1.  Field of the Invention
This invention relates to stops used in controlling the feeding of material as a workpiece to a machining operation, such as cutting a length of the material on a band saw, and more particularly, to an adjustable stop which compensates for undesired movement of the workpiece.  The stop is illustrated in conjunction with a shuttle vise on a band saw, but the stop may be used in other applications, such as the feeding of material to a punch press, etc. 
2.  Description of the Prior Art
Machines for cutting material, such as large band saws which are used to cut workpieces formed of elongated materials, are well known in the art.  The workpiece material is positioned on a feed conveyor adjacent to the saw blade and moved into a cutting position under the saw blade by a shuttle vise which is moved to a clamping position to initially clamp the material and then move in a direction toward the saw blade and to a cutting position.  A stop is sometimes used to limit movement of the shuttle vise and to insure it stops at the desired cutting position.  As the material is moved, it extends beyond the saw blade onto a receiving conveyor where it is clamped by a fixed vise adjacent to the saw blade.  At this point, the material is cut by the saw blade.  While the saw blade is cutting, the shuttle vise is released from the material and moved back to the desired clamping position to clamp the material again and move it to the cutting position for the next cutting operation.  This type of saw works well for many applications where the cut length of the material is not particularly critical. 
However, in cases where the cut length of the material may be critical this prior art saw may not be able to position the material in the cutting position accurately enough to insure that the cut length is within the desired tolerances.  Closer tolerance requirements are becoming more common.  The problem has to do with the straightness of the material, surface imperfections, and/or flexibility of the material and the deflection thereof when clamped by the shuttle vise.  When the vise clamps the material, the clamping action may actually cause the shuttle vise to move slightly due to these variations in the material.  This means that the shuttle vise is moved away from or toward the stop with the result that the cut length of the material may be correspondingly longer or shorter than desired.  Obviously, if the movement of the shuttle vise can be greater than the cut length tolerances on the workpiece, this is very undesirable. 
The present invention solves this problem by providing an adjustable stop to compensate for the amount of undesired movement of the shuttle vise and transmitting a signal to a controller which adjusts the position of the stop.  Thus, when the shuttle vise moves to the cutting position and engages the adjusted stop, the cut length of the material will be at the proper length.  That is, the adjustment of the stop compensates for the undesired movement of the shuttle vise so that the cut length of the material stays within the desired tolerances.  Also, the encoder will detect the incorrect position of the shuttle vise and will adjust the front stop to compensate for the positional error in the shuttle vise.  In addition to this positional adjustment, when the shuttle vise clamps the material to be cut, the encoder will detect variances which occur while clamping and will make an adjustment for that error also. 
It will be understood by those skilled in the art, that this adjustable stop apparatus is useful in any application in which material is clamped and moved.  Accordingly, the invention is not intended to be limited to a band saw application. 
The present invention may be described as a material cutting apparatus comprising a feed conveyor, a band saw adjacent to the feed conveyor, a shuttle vise movably disposed on the feed conveyor and an adjustable stop on the feed conveyor for adjusting a distance between the stop and the shuttle vise.  The shuttle vise is adapted for clamping a workpiece on the feed conveyor when in a clamping position and moving the workpiece to a cutting position adjacent to the band saw.  The stop is also adapted for stopping the shuttle vise at the cutting position.  Preferably, the stop is adapted for adjusting the distance between the stop and shuttle vise in an amount equal to movement of the shuttle vise caused by clamping the workpiece or errors in the initial positioning. 
The apparatus may further comprise an encoder adapted for generating a signal in response to the movement of the shuttle vise and an actuator for moving the adjustable stop in response to the signal.  The apparatus may further comprise a controller for receiving the signal and transmitting this signal to the actuator. 
The apparatus may additionally comprise a positional sensor for sensing a position of the adjustable stop and transmitting a positional signal in response thereto to the controller.  The positional sensor may a transducer, switch or other type of sensor. 
In one embodiment, the adjustable stop comprises a wedge having an angled face opposite the shuttle vise and an actuator for moving the wedge transversely with respect to the feed conveyor.  The actuator is characterized by any linear motion device, such as a pneumatic or hydraulic cylinder.  In this first embodiment, the apparatus may further comprise a bumper disposed on the shuttle vise.  The bumper has an angled face corresponding to the angled face on the wedge, and movement of the wedge results in varying the distance between the face on the bumper and the face on the wedge. 
In a second embodiment, the adjustable stop comprises a stepped member having a plurality of faces directed toward the shuttle vise and an actuator for moving the stepped member transversely with respect to the feed conveyor.  The actuator may be the same or similar to that described for the first embodiment.  In the second embodiment, the apparatus may further comprise a bumper attached to the vise and having a face thereon.  The actuator is adapted for moving the stepped member such that a selected one of the plurality of faces is aligned with the face on the bumper. 
In a third embodiment, the adjustable stop comprises a sleeve, a shaft threadingly connected to the sleeve, and a prime mover for rotating the shaft.  The shaft has an end with a face thereon directed toward the shuttle vise.  Rotation of the shaft varies the distance between the face and the shuttle vise.  The third embodiment may further comprise a bumper attached to the shuttle vise and adapted for engaging the face on the end of the shaft.  The prime mover may be directly connected to the shaft or may be connected to the shaft by a drive train such as a first pulley connected to the shaft, a second pulley connected to the prime mover, and a belt interconnecting the first and second pulleys.  It will be understood that the adjustable stop mechanism could be mounted on the shuttle vise and the fixed bumper attached to the saw frame. 
Preferably, in the third embodiment, the apparatus further comprises a spring engaging the shaft and biasing the shaft longitudinally with respect to the sleeve for eliminating play in the threaded connection between the shaft and sleeve.  The third embodiment may also comprise a switch and a cam rotatable by the prime mover and having a cam lobe thereon for engaging the switch when the cam is in a predetermined position.  This predetermined position preferably corresponds to a longitudinal mid-point of the shaft.  The switch is connected to the controller for the shuttle vise so the system can be reset with the location of the shaft known. 
In a fourth embodiment, the adjustable stop comprises an eccentric cam and a prime mover for rotating the cam.  Rotation of the cam varies the distance between the cam surface and the shuttle vise.  A bumper may be attached to the shuttle vise and adapted for engaging the cam surface.  The prime mover may be directly connected to the cam, such as by a shaft, or may be connected to the cam by a drive train, such as a belt-and-pulley assembly. 
The present invention may also be described as a method of cutting a workpiece comprising the step of (a) providing a material cutting apparatus comprising a feed conveyor, a band saw adjacent to the feed conveyor, a shuttle vise movably disposed on the feed conveyor, an adapter for clamping a workpiece on the feed conveyor when in a clamping position and moving the workpiece to a cutting position adjacent to the band saw, and a stop on the feed conveyor for stopping the shuttle vise at the cutting position.  The method further comprises the steps of (b) detecting movement of the shuttle vise resulting from clamping the workpiece and (c) adjusting the stop on the feed conveyor for compensating for the movement of the shuttle vise such that a distance between the shuttle vise and the stop remains substantially constant.  Step (c) may also comprise adjusting the stop for compensating for initial inaccurate positioning of the shuttle vise. 
Step (c) may comprise generating a signal in response to the movement of the shuttle device and transmitting the signal to an actuator for moving the adjustable stop in response to the signal. 
In one embodiment, step (c) comprises moving a wedge on the stop transversely with respect to the feed conveyor.  In another embodiment, step (c) comprises moving a stepped member having a plurality of faces thereon transversely with respect to the feed conveyor.  In still another embodiment, step (c) comprises rotating a shaft connected to the stop.  In an additional embodiment, step(c) comprises rotating an eccentric cam to vary the distance between a cam surface on the cam and the shuttle vise. 
Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiments is read in conjunction with the drawings which illustrate such embodiments.