Patent ID: 7359764

Claim:
A system for positioning a pair of carriages in spaced relationship to one another, comprising: a first drive arrangement acting on a first carriage to move the first carriage along a first reciprocating path; a second drive arrangement acting on a second carriage to move the second carriage along a second reciprocating path; a first position measuring device for measuring positions of the first carriage along the first reciprocating path and for generating a first position signal indicating position of the first carriage on the first reciprocating path; a second position measuring device for measuring positions of the second carriage along the second reciprocating path and for generating a second position signal indicating position of the second carriage on the second reciprocating path; a motion detector positioned relative to the first and second reciprocating paths to generate a first reference signal as the first carriage moves past the detector and to generate a second reference signal as the second carriage moves past the detector; and electronics for receiving the first and second position signals and the first and second reference signals; acting on the first position signal and first reference signal to provide a first carriage reference position; acting on the second position signal and second reference signal to provide a second carriage reference position; comparing the second carriage reference position signal to the first carriage reference position to determine a difference there between defined as an offset, wherein the offset is selected from a plus value, a negative value or zero difference, and acting on the second drive arrangement to position the second carriage in a predetermined position on the second reciprocating path relative to the first carriage, wherein the predetermined position on the second reciprocating path is the position of the second carriage indicated by the second position signal plus the offset.