| 摘要 |
1487482 Seaming non-metallic sheet material PACKAGE MACHINERY CO 3 Jan 1975 [10 Jan 1974] 249/75 Heading B5K [Also in Divisions G1 G3 H3 and B8] Apparatus for monitoring the seals made by a packaging machine which forms pouches from a strip of fusible material, fills each pouch and seals it, comprises means for measuring a sealing parameter, e.g. temperature, pressure, and comparing it with preset limits. As shown (Figs. 1, 2), a film strip F of polyethylene is fed on to a tube 12 with an overlap which is sealed by a heater 14, and drawn between two jaws 16, 18 which are periodically brought together by a pneumatic device 20 to clamp the film between heaters 26, 28 and produce two seals across the film. The lower seal closes a lower pouch P which has been supplied with an appropriate quantity of a filling material via inner tube 40, and this pouch is severed by a heating current through wire 32. The upper seal forms the bottom of the next pouch. The quality of the transverse seals is determined by measuring the temperature of the sealing operation by thermocouple 50, and comparing it with preset upper and lower limiting values, to operate an alarm or reject device if the temperature during sealing is outside the limits. Measurements are made at a predetermined instant in the process cycle, established by an electronic timing circuit. The temperature sensed by thermocouple 50 may be used retroactively to control the current supplied to the heaters 26, 28 from A.C. source 130 (Fig. 7) by varying the phase angle of a controller 132. The amplified signal from sensor 50 is fed via photodiode 184 and phototransistor 186 to the controller 132 in parallel with temperature-adjust potentiometer 182. An increase in the sensed temperature reduces the output from diode 184, increases the impedance of transistor 186 and reduces the power supplied to the heaters 26, 28. The transistor 186 may be shut off after a number of sealing operations set up on counter 190. In an alternative arrangement (Fig. 6) the total energy fed to the heating elements 26, 28 during each sealing operation is measured, as representing the quality of the seals. The heaters are energized from A.C. source 130 through controller 132, by amplitude or phase control. The rectified heating current is averaged by components 136-140 to trigger an FET 150, causing a capacitor 152 to be charged during the conducting intervals. The resulting voltage on capacitor 152 at the end of a sealing operation is proportional to the total energy fed to the heaters 26, 28 during the sealing. Between successive operations a switch 164 is closed to cause transistor 166 to conduct and discharge capacitor 152. The parameter to be sensed for monitoring the seals may alternatively be the pressure exerted by the jaws 16, 18, measured by strain gauges 120, 122 mounted on the fixed jaw 18. |
