STITCHING SYSTEM WITH REAL-TIME STEERING CONTROL
A stitching system is configured to stitch through decorative skins with a molded seam recess representing a seam and includes a sewing machine, an image acquisition mechanism, a controller, and a rotation mechanism. The sewing machine is rotatable with respect to a support table, and includes a sewing head to receive a sewing needle and a sewing foot to selectively engage the skin. The image acquisition mechanism produces an image of the seam recess with respect to the sewing head/needle(s). The controller determines the difference between the actual recess location and a predetermined desired recess location. Based on this difference, the controller determines a sewing machine rotation angle and orientation to reduce the difference to zero, and then produces a corresponding adjustment signal that drives the rotation mechanism. A robot can move either the sewing machine or the workpiece, and still use the herein-described real time steering control.
1 . A stitching system configured to stitch through an automotive interior skin with a molded seam recess between generally exposed top and bottom surfaces thereof, comprising:
a sewing machine disposed proximate a stationary support table and including a sewing head with a sewing foot and a sewing needle receiver for receiving a needle, said sewing machine being rotatably coupled to a pivoting base wherein rotation of said sewing machine rotates at least said sewing head and said sewing foot about a swivel axis that is generally parallel to a needle axis through said sewing needle, said swivel axis being offset from said needle axis;
a sensor in proximity to said sewing head and configured to produce an output indicative of an actual location of the recess in the skin;
an electronic controller, including an electronic processor, configured to determine a difference between said actual location of the recess and a predetermined, desired location of the recess based on said sensor output, said controller being further configured to determine a rotation angle and orientation for said sewing machine that is configured to reduce a magnitude of said difference, said controller being further configured to produce an adjustment signal indicative of said determined rotation angle and orientation; and
a rotation mechanism responsive to said adjustment signal configured to rotate said sewing machine in said determined rotation orientation to said determined rotation angle.
2 . The system of claim 1 wherein the sewing needle is a first sewing needle and said needle axis is a first needle axis, said sewing machine head further including a second sewing needle having a second needle axis associated therewith, said swivel axis being generally parallel to said first and second needle axes, said swivel axis being offset from said first and second needle axes by a predetermined distance.
3 . The system of claim 1 further comprising a display proximate said sewing machine and electrically coupled to said controller, said display being configured to emit a first light signal when said difference is less than a first threshold.
4 . The system of claim 3 wherein said display is configured to emit a second light signal when said difference exceeds said first threshold and is less than a second threshold that is greater than said first threshold.
5 . The system of claim 1 further comprising a display proximate said sewing machine and electrically coupled to said controller, said display being configured to emit a queuing light signal when an a curvature radius of the mold seam recess is expected to change beyond a predetermined threshold.
6 . The system of claim 1 wherein said sensor comprises an image acquisition mechanism configured to acquire an image in a predetermined region proximate said sewing head.
7 . The system of claim 1 wherein said rotation orientation is one of a clockwise (CW) direction and a counter-clockwise (CCW) direction.
8 . The system of claim 1 wherein said controller comprises:
control logic stored in memory and configured for execution by said processor, said control logic being configured to determine said rotation angle and said rotation orientation in accordance with a proportional-integral-differential (PID) control strategy, said PID control strategy being responsive to at least said determined difference.
9 . The system of claim 8 wherein said sensor comprises an image acquisition mechanism configured to acquire an image of a predetermined region proximate said sewing head, said controller further comprising:
image processing logic stored in memory configured for execution by said processor configured to analyze said image so as to (i) identify a first location of the recess in a pixel space of said image; (ii) identify a second location in said pixel space; and (iii) determine said difference by assessing said determined first and second locations.
10 . The system of claim 9 wherein said image processing logic is further configured to translate said difference in pixel space to a corresponding difference in an at least one dimensional physical space.
11 . The system of claim 8 wherein the recess of the skin includes at least one segment, said PID control strategy has associated therewith at least a first set of coefficients respectively associated with proportional, integral and differential terms of said PID control strategy, said first set of coefficients being used by said PID control strategy to determine said rotation angle and said rotation orientation over said first segment.
12 . The system of claim 11 wherein the recess further includes a second segment different than said first segment, said PID control strategy having associated therewith a second set of coefficients associated with proportional, integral and differential terms of said PID control strategy different from said first set of coefficients, said second set of coefficients being used by said PID control strategy to determine said rotation angle and said rotation orientation over said second segment.
13 . The system of claim 8 further including a proximity detector configured to sense a stitch by said sewing needle and generate a stitch counter signal in response thereto, said control logic being further configured to
maintain the current stitch count along a feed path defined by the recess of the skin; and
determine said rotation angle and said rotation orientation as a function of said current stitch count.
14 . The system of claim 13 wherein said control logic further includes a compensation data structure including stitch number-versus-compensation value data.
15 . The system of claim 1 wherein said control logic further includes:
de-activation logic stored in memory and configured for execution by said processor, said de-activation logic being configured to disable generation of said adjustment signal when a sewing speed falls below a predetermined threshold.
16 . The system of claim 15 further including a proximity detector configured to sense a stitch by said sewing needle and generate a stitch counter signal in response thereto, wherein said sewing speed is based on at least time intervals between successive assertions of said stitch counter signal.
17 . The system of claim 1 wherein said rotation mechanism includes a servo drive responsive to said adjustment signal configured to actuate a ball screw coupled to a lever arm, said lever arm being further coupled to said pivoting base for rotation of said sewing machine.
18 . The system of claim 1 further comprising an illumination source disposed with respect to said sewing machine so as to project oblique illumination on the automotive interior skin to cast a shadow on the seam.