative of the presence of a part that is sent to a controller. The controller only permits operation of the press if the signal is received by the controller during designated periods of the forming cycle. A second tool may be provided with a second part holder assembly to which the part is transferred for subsequent forming operations. The steps of the method may be repeated with the second tool. The sensor may sense the edge of the part as the edge of the part moves toward the forming cavity.
These and other aspects and optional features will be better understood in view of the attached drawings and the following detailed description of the illustrated embodiments.
Referring to
The sensing system 10 includes a blank holder assembly that is generally indicated by reference numeral 24. The blank holder assembly 24 is connected to a fluid cylinder 26.
Referring to
Referring to
Referring to
After the blank 30 has nested in the blank holder assembly 24, as shown in phantom in
The movable bracket 36 including the proximity sensor 46 and support member 40 move reciprocally as shown by the double headed phantom arrows in
The proximity sensors 46 should be calibrated to sense the edge 52 of the blank 30 and formed part 30′ throughout the forming cycle even if the edge of the blank 30 moves away from the proximity sensor 46. The die pins 18 drive the movable bracket 36 downwardly against the force applied by the fluid cylinders 26 on the downstroke of the press. The fluid cylinders 26 urge the movable bracket 36 upwardly on the up stroke as limited by the upward movement of the die pins 18.
While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
