Welding trajectory The welding trajectory of most compressors is an ellipse composed of four arcs. The centers of the arcs NP and MQ are OC and OE, respectively, and the radius is R2, ie: OCP=OCN=OEQ=OEM=R2 arc PQ The center of MN is OD, OF, and the radius is R1, that is: ODP=ODQ=QFN=R1. In the figure, a and b are the long and short half axes of the elliptical welding, respectively, and P, Q, M, and N are The tangent point of a circle of different radii (R1, R2).
Welding requires that the welding process is one of the key factors affecting the quality of the weld. In order to make the cross-sectional area of ​​each solder joint uniform during the whole-week welding process, so that the weld thickness is uniform, the appearance and the welding track accuracy are good, it is necessary to ensure that the linear velocity of the welding gun relative to the solder joint is constant at the solder joint. Ensure that the welding torch is always on the welding path of the workpiece, and that the distance from the welding torch to the workpiece solder joint is also kept constant (this distance is manually adjusted, not described in this article). Improving the performance of the two control systems is to improve the welding precision control. And position control to keep the welding torch always on the welding track of the workpiece.
The system's automatic shell sealer is a typical mechatronic device, so the system consists of a mechanical drive system and an automatic control system. The mechanical transmission system consists of a variable speed rotating mechanism and a straight-line position control mechanism. The workpiece to be welded is rotated one revolution on the rotary table, and the workpiece is welded.
As described above, the welding trajectory is elliptical, so the distance of the welding torch from the axis of rotation (i.e., the center of the ellipse) during the welding process is a Ï variable. To keep the wire speed of the torch relative to the weld, the rotational speed of the rotary table is also a variable. According to the analysis, the distance of the welding torch from the rotation axis line is related to the rotation angle of the rotary table, and the rotation speed of the rotary table is also related to the rotation angle. Through the measurement of the "rotation angle of the rotary table", the position system of the rotary rotary table system and the welding torch is organically constructed as an automatic profiling system.
Automatic Welder Control System Block Diagram The computer profiling system discussed in this paper. The hardware configuration is: select the appropriate PLC, frequency converter, AC motor, pulse encoder, stepper motor, etc., to form the frequency control system of the position control system and the weldment turntable. The law of motion of these two systems depends on the contour trajectory.
From the study of the mathematical model of speed and position control, it can be seen that the key components of the automatic control system are the angle/position converter and the angle/linear velocity converter, both of which are related to the rotation angle of the rotary table. The mathematical models of the controllers are: the linear velocity of the rotating system motor: Vr=Vr(")(1) The position of the welding gun position control system: Ï=Ï(")(2) The independent variables of the two mathematical models are Rotating the corner of the table, coordinate the rotation speed control system and the position control system through the corner to complete the contouring task of the welding trajectory.
Establishing the Mathematical Model The profiling system studied in this paper consists of the rotating system of the workpiece and the position system of the welding torch. The movement of the welding torch relative to the workpiece can be mathematically modeled as follows. The trajectory analysis chart takes the welding torch A as the research object, which is the moving point. The workpiece on the rotary table is taken as the motion reference system, that is, the moving system. Then the movement of the welding gun relative to the workpiece can be attributed to a composite motion problem at one point. If the movement trajectory of the welding torch relative to the workpiece is elliptical, the position of the welding torch can be expressed by the radial Ï of the ellipse. The movement rate of the welding torch relative to the workpiece is Vr, and Vr should satisfy the composite motion relationship: VA2=Vr2+Ve2 where: VA=Ï , Ve = Ï Ã— φ can obtain the linear velocity of the welding torch in the rotating system: Vr = Vr (φ) (3) Position control system position of the welding torch: Ï = Ï (φ) (4) As long as the formula (1), 2) The specific expression can be used to build a mathematical model.
Since the welding trajectory is a symmetrical figure, only a quarter of the segment can be studied, and each quarter segment is composed of two arcs. However, in order to simplify the control procedure, we study the half of the ellipse ( As MP section), as shown.
Conclusion The profiling control system discussed in this paper uses mathematical model control to complete the profiling of the contour trajectory and gives the welding mathematical model of the refrigerator compressor. According to the author's investigation, there are more than 20 kinds of elliptical compressors produced in domestic civil refrigerator compressors. If this mathematical model is adopted, only the ellipse parameters can be input.
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