Abstract:
A sterile containment welding device includes a self-monitoring heater unit upstream from the space between the tube receiving channels. The wafer is positioned in the unit and mounted for movement through the unit prior to moving through the space. The self-monitoring heater unit comprises a heater which heats the wafer and a temperature sensor for monitoring the temperature created by the self-monitoring heater in a rapidly alternating sequence so that the wafer is heated to a predetermined temperature before being moved into the space and contacting the plastic tube or tubes.

Description:
BACKGROUND OF THE INVENTION 
     Sterile containment welding devices are known for connecting and disconnecting plastic tubes. Examples of such devices are found in U.S. Pat. Nos. 5,256,229, 5,279,685 and 5,397,425. In general, such devices include a pair of tube holders which would be in alignment with each other. Each of the tube holders has a base with the tube receiving channel into which a plastic tube would be placed. Each tube holder also includes a clamping jaw having a ram and anvil located above the channel. Thus, for example, when a tube is placed in the channel the clamping jaw is moved into locking engagement with the base and the anvil presses against the tube. In one practice of such devices each tube is placed in its channel in a bent condition by being bent upon itself with the bend of the tube extending outwardly from the outer edge of the channel. Thus, in a connect procedure the pair of bent ends would be disposed toward each other with each bent section in alignment with a corresponding bent section of the opposite tube holder. The connect procedure is achieved by passing a heated wafer between the two bent tube ends which causes the tube ends to melt so that a tube section from each tube can be pressed into contact with a corresponding tube section from the other tube and thereby join the two sets of tube sections together. 
     It is known to include in such devices a thermocouple which monitors the temperature of the heater device so that there is assurance that the wafer will be heated to the desired predetermined temperature. In operation when the device is actuated the heater operates continuously to raise its temperature until the desired temperature is reached. The thermocouple, which is separate from the heater, monitors the temperature rise to sense reaching the desired temperature. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide such a sterile containment welding device with a self-monitoring heater which functions not only to heat the wafer but also to monitor the heating process. 
     A further object of this invention is to provide such a self-monitoring heater unit which functions in a rapid sequence of alternatingly monitoring the heater and performing its heating function. 
     In accordance with this invention a sterile containment welding device includes a pair of alignable tube holders each of which has a tube receiving channel with the channels being spaced from each other. A wafer is provided for selective movement into the space to connect/disconnect the tube or tubes mounted in the channels and extending into the space. In accordance with this invention a self-monitoring heater unit is provided upstream from the space. The wafer is mounted for movement through the heater unit prior to movement through the space. The unit comprises a heater for heating the wafer when the wafer is disposed in the unit and further includes a temperature sensor for monitoring the temperature created by the unit. As a result, the wafer is raised to its predetermined temperature before being moved into the space. 
     In a preferred practice of the invention the heating and monitoring functions place in rapid sequence such as being a millisecond for each function. Preferably, the self-monitoring heater unit is a ribbon etched with a trace to act as a heater and which includes a thermocouple junction for the sensor. 
    
    
     THE DRAWINGS 
     FIG. 1 is a side elevational view partly broken away showing a sterile containment welding device in accordance with this invention; 
     FIG. 2 is a side elevational view of the self-monitoring heater assembly incorporated in the device of FIG. 1; 
     FIG. 3 is a exploded perspective view of the self-monitoring heater assembly shown in FIG. 2; 
     FIG. 4 is a top plan view of the self-monitoring heater unit shown in FIGS. 2-3; 
     FIG. 5 is an enlarged side elevational view showing the etching trace for the self-monitoring heater unit of FIGS. 2-4; and 
     FIG. 6 is a graph showing the sequence of operation of the self-monitoring unit of this invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to sterile containment welding devices for connecting or disconnecting plastic tubes. Such devices are known in the art. Examples are described in U.S. Pat. Nos. 5,256,229, 5,279,685, and 5,397,525, all of the details of which are incorporated herein by reference thereto. In particular, the later described self-monitoring heater unit is incorporated in the type of device shown in detail in U.S. Pat. No. 5,279,685. 
     In general, the sterile containment welding device 10 includes a base member 12 and a pivotally mounted upper member 14. The base member and upper member maybe considered as comprising a pair of tube holders each of which has a tube receiving channel 16 into which a tube or tube section 18 would be located in a known manner. The tube 18 is in a flattened condition by manipulating the handle 20 which actuates a clamping jaw 22 having an anvil 24 which is locatable over the channel 16 for pressing against the tube. The outer end of the channels are spaced from each other so that a wafer 26 shown in phantom in the right hand portion of FIG. 2 may pass through the space and heat two tube sections for welding or connect purposes or melt through a tube extending across the channels for disconnect purposes. Wafer 26 which is shown in full lines in the center of FIG. 2 is mounted in a holder 28 received a carriage connected to a drive 30 and moved by reversible motor 32 known manner in a forward direction as indicated by the arrow 34. The carriage is then returned to the start position. The wafer is heated prior to moving to the spacing to effect the connect/disconnect operation. 
     In accordance with this invention a self-monitoring heater unit 36 is provided to form the dual functions of heating the wafer and monitoring the heating temperature to assure that the wafer is heated to its desired predetermined temperature. 
     As illustrated, the self-monitoring heater unit 36 comprises a pair of spaced, parallel thermocouple ribbons 38 which are formed by having an etched trace 40 as best shown in FIGS. 3 and 5. Each thermocouple ribbon is laminated onto a thick support member 42 such as a silicone tape. In the preferred practice of this invention a flat E-type thermocouple ribbon composed of Cu/Ni and Ni/Cr (Chromel-Constantan) with the individual legs of the thermocouple sized so that the electrical resistances equilibrate out to about 5.68±10% ohm resistance. The thermocouple trace experiences a temperature rise causing a voltage change that can be measured. In accordance with this invention utilization is made of the etched trace 40 so that it also functions as a heater. The trace 40 includes a thermocouple junction 44 to permit the monitoring to take place. In this manner there is first a heating operation and then a measuring or monitoring operation. The switching takes place by appropriate electronics at speeds of milliseconds. For example, there is one millisecond of the unit 36 functioning as a heater with the next millisecond functioning as a thermocouple when the unit 36 functions as a heater. The temperature rises then for the next millisecond. There is then a monitoring of the temperature with the temperature again rising in the subsequent millisecond until the desired temperature is reached. When the desired temperature is reached, the wafer 26 is heated to that temperature by being contacted on each side by an etched trace 40. The heated wafer then moves from unit 36 to the spacing between the tube holding channels. 
     In the preferred practice of the invention the thermocouple ribbon is about 0.002 inches thick. The polarity of the thermocouple is marked by etching a hole on the constantan or negative side of the thermocouple. FIG. 4 also illustrates the positive conductor wire 47 for the electrical conductor cables 46. The cables 46 are mounted to printed circuit board 45 as best shown in FIG. 1. The type-E thermocouple ribbon is preferably laminated onto a 0.001 inch thick silicone tape. The trace art work is registered with respect to the thermocouple junction 44. The trace is then etched followed by a covered lamination of 0.001 inch thick silicone tape. 
     As shown in FIG. 3 each ribbon 38 is connected to a cable 46 at one end thereof. A leaf spring 48 is provided for each ribbon 38 to urge the two ribbons toward each other. Each leaf spring 48 is mounted in a spring clamp 50 on an insulator support 52. A pair of screws 49 extend through the holder 28 and press against each spring 48 to control the spacing between the two parallel sections of unit 36 particularly the traces 40. Screws 49 thereby assure that the spacing is sufficient to allow wafer 26 to pass between the two traces 40 and yet be close enough to assure that there rubbing contact by each side of the wafer 26 and its respective heater trace 40. 
     Wafer 26 may be of any suitable construction and preferably is of the construction shown and described in U.S. Pat. Nos. 5,525,186 and 5,397,425, the details of which are incorporated herein by reference thereto. 
     In the practice of the invention the wafer 26 would be mounted in the holder 28 between the closely spaced trace portions 40,40 of the self-monitoring heater unit 36. While the wafer is in this upstream position the unit 36 begins its rapid sequence of heating and temperature monitoring in the sequential steps illustrated in FIG. 6 until, for example, a predetermined temperature such as 300° is reached. FIG. 6 illustrates the sequence of heating and temperature monitoring to take place wherein the heating period of time (which might be considered a first fixed period of time) is nine times longer than the monitoring period of time (which might be considered a second fixed period of time). Thus, this rapid sequence permits the wafer or heat applying tool to reach a predetermined temperature in an accurate manner. Because the wafer 26 in holder 28 is in the unit 36 with each side of the wafer 26 contacted by the heater element or trace 40 of unit 36, the wafer is raised to its predetermined temperature. The wafer is removed by the carriage from holder 28 and then moved downstream in the direction of arrow 34 away from unit 36 and into the space between the tube receiving channels 16 in a known manner. 
     The present invention thus provides a combined heater and thermocouple which results in a self-monitoring heater which detects the temperature rise of its own heating elements in a rapid sequential manner to effectively heat a wafer for thereby improving the heater performance of the sterile containment welding device.