Dispensing – Automatic control – Temperature responsive or soluble controller
Reexamination Certificate
1999-10-15
2001-03-20
Derakshani, Philippe (Department: 3754)
Dispensing
Automatic control
Temperature responsive or soluble controller
C063S033000, C063S033000
Reexamination Certificate
active
06202892
ABSTRACT:
TECHNICAL FIELD
A method and apparatus for delivering melted material. More particularly, the apparatus is a glue gun utilizing a method of delivery of molten glue without unwanted drips and at a controlled temperature.
BACKGROUND OF THE INVENTION
Prior art devices have been utilized for heating and dispensing materials, such as for heating a solid material until it melts and then dispensing the material as a liquid. For example, hot glue guns are used for heating an end of a solid glue stick to a transition temperature at which the glue is liquified and then dispensing the melted glue through a dispensing orifice. Typically, a housing is provided having an interior flow path through which the material is pushed as it is heated. Resistance heating elements are commonly used. The resistance heating elements have been mounted to the housing outside of the flow path, and often outside of the housing.
Other devices have utilized induction heating to heat materials for dispensing. A housing is usually provided having an interior flow path through which the material is pushed as it is heated. An electromagnetically heated susceptor is located either directly in or immediately adjacent to the material flow path. Induction coils have been mounted outside of the housing for inducing eddy currents to flow within the susceptors to generate heat for transferring to the materials. Often an external shroud is provided around the induction coil to protect an operator.
A difficulty with prior devices is that once the meltable materials have been melted and dispensed, it is difficult to cease flow of the meltable material without additional and unwanted drips emerging from the nozzle. The additional flow is partially due to a large orifice in the nozzle and to an area of high pressure resulting from compression of the meltable material from the pusher used to force a material towards the heating elements.
SUMMARY OF THE INVENTION
A method and apparatus are provided for heating and dispensing a melted material. A glue gun has a cylindrical body with a trigger mechanism provided on an under side of the body. A motor is located in the interior of the body at a rearward end of the cylindrical body. A gear head is operatively connected to a forward end of the motor. An externally threaded driver screw is rotationally connected to the gear head. A pusher is slidably received within the interior of the cylindrical body and is movable relative to the forward end of the cylindrical body. The pusher is made up of an internally threaded cylinder that receives the driver screw and has an end surface on its forward end that engages a meltable material such as glue, preferably in stick form. The pusher is used to advance the meltable material toward the forward end of the body. The pusher retracts when the a stroke limit of the pusher is reached and the meltable material is substantially exhausted.
A nose assembly is positioned on the forward end of the cylindrical body and is made up of a conical housing, a conical inductor, a conical susceptor, and a nozzle positioned within a central orifice of each of the conical members of the nose assembly. The inductor is preferably a coil that surrounds the susceptor for heating the susceptor. The nozzle permits a flow of a meltable material through a plurality of peripheral passages. The peripheral passages are sized to permit a flow of meltable material under pressure but not to permit a flow of material when not under pressure.
The induction heated system of the invention is dripless and operates without a valve for several reasons. A main reason is that the motor automatically retracts the pusher a slight increment when the motor is turned off, which relieves static pressure on the elastic zone. The expansion of the compressed zone moves the stick back instead of pushing liquid material downstream. Second, the initial start up heat mass is maintained to be as low as possible to shorten the time from trigger pull to material delivery, preferably less than two seconds. Third, the latent heat mass is minimized to diminish “off” cycle melting at the stick melt phase.
An electrical cable connects the inductor with a power source. A PC board has a control circuit to control the advancing and retracting of the pusher and for controlling the temperature of the inductor by regulating the flow of power to the inductor.
The control circuit also automatically detects whether a newly loaded stick of meltable material, such as glue, is positioned within the cavity of the cylindrical body. If so, the pusher is advanced to lock the stick in the cavity. The control circuit will allow full retraction of the pusher only after the chamber is empty or when the pusher is at full stroke. The control circuit automatically detects when the pusher is at full stroke and ceases delivery of power to the inductor and returns the pusher to the reload position. Additionally, the control circuit is designed to determine whether an amount of current is being used that indicates a resistance to pusher movement provided by a loaded stick and whether the thermocouple is in operation. If either of these conditions is not satisfied, then power is automatically shut off to the inductor. Otherwise, the inductor is heated and the pusher is advanced to force liquid meltable material out of the nozzle. If the temperature of the inductor is above a target temperature, then power will be shut off to the inductor and cycled on and off to maintain the approximate target temperature. When the trigger is released, power is shut off to the inductor and the pusher is retracted a slight increment to relieve static pressure on the elastic zone.
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Bracewell & Patterson
Bradley James E.
Derakshani Philippe
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