Power control and line voltage monitor/compensator for resistance spot welding machines
First Claim
1. A method for pulse-by-pulse monitoring of variations in multi-phase AC input line power applied as sequential power pulses to a load through selectively triggered thyristor type devices of a power control, comprising the steps of:
- monitoring a function of each of the multi-phase AC input line signals to the thyristor type devices, the function comprising one of current and voltage;
synthesizing from the monitored function, during the operation of the thyristor type devices, a first replica signal replicating the composite function passed to the load by the thyristor type devices, the commutation effect of the thyristor type devices being replicated in synthesizing the first replica signal; and
processing the first replica signal to produce an independent measurement of a circuit parameter for each individual power pulse.
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Abstract
A programmable power control and line voltage monitoring/compensation system for resistance spot welding machines of varying configurations provides maximum time for computer calculation of SCR triggering times and compensates in real time for these input power line fluctuations that affect the welding operation. The power control employs a single programmable delay element, the delay time of which is set while the delay is timing out to generate SCR trigger pulses. The commutation effect in three phase welding machine configurations is taken into account by the power control in determining trigger times. The line monitor synthesizes replica signals of both the primary voltage and current transmitted by the SCRs and processes these replica signals to provide various circuit parameters which can be used as feedback to compensate for only those line variations which affect the welding process.
19 Citations
33 Claims
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1. A method for pulse-by-pulse monitoring of variations in multi-phase AC input line power applied as sequential power pulses to a load through selectively triggered thyristor type devices of a power control, comprising the steps of:
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monitoring a function of each of the multi-phase AC input line signals to the thyristor type devices, the function comprising one of current and voltage; synthesizing from the monitored function, during the operation of the thyristor type devices, a first replica signal replicating the composite function passed to the load by the thyristor type devices, the commutation effect of the thyristor type devices being replicated in synthesizing the first replica signal; and processing the first replica signal to produce an independent measurement of a circuit parameter for each individual power pulse. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Apparatus for pulse-by-pulse monitoring of variations in AC input line power applied as sequential power pulses to a resistance spot welding machine through selectively triggered thyristor type devices of a power control, comprising:
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monitoring means for monitoring the voltage on all AC input lines to the thyristor type devices; synthesizing means for synthesizing from the monitored voltage, during the operation of the thyristor type devices, a first replica signal replicating the composite voltaged passed to the welding machine by the thyristor type devices; and processing means for processing the first replica signal to produce an independent measurement for each individual power pulse of at least one of the following;
average voltage squared and average voltage. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A programmable power control and line voltage compensation system for generating and supplying trigger pulses to thyristor type devices of a resistance spot welding machine to produce a desired percent heat while compensating for transmitted variations in AC input line power to said machine, comprising:
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line synchronization means for generating a reference signal that is phase synchronized with the frequency of an AC input line signal to said thyristor type devices; programmable delay means for receiving said reference signal and a timing signal representative of trigger times for said thyristor type devices and producing trigger pulses therefrom, the delay means having a programmable delay time which is sequentially set equal to said trigger times while the delay is timing out; pulse directing means for directing said trigger pulses to appropriate thyristor type devices to be triggered; monitoring means for monitoring the voltage of AC input line signals to the thyristor type devices; synthesizing means for synthesizing from the monitored voltage a first replica signal synchronized with the operation of the thyristor type devices and replicating the composite voltage transmitted to the welding machine by said devices; processing means for processing the first replica signal to produce an independent measurement of a feedback parameter for each individual power pulse transmitted by the thyristor type devices; and computer means for receiving a desired percent heat command and responsive to the measurement of said feedback parameter for determining said triggering times, for generating and providing said timing signal to the programmable delay means and for controlling the pulse directing means, and wherein the system is programmable to operate with single phase configured and multi-phase configured welding machines, and wherein said computer means determines the trigger times as a linear function of the maximum heat actually deliverable by the welding machine taking into consideration the commutation effect of the thyristor type devices in multi-phase configurations, whereby the system affords maximum time for determination of said trigger times and adjusts the trigger times to compensate for only those line variations which would affect the welding process.
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24. A power control for single phase and multiple phase resistance spot welding machines of various types, the power control serving to trigger on thyristor type devices to selectively apply input line signals through said thyristor type devices to a spot welding machine of a specified type in order to produce a desired percent of the maximum heat available from the specified type of welding machine, comprising:
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computer means for receiving desired percent heat commands and converting said commands into corresponding trigger times, said computer means comprising means for calculating said trigger times as a linear function of the maximum heat actually deliverable by a welding machine of a specified type taking into consideration the commutation effect of the thyristor type devices in multiple phase configurations; synchronization means for generating a reference signal that is phase synchronized with the frequency of an input line signal to the thyristor type devices; single programmable delay means for receiving and employing said reference signal and signals from said computer means representative of said trigger times to produce trigger pulses for all of the thyristor type devices; and pulse directing means under control of said computer means for directing said trigger pulses to appropriate thyristor type devices to be triggered according to the specified type of welding machine. - View Dependent Claims (25, 26, 27, 28, 29)
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30. A programmable power control applicable, without hardware modification, to a single phase and to a variety of multiple phase configured resistance spot welding machines wherein trigger pulses at firing times determined in accordance with a specified welding machine configuration are generated and supplied to thyristor type devices to provide a desired percent heat, comprising:
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single programmable delay means for generating in succession all trigger pulses for the thyristor type devices for any specified machine configuration; and pulse directing means for receiving all of the trigger pulses from said delay means and for directing successive pulses to the thyristor type devices in a sequence correlated to a specified welding machine configuration. - View Dependent Claims (31, 32)
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33. A method of selectively controlling the power provided by substantially sinusoidal input multi-phase signals passed by thyristor type devices to a multi-phase resistance spot welding machine during a single cycle, comprising the steps of:
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determining appropriate firing times for respective thyristor type devices taking into account the commutation effect of such devices; converting said firing times to successive specified corresponding count values; initiating incremental counting by an upcounter upon the occurrence of a zero crossing of an input phase signal; and comparing the incrementing count of said counter with the successive specified count values and providing a trigger pulse to the respective thyristor type device when the count of the upcounter reaches the corresponding count value.
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Specification