Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
1999-08-31
2001-09-25
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S085190, C219S086510, C219S089000
Reexamination Certificate
active
06294750
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to pneumatically actuated resistance weld heads and reflow solder heads. More particularly, the invention relates to weld and reflow solder heads having an automatic cutoff of pressurized gas in a pneumatic cylinder when a desired weld force between an electrode and workpiece is attained.
For convenience, hereinafter the terms “weld” and “welding” shall refer to both resistance welding and reflow soldering systems and operations.
Air-actuated weld heads typically include an air cylinder which controls the upward and downward motion of one or more electrodes used to weld or reflow solder a workpiece. Such weld heads are adjustable and may be adapted for welding different types of workpieces.
Typically, different welding applications require different welding parameters. These parameters include the duration and magnitude of electrical weld energy, and the weld force, which is the force exerted on the workpiece by the electrode.
Typically, in known air-actuated weld heads, a maximum air pressure in the air cylinder is set separately from the weld force, which is usually set by precompressing a spring in the weld head connected between the air cylinder and the electrode. One problem associated with this manner of setting up the weld head for a new welding application is that, if set incorrectly, the air cylinder may continue to exert pressure on the electrode after the desired weld force has been attained resulting in excessive weld force.
In most weld heads, a force firing switch is operatively connected to the spring for sensing when the desired weld force is reached; that is, when the force applied by the air cylinder overcomes the precompression spring force. When the force firing switch activates in response to a desired weld force, it signals a microcontroller in a welding power supply to supply electrical current to the electrode(s) to initiate welding. The air cylinder is preset by manually setting pressure regulators on the air cylinder to a maximum pressure at which the force firing switch just activates. This is usually determined by first presetting the spring to the desired weld force and then performing a “dry run” with the air cylinder set to a pressure judged to be slightly above the target maximum pressure in the air cylinder corresponding to the desired weld force. During the dry run, the operator must first observe actuation of the force firing switch, note the pressure in the air cylinder, and then set the air cylinder pressure regulator for precisely that pressure. This procedure must be repeated any time a welding application requires a different weld force.
Such manual operation invites human error. This may occur in the form of an inaccurate initial setting, or by the operator forgetting to reset the air pressure in the cylinder for a new welding application. Such inaccurate settings can result in either an excessive or inadequate weld force, resulting in damaged welds or insufficient pressure to activate the force firing switch.
Furthermore, pressure settings in the air cylinder valves may drift, requiring subsequent adjustments to maintain the desired weld force. Such valve drift may go unnoticed through several welding operations, increasing the potential for unsatisfactory welds. Also, such continual adjustment increases the potential for human error.
SUMMARY OF THE INVENTION
A weld head or reflow solder head according to one embodiment of the invention includes an electrode controlled by a pneumatic cylinder, the pneumatic cylinder operating to force the electrode onto the workpiece and to retract the electrode off from the workpiece. For convenience, hereinafter the terms “weld” and “welding” shall refer to both welding and reflow soldering systems and operations. The pneumatic cylinder includes a first gas line and a second gas line. When pressing the electrode onto the workpiece, the first gas line supplies pressurized gas, preferably air, to the pneumatic cylinder and the second line exhausts the pressurized gas from the pneumatic cylinder. The weld head also includes a switch, having an on state and an off state, which is switched on when the electrode presses onto the workpiece with a desired weld force and means for simultaneously supplying electrical energy to the electrode for welding when the switch is on. The weld head also includes means for sealing the first gas line and the second gas line when the switch is on, thereby maintaining a desired pressure in the pneumatic cylinder.
In an alternate embodiment, the weld head includes a hydraulic cylinder instead of a pneumatic cylinder. The hydraulic system of the alternate embodiment operates in a manner analogous to that of the above described pneumatic system as the same principles of fluid dynamic apply.
One embodiment of a pressure regulator system according the present invention comprises a switching valve. The switching valve includes four ports: an inflow port; an exhaust port; a first gas line port; and a second gas line port. Attached to each of the gas line ports is a two-way valve. The pressure regulator system includes a valve sensor for determining an activated state of a weld force sensor incorporated in the weld head. The pressure regulator system also includes means for substantially simultaneously closing and sealing the two-way valves on the first gas line port and the second gas line port when the sensor determines an activated state of the weld force sensor.
According to another embodiment of the invention, a weld force in a pneumatically actuated welding system is controlled by performing the following steps which include moving an electrode onto a workpiece with a pneumatic cylinder and forcing the electrode onto the workpiece. Once a desired weld force is sensed between the electrode and the workpiece, the air supplied to and exhausted from the pneumatic cylinder is blocked. In this manner, the desired pressure in the pneumatic cylinder corresponding to the desired weld force is maintained in the cylinder during the welding operation.
By automatically cutting off the gas flow to the pneumatic cylinder when the desired weld force is attained in each welding operation, the above described embodiments of the invention provide several advantages over known weld heads. These advantages include eliminating human error due to inaccurate presetting of the maximum gas pressure in the pneumatic cylinder and automatic drift of the valve settings on the pneumatic cylinder, thereby improving the repeatability of the welding operation.
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Christie Parker & Hale LLP
Shaw Clifford C.
Unitek Miyachi Corporation
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