Apparatus for controlling the heating current for welding thermoplastic synthetics

Claim 2

In apparatus according to claim 1, said current control means comprising control transistors connected in parallel relation to each other and in series relation to said load member, said control transistors having respective base electrodes, said circuit means comprising a regulating transistor having a base circuit connected to said photoresistor and having an output circuit connected to said base electrodes for controlling said control transistors to regulate said load current.

Claim 3

Apparatus for controlling the heating current for welding of thermoplastic parts by heat and pressure with the aid of an interposed heater strip member traversed by the current during welding and remaining embedded in the weld, comprising feed-voltage supply means, a load circuit serially including said welding heater strip member when in operation and connected to said supply means for passing heating current through said member, current control means connected in said load circuit and having means for regulating said heating current to maintain it substantially at a predetermined value independently of the feed voltage and the resistance of said member, and a timing monitor connected to said current control means and having sequencing switch means for incrementally reducing said heating current in accordance with a given time sequence and for discontinuing said load current at the termination of said sequence, said heater strip member being of uniform structure and having a uniform ohmic resistance R per unit length so that the amount of heat required per unit length to produce the weld is determined by the power loss I2R and therefore depends only upon the adjustment of the current I thereby being independent of the length and total resistance of said heater strip.

Claim 4

In apparatus according to claim 4, said monitor comprising a pulse generator constituted by a multivibrator network, and a pulse-counting chain network connected to said multivibrator network and having respective progressive counter stages determining the amount of current flowing through said heating member.

Claim 5

In apparatus according to claim 5, said pulse-counting network comprising chain-connected bistable stages having respective thyristors of which each has a firing electrode, said pulse generator having a pulse output line, coupling capacitors connecting said line to said respective firing electrodes for sequentially switching said thyristors to the ON state upon arrival of sequential pulses respectively.

Claim 6

In apparatus according to claim 5, said pulse generator comprising a thermistor subject to ambient temperature and connected in said multivibrator network for varying the pulse sequence of said multivibrator network so as to secure at lower ambient temperatures a slower pulse sequence than at high temperatures.

Claim 7

Apparatus according to claim 2, comprising condition-sensing control means responsive to departure of said heating current from a given intensity range.

Claim 8

Apparatus for regulating an electric current flowing through a load, comprising a load circuit including a load member whose current is to be regulated, feed-voltage supply means connected to said load circuit for passing said current through said member, current control means connected in said load circuit for controlling said current, said current control means comprising control transistors connected in parallel relation to each other and in series relation to said load member, said control transistors having respective base electrodes, a voltage-drop resistor serially connected in said load circuit to provide a pilot voltage indicative of said load current, a light source connected to said resistor to be controlled in dependence upon said pilot voltage, a voltage divider having a photoresistor subjected to the light of said source, constant direct-voltage means connected to said voltAge divider whereby said photoresistor furnishes a signal voltage, and circuit means connecting said photoresistor to said current control means for controlling said control means to regulate said load current in dependence upon said signal voltage, said circuit means comprising a regulating transistor having a base circuit connected to said photoresistor and having an output circuit connected to said base electrodes for controlling said control transistors to regulate said load current.

Claim 9

Apparatus for controlling the heating current for welding of thermoplastic parts by heat and pressure with the aid of an interposed heater strip member traversed by the current during welding and remaining embedded in the weld, comprising feed-voltage supply means, a load circuit serially including said welding heater strip member when in operation and connected to said supply means for passing heating current through said member, current control means connected in said load circuit and having means for regulating said heating current to maintain it substantially at a predetermined value independently of the feed-voltage and the resistance of said member, and a timing monitor connected to said current control means and having sequencing switch means for incrementally reducing said heating current in accordance with a given time sequence and for discontinuing said load current at the termination of said sequence.

Claim 10

Apparatus for controlling the heating current for welding of thermoplastic parts by heat and pressure with the aid of an interposed heater strip member of arbitrary length traversed by the current during welding and remaining embedded in the weld, comprising feed-voltage supply means, a load circuit serially including said welding heater strip member when in operation and connected to said supply means for passing heating current through said member, and current control means connected in said load circuit and having means for regulating said heating current to maintain it substantially at a predetermined value independently of the feed-voltage and the resistance of said member, said heater strip member being of uniform structure and having a uniform ohmic resistance R per unit length so that the amount of heat required per unit length to produce the weld is determined by the power loss I2R and therefore depends only upon the adjustment of the current I and is independent of the length and total resistance of said heater strip.

Claim 11

In apparatus according to claim 11, said monitor comprising a pulse generator constituted by a multivibrator network, and a pulse-counting chain network connected to said multivibrator network and having respective progressive counter stages determining the amount of current flowing through said heating member.

Claim 12

In apparatus according to claim 12, said pulse-counting network comprising chain-connected bistable stages having respective thyristors of which each has a firing electrode, said pulse generator having a pulse output line, coupling capacitors connecting said line to said respective firing electrodes for sequentially switching said thyristors to the ON state upon arrival of sequential pulses respectively.

Claim 13

In apparatus according to claim 12, said pulse generator comprising a thermistor subject to ambient temperature and connected in said multivibrator network for varying the pulse sequence of said multivibrator network so as to secure at lower ambient temperatures a slower pulse sequence than at higher temperatures.