The present invention relates to devices for lifting and separating flexible flat workpieces in a stack utilizing suction holders to grip the uppermost workpiece and to separate adjacent workpieces which are stuck together.
In current methods of machining flat sheet metal workpieces, the workpieces being processed are fed to the machine individually from a corresponding stack. Especially in cases where the stacked workpieces are coated with a film, and/or, in the case of metal workpieces, are oiled for corrosion protection, problems can occur when separating the workpieces because adjacent workpieces in the stack may stick together. This problem is encountered especially with thin workpieces.
To isolate flat, horizontally stacked workpieces, European Patent 0 639 519 discloses a device of the type mentioned previously, which uses a large number of suction holders next to another in the longitudinal direction on the edge of the workpiece. Some of the suction holders are reoriented along the edge of the workpiece in an effort to bend the edge upwardly and separate it from the sheet therebelow.
However, this device is not always effective in providing a reliably, functionally safe separating action.
It is the object of the present invention to provide a novel lifter and separator for stacked flexible flat workpieces which utilize a simple mechanical element to provide a highly effective and safe separator.
It is also an object to provide such a lifter and separator which is especially useful with thin flexible workpieces.
Another object is to provide such a separator which is relatively simple in construction and operation.
It has now been found that the foregoing and related objects and advantages may be readily attained in a sheet lifter and separator for lifting and separating the uppermost sheet of a stack of workpieces from the sheet disposed therebelow. This includes a lifter having a frame and a multiplicity of suction holders spaced thereabout with working surfaces at the lower ends to engage the sheet. At least one of the suction holders is disposed adjacent one side of the frame and thereby of the uppermost workpiece. A conduit is coupled to the holders and adapted to be coupled to a vacuum source to draw air from the holders and thereby secure the sheet thereto. The holder adjacent the one side is operable to bend the edge portion of the sheet adjacent the one side upwardly from the plane defined by the working surfaces of others of the holders which are spaced further inwardly from the one side.
Preferably, at least one holder adjacent the one side includes at least a first holder spaced at a first close distance to the one side and a second holder spaced at a second greater distance inwardly from the one side. Each of the holders has a suction holder sleeve provided on a suction holder base with the suction holder sleeve of the first holder being compressible to a greater extent than that of the second holder. When vacuum is applied to the workpiece surface, this provides a differential in vertical height to the working surface. The sleeves are of a bellows type configuration provided by multiple folds with the first holder having a greater number of folds than the sleeve of the second holder.
At least one workpiece stop is spaced from the one side along the imaginary line to limit upward movement of the workpiece during the bending process and it and the second holders are disposed along an imaginary connecting line running parallel to the side edge of the workpiece. Preferably, the one holder(s) adjacent the side is uncoupled from other holders placed on the outermost workpiece in the stack.
Preferably, at least one suction holder is disposed on a support structure that can move relative the lifter frame. This support structure is desirably a separator frame pivotally supported on the lifter frame, and at least one suction holder is pivoted thereby from a position in which it is aligned with the suction holders on the lifter frame to a position upwardly therefrom. The separator frame pivots relative to the lifter frame about an axis that is parallel to the one side of the lifter frame.
Also included is at least one separator nozzle mounted on the lifter frame adjacent the one side, and a conduit is connected thereto and adapted to be coupled to a source of pressurized air, whereby pressurized air can be released in the direction of the edge of the workpiece to facilitate separation of the uppermost sheet. This air supply can include means for releasing the pressurized air in pulses, and desirably there are a multiplicity of separator nozzles staggered in relationship along the one side of the frame.