Side sealing mechanism for a packaging machine

Mechanism for sealing together two face-to-face strips of heat-sealable material at longitudinally spaced positions along the strips as the latter are advanced with continuous motion along a predetermined path, one of said strips having targets spaced longitudinally therealong with the spacing between successive targets being approximately equal, said mechanism comprising a frame, a drum mounted on said frame to rotate about a predetermined axis, a plurality of heat sealing bars carried by and spaced circumferentially around said drum, one of said strips engaging said sealing bars as said strips are advanced along said path, means mounting said sealing bars on said drum to move radially inwardly and outwardly relative to the drum to thereby enable the radial position and the circumferential spacing of said sealing bars to be changed, an actuator connected to said sealing bars and rotatable with said drum, said actuator also being rotatable relative to said drum and being operable when so rotated to move said sealing bars radially inwardly or outwardly relative to said drum, means for detecting said targets and for producing command signals indicative of the spacing between said targets, means for detecting said sealing bars and for producing feedback signals indicative of the circumferential spacing of said sealing bars, means for comparing said command and feedback signals, and power-operated means responsive to said comparing means and operable to rotate said actuator relative to said drum when the spacing between said sealing bars differs from the spacing between said targets.