RF generator for plastic tubing sealers

Apparatus for welding plastic material placed between a pair of electrically conducting jaws movable to compress the plastic material therebetween, said apparatus comprising in combination:

• a) means for generating an RF signal;
• b) means for detecting a predetermined impedance across said pair of electrically conducting jaws;
• c) means for transmitting the RF signal across said pair of electrically conducting jaws and through the plastic material placed therebetween to heat and melt the plastic material as a function of changes in said predetermined impedance across said pair of electrically conducting jaws;
• d) means for automatically terminating operation of said generating means in response to said predetermined impedance across the pair of electrically conducting jaws;
• and
• e) a source of direct current power for energizing said generating means, said transmitting means and said terminating means.

A tubing sealer for applying RF energy across a pair of electrically conducting jaws to compress, melt and weld a length of tubing placed therebetween, said tubing sealer comprising in combination:

• a) means for reducing voltage level of the RF energy applied across the pair of electrically conducting jaws in response to melting of the tubing;
• b) means for sensing the reduced voltage level and for providing an output signal in response to the reduced voltage level;
• and
• c) means responsive to the output signal for terminating further application of RF energy across the pair of electrically conducting jaws.

Apparatus for melting and welding plastic material placed between electrically conductive first and second jaws for compressing the plastic material, said apparatus comprising in combination:

• a) means for generating an RF output signal across the first and second jaws to melt the plastic material in response to movement of the first jaw to compress the plastic material;
• b) means for detecting an impedance across said first and second jaws;
• and
• c) means for automatically terminating operation of said generating means in response to a reduction of said impedance between the first and second jaws due to melting of the plastic material.

Apparatus for melting and welding plastic material placed between a pair of electrically conductive jaws for compressing the plastic material, said apparatus comprising in combination:

• a) means for generating an RF output signal across the pair of electrically conductive jaws to melt the plastic material in response to movement of the pair of electrically conductive jaws to compress the plastic material;
• b) means for terminating operation of said generating means in response to a reduction of impedance between the pair of electrically conductive jaws and indicative of a predetermined state of weld of the plastic material;
• c) means for sensing electrical arcing across the pair of electrically conductive jaws;
• and
• d) means responsive to said sensing means for inhibiting generation of the RF output signal.

Apparatus for sealing tubing placed between electrically conductive first and second jaws one of which is movable to compress the tubing, comprising in combination:

• a) an rf generator coupled to apply an rf voltage across the first and second jaws;
• b) a switch responsive to movement of the first jaw;
• c) a control circuit responsive to said switch and coupled to a start input of said rf generator and operative to start said rf generator in response to the movement of the first jaw;
• and
• d) a sensor circuit coupled to the first jaw and operative to
• (1) sense a decrease of the rf voltage occurring as a result of collapse of the tubing under compression between the first and second jaws caused by melting of the tubing by rf energy delivered via the first and second jaws to the tubing, and
• (2) produce a stop signal in response to said decrease of the rf voltage,
• e) said control circuit including a second circuit coupled to receive the stop signal and operative to stop said rf generator to thereby prevent further heating and melting of the tubing.

A method for sealing tubing placed between electrically conductive first and second jaws, the first jaw being moveable to compress the tubing against the second jaw, the method comprising the steps of:

• a) applying force to move the first jaw toward the second to compress the tubing;
• b) starting operation of an rf generator in response to the moving first jaw;
• c) applying an rf signal across the first and second jaws in response to the operation of the rf generator to heat the tubing under compression toward its melting point;
• d) detecting an onset of melting of the tubing by sensing a change in the rf signal resulting from a change of impedance between the first and second jaws as the first jaw moves toward the second jaw as a result of the onset of melting;
• e) producing a stop signal a predetermined time after the sensing;
• and
• f) immediately stopping the operation of the rf generator in response to the stop signal.

A method for controlling melting of plastic placed between first and second electrically conductive jaws one of which is moveable to compress the plastic, the method comprising the steps of:

• a) applying force to move the first jaw toward the second to compress the plastic;
• b) starting operation of an rf generator in response to the movement of the first jaw;
• c) applying an rf signal across the first and second jaws in response to the operation of the rf generator to supply rf energy to heat the plastic under compression toward its melting point;
• d) detecting an onset of melting of the plastic by sensing a change in the rf signal resulting from a change of impedance between the first and second jaws as the first jaw moves toward the second jaw as a result of the onset of melting;
• e) producing a stop signal a predetermined time after the sensing;
• and
• f) immediately substantially reducing the amount of rf power supplied in response to the stop signal.