Electric heating – Metal heating – By arc
Reexamination Certificate
1998-12-02
2001-09-25
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C083S940000, C083S076100
Reexamination Certificate
active
06294755
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to apparatus and method for controlling Cartesian positioning of a laser nozzle for cutting patterns out of flat stock. In particular, apparatus comprises X-Y positioner in an H configuration which uses linear motors to drive the gantry, and includes optimization methods such as joining and filleting sequential connected move vectors. Accommodation is made for real world constraints including time and distance being measured in discrete integer increments.
BACKGROUND OF THE INVENTION
A known method of laser cutting patterns in material is to advance a finite length of material into a cutting zone, and while the material is stationary, using a laser beam nozzle mounted to a X-Y positioner for emitting a laser beam to cut the pattern from the material.
The numerically controlled positioner positions the laser beam over the material in response to a predetermined known pattern. Once the pattern is cut the conveyor advances to eject the cut pattern and bring new material into the cutting zone.
Increases in throughput have been achieved by implementing multi-ply cutting, increasing the speed at which the laser moves and using rapid conveyor movement to eject material.
In Canadian Patent Application published in Canada as application number 2,016,554 in Nov. 11, 1991, a method is disclosed which partially achieves the objective of increasing the throughput of cut patterns by enabling laser cutting while material is moving in a continuous manner through the positioner laser cutting zone. This “Cut-on-the-Fly method provides two-fold savings: it eliminates the loading and unloading of material from the cutting zone; and it takes advantage of movement of the cutting head along the axis of the conveyor as well as across the conveyor. The conveyor and the fabric is passed through a rectangular (X&Y axes) cutting zone of finite dimensions. A laser nozzle is suspended from an X-Y positioner. The heavier laser itself is located remote from the positioner. The positioner is movable in X and Y axes for manipulating the laser nozzle and emitted laser beam within the cutting zone. A computer directs the positioning of the laser nozzle, its velocity and its acceleration. The laser nozzle is required to stop at each non-tangent intersection of discrete moves. The nozzle cannot accelerate through a curve.
The fabric is cut according to patterns specified in a data file. The conveyor moves through the cutting zone continuously, The laser beam must cut the pattern before the fabric leaves the cutting zone. The speed at which cut fabric may be produced is dependent upon factors including laser power, the physical speed at which laser nozzle can be manipulated through the cutting zone and optimization of the sequence of the cuts made so as to minimize wasted (non-cutting) movement and to ensure continuous movement of the conveyor. Accuracy of the cut, and hence the accuracy of the geometry of the pattern, is dependent upon the physical resolution of the positioner and the nature of the instructions given to the positioner.
The positioner used with the Cut-on-the-Fly apparatus described above employs a gantry which manipulates and positions the laser nozzle. Stepper motors are used to incrementally move the gantry along the X-axis and a stepper motor drives the laser nozzle along the Y axis. One stepper motor is used for X-axis control and is located on one end of the gantry.
Several issues arise when using stepper motors in moving a laser nozzle. First, the stepper motors do not provide the high resolution need for precise control, particularly at high speeds. Stepper motors are relative positioning devices, i.e. increment three steps from this position. As a result, the controller will still be feeding absolute coordinates to the positioner, but the stepper could have inherited an offset and are subject to slipping at high speed. The steppers become less effective as the demand for greater speed increases. The force produced by stepper motors is maximal at rest and falls off as the stepper speed increases. With the demand for greater and greater speeds, a stepper motor is pressed into service at its worse operating range, where little force is available to effect rapid changes in velocity. Further, if the laser nozzle is at the opposing end of the gantry from the stepper motor, then mechanical lag can result when driving the laser nozzle along the X-axis.
Accordingly, it is known in the prior art to provide:
An X-Y axes positioner upon which the lens and mirrors of a laser are suspended for issuing a laser beam to cut underlying material;
incremental or continuous conveyor movement for passing material beneath a laser cutting means;
user of stepper motors to control gantry movement;
use of a geometry set from which the pattern is determined, cut lines are calculated and optimization of the cutting sequence is performed; and
use of a computer program to direct the laser position and coordinate laser position and continuous conveyor movement.
Challenges associated with cutting continuously moving materials include: p
1
a. directing the positioner to cut along all of the cut lines on the material before the material moves out of the cut zone;
b. avoiding starting and stopping the laser nozzle movement, associated with lost time to decelerate and accelerate the nozzle;
c. avoiding high velocity during repositioning of the laser nozzle which can exceed the limited power laser's ability to cut the material, resulting in missed threads or uncut zones.
In is known to perform certain optimization by:
a. minimizing the time for “dry haul”, that is, where the laser beam is not actively cutting but is merely being re-positioned;
b. planning to cut lines to cut the perimeter of the space between the patterns as opposed to the greater traversed distances for cutting the perimeter of the pattern itself; and
c. predetermining the optimal cutting sequence.
In order to increase the throughput of the system the positioner movement can be further optimized by both minimizing stop and go, enabling acceleration through a curve, avoiding exceeding maximum velocities and accelerations, and by modification of the positioner to enable high acceleration while maintaining accurate positioning.
SUMMARY OF THE INVENTION
Minimizing positioner stop and go, minimizing time to move the tool through a path, and maximizing acceleration requires improved control of the positioner and improved positioner apparatus.
Improved positioner apparatus is achieved by providing:
improved positioner structure; and
improved positioner feedback.
Improved control of the positioner is provided by:
modifying the tool path to minimize stop and go;
modifying the tool velocity profile throughout the path to minimize time while adhering to limitations including maximum tool acceleration, velocity and being cognizant of integer values for position and time; and
controlling conveyor movement to ensure continuous movement and continuous velocity across bites.
The improved system integrates improved optimization of positioner control, elimination of conveyor stoppage and an improved positioner apparatus which provides increased resolution, accuracy, and acceleration. All of the above contribute and result in increased material throughput which can be in the order of 15 to 20% faster than prior art apparatus and processes.
While the invention was developed in the context of cutting fabric with a laser, any tool which must be moved quickly along a continuous path will be beneficially affected by the improved throughput of apparatus fitted with the improvements.
Simply put, positioner apparatus is improved to provide increased acceleration response and increased precision for complementing optimization routines disclosed herein. Improved response is achieved in part by providing a gantry with independent drives and pivotal ends. Linear servo motors independently drive each of the two ends of the gantry and the tool (laser nozzle) along the gantry. The gantry structure is optimized to be lightweight, yet continue
Andrews Randall G.
Sawatzky Brian D
Want Chris
Heinrich Samuel M.
Lacent Technologies Inc.
Millen White Zelano & Branigan P.C.
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