Modular microprocessor-controlled controller for resistance for resistance welding machines

#Resistance welding processes are widely used in the manufacture of sheet metal assemblies, such as automobile and aircraft bodies. Each resistance weld involves a sequence of electrical energy and mechanical pressure steps. The sequence is provided by a controller which governs the timing of both the electrical and the mechanical steps. For example, the controller may establish a selected number of cycles of A.C. line power at a selected current, with a selected electrode force for each step of a welding operation. In carrying out the welding operation, the operator merely presses a button which sets the controller in operation. The controller then responds to an internal program to carry out all the steps necessary for the operation. The program of the controller is stored in an internal memory, and it may vary from a relatively few commands to a large number of commands, depending upon the simplicity or complexity of the welding operation.

#The controller of the invention is controlled by a microprocessor, as mentioned above, which has programmable read-only and random access memories associated therewith. The controller provides heat and pressure commands to the controlled resistance welding machine. The controller includes a digital circuit for compensating for line voltage variations and disturbances, as mentioned above. This circuit digitizes the RMS input voltage and computes the proper firing time to maintain constant power during line voltage fluctuations and disturbances. The firing times are controlled by silicon controlled rectifiers or ignitrons, as will be described. Over-temperature protection of the devices may be provided in the manner described and claimed in U.S. Pat. No. 4,039,928, which is assigned to the present assignee.

#A relatively inexpensive controller for a resistance type welding machine is provided which is modular in nature, and which is microprocessor controlled. The controller includes a master control module which incorporates line voltage compensation, and which is standard for all models, and it also includes a personality module which is programmed to fit the individual customer needs, as well as the needs of various welding operations in the individual customer's plant.

#FIG. 1 is a perspective representation showing a typical resistance welding machine controlled by a modular controller constructed in accordance with the concepts of the invention;

#FIG. 2A is a front elevation, and FIG. 2B is a perspective, representation of one embodiment of the controller of the present invention, illustrating the front control panel of the controller;

#FIG. 3 is a block diagram of the various logic components which are included in the master control module of the controller;

#As shown in FIG. 1, a typical resistance type welding machine is designated 10. The welding machine 10 includes electrodes 12 and 14 which, when the machine is operated, are squeezed against the opposite sides of the workpiece, and an electric current is then passed through the electrodes and through the workpiece to accomplish the desired weld.

#The movement of the electrodes 12 and 14, and the current flow through the electrodes, are controlled by a controller 16 which is constructed in accordance with the concepts of the present invention. The controller 16, as shown in FIGS. 2A and 2B includes a master control module 18 and a personality module 20.

#The personality module 20 includes a series of pairs of thumbwheel switches which are designated #1-#9, in the particular embodiment under consideration, although more or less such switch pairs may be used, depending upon the particular application to which the controller is to be placed. The switch pairs #1-#6 in the illustrated embodiment are used respectively to control the number of cycles of current during the interval in which the electrodes are being squeezed against the opposite sides of the workpiece, to control the number of current cycles prior to the commencement of the actual welding operation, to control the number of current cycles as the actual weld is being formed, to control the number of current cycles after the actual weld has been formed, to control the number of current cycles during a hold operation, and to control the number of current cycles for which an off condition is to occur between successive welding operation. The switch pairs #7, #8, and #9 control the amount of power to be delivered before, during and after the end of the weld during any particular welding operation. Power is linearly increased during a pre-slope interval; it is held constant during the weld interval before the weld is initiated; and it is linearly decreased during a post-slope interval after the weld has been completed.