Medar, Inc.

Welding Technology Corporation

John Foster Farrow

Jeffrey J Mason

David W Schulz

The invention is a simple amplifier circuit for a current transformer to measure very small AC currents, as required for ground fault detection. The circuit presents a very low impedance to the current transformer output and provides high amplification of the current transformer signal. Concurrently and with no additional components, the inventive circuit supplies a bias current to the current transformer to improve its performance and provides output signals which can be used to detect disconnection of the current transformer or a short circuit between either of the current transformer terminals and ground.

Amplifier circuit for a current transformer

The invention comprises a set of methods to detect the resistance of a connection to safety ground and to detect the presence of voltage hazardous to people in systems where an unknown amount of current intermittently flows in the safety ground circuit. Samples of voltage between two points in the safety ground circuit are taken repeatedly. When the voltage caused by the unknown currents in the safety ground circuit is below a preset threshold, a known current is applied and another voltage sample is taken to detect the electrical resistance of the safety ground circuit. If an excessive resistance or voltage is detected, one or more outputs are activated or deactivated to indicate the problem and remove power from the system. The invention requires no current sensor for its operation.

Methods to detect hazardous conditions in a safety ground circuit in the presence of ground loop currents and electrical noise

A rotary circuit breaker door safety interlock for use with a power switch actuated by a rotating shaft installed in a enclosure with a hinged door is disclosed. The door safety rotary circuit breaker interlock functions both to prevent the enclosure door from being opened unless the power switch has first been turned OFF, and to prevent the power switch from being turned ON while the enclosure door is open. The door safety rotary circuit breaker interlock can be intentionally overridden to allow the enclosure door to be opened without turning the power switch OFF, and to allow the power switch to be turned ON while the enclosure door is open. The door safety rotary circuit breaker interlock is simple mechanically, requires no springs or deformable members for its operation, and can be adapted to many mounting variations in enclosures having doors that hinge at the left, right, top, or bottom.

Door interlock for rotary actuated circuit breaker

This invention relates to methods to control the resistance spotwelding process using an electric servomotor actuator to move the welding electrodes to the work and apply force to them. Measurements of actuator position, servomotor drive voltage, servomotor drive current, voltage across the welding electrodes, welding transformer primary current, welding transformer secondary current and power factor in the primary circuit of the welding transformer are used separately and in combination to determine various conditions such as identify defects in the welding machine, the electric cabling, the welding process and in the weld itself. Depending upon the defect found, the welding parameters are changed to overcome the defect, and/or the need for an additional weld is indicated and/or an error indication is generated.

Method for determining a condition of a resistance spotwelding system or a workpiece in the system

A signal integrator stabilization circuit comprises an operational amplifier functioning as a comparator. The circuit further comprises an attenuator in the amplifier's feedback, thereby generating a feedback signal which is sampled to produce a sampling signal. The integrator is driven with a preselected ratio of the feedback signal and the sampling signal to produce a stabilized output signal approaching a zero value which has a good DC stability without compromising the ability to accurately integrate high frequency signals.

Method of stabilizing an electronic signal integrator

A method and system for controlling the output current of large, low-voltage, DC power supply which includes at least one transformer primary by controllably switching an AC power line voltage to the primary as a function of actual and desired output currents. SCRs are used to switch, using phase control, the AC primary voltage to the transformer(s) of the power supply in order to control the output current. Given the incoming power line voltage, the current value from the previous power line cycle and the desired current for the present cycle, the function is used to find the SCR firing angle to attain the desired output current in the present power line cycle. Actual measurements of output current and power line voltage are used to modify the function to reflect changes in power line voltage and/or circuit impedance to obtain a modified function. Preferably, instantaneous changes in power line voltage are measured and used to change the input variables to the function in order to provide instantaneous corrections for power line voltage changes. Diagnostic information concerning the operation of the DC power supply is determined from the modified function.

Method and system for controlling output current of a large,

A method is disclosed for controlling the magnitude of current delivered through welding electrodes to a workpiece to be welded using resistance welding techniques, in order to prevent weld expulsion and concomitant diminishment of weld quality. Weld expulsion is detected by determining changes in resistance during formation of the weld, by periodically determining the power factor, and the primary circuit of the welding transformer. The power factor is determined by determining the relative timing between the commencement of the applied voltage, the zero crossover point of the applied voltage, and the ensuing zero point of the applied current.

Automatic stepper for resistance welding

Structure for and method of controlling the firing point of thyristors in a phase controlled contactor in a resistance welding circuit in accordance with variations in current line voltage and/or one of resistance and inductive impedance in the welding circuit including structure for and the method of determining the firing point in a cycle of alternating electrical energy fed to the welder in terms of its distance from zero voltage cross over point and determining the current lag after a subsequent zero voltage cross over point of the voltage signal, determining the power factor of the welding circuit from these angular measurements and selecting a new firing delay for the contactor in accordance with the circuit power factor and the percent heat selected in the welding circuit, and subsequently correcting the firing delay in accordance with the percent heat selected in view of changes in the line voltage and circuit current.

Method and apparatus for determining the power factor of a circuit

High frequency resistance spot welding structure and method. In one embodiment, the structure includes dual, mirror image welding transformers, each including a transformer secondary circuit, an endless transformer core, and a transformer primary winding wound around the transformer core. The transformer secondary circuits may be single member, U-shaped transformer secondaries with integral electrode portions. In another embodiment, one of the transformers is replaced by a pair of spaced apart welding electrodes which are connected by a conductor. Means are provided for supplying welding pressure to the transformers to move them with their associated welding electrodes during a weld sequence. A high frequency, electrical welding signal is applied to the transformer primary circuits which are synchronized when two transformers are used so that the welding currents passing through the transformer secondary circuits reinforce each other. The structure is small and light weight so as to be inexpensive, positioned immediately adjacent a weld, and moved quickly. The method of the invention includes providing the high frequency welding signal to the mirror image, closely spaced apart welding structures, synchronizing the high frequency welding signal to provide push/pull welding and providing forging pressure through the transformers or transformer to move them with their associated electrodes during spot welding.

High frequency resistance spot welding structure and method

Structure for and a method of resistance welding using an induction coupled power source. The structure of the invention comprises an electric coil wrapped around a flux concentrating core in close proximity to members to be welded together, a source of alternating electrical energy connected through the coil and means for applying pressure between the members to be welded. In accordance with the method of the invention the members to be welded are heated by at least one of an induced current and hysteresis loss and the heated members are then forged together by applying pressure thereon. The weld effected by the method of the invention may be either a spot weld or a continuous weld. Further in accordance with the structure of the invention the flux concentrating core may be on one or both sides of the materials to be welded and may be linear and perpendicular or at an angle to the members to be welded, or may be U-shaped or cup-shaped including a central post around which the coil is wrapped.

Structure and method for resistance welding with an inductively coupled

A method of and structure for high speed seam welding. The method comprises placing an auxiliary transformer between a three phase source of electrical welding energy and seam welder structure, which auxiliary transformer includes three separate primary windings connected to the separate phases of the source of welding energy, phase controlling the energizing of each separate primary winding and energizing the seam welder from the auxiliary transformer. In one embodiment, the phases of the auxiliary transformer are energized in the order of the phase of the welding energy and a delay of approximately 120.degree. of the welding energy is provided between the energizing of each auxiliary transformer winding. In another embodiment of the invention, the auxiliary transformer primary windings are energized in a first, third, second, welding energy phase order with a delay of 240.degree. of the welding energy between energizing each primary coil winding to provide a substantially 60/40, on/off auxiliary transformer energizing. The structure of the invention may include an auxiliary transformer secondary winding connected to the primary winding of a seam welder welding current transformer or a seam welder welding current transformer having a primary winding connected in parallel with one of the three primary windings of the auxiliary transformer or an auxiliary transformer including a secondary winding connected directly to the seam welder structure.

Method of and structure for high speed resistance seam welding

Structure for and method of eliminating impedance in multiphase direct current power supplies comprising connecting transformer primary windings in Y configuration with contactor structure, whereby multiple impedance paths through transformer secondary circuits are provided.

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Plymouth, MI, United States of America

John Foster Farrow