Method and an apparatus for stepwise movement of a reinforcement grid

Apparatus adapted for moving a grid forward longitudinally in stepwise fashion, with a pause between each step, through a multi-spot welding machine, said grid comprising a plurality of longitudinal rods and a plurality of transverse rods welded thereto in said welding machine, at selected spacings, said apparatus comprising

• an element adapted to engage one of said transverse rods at a starting position, to move said grid thereafter in a forward direction through a number of steps and pauses at a first mean speed, to be disengaged subsequently from said transverse rod, and following the disengagement from said transverse rod, to return to said starting position at a second mean speed higher than said first mean speed, each step in the forward direction including a movement at a forward speed, followed by a pause having a duration up to a maximum duration,
• determining means for establishing a time interval required for said element to return to said starting position at said second mean speed after having advanced an additional forward step beyond said number of steps, and having rested during said maximum pause duration,
• comparing means for comparing said time interval with the time required for said element to return to said starting position at said second mean speed following the disengagement from said transverse rod, and
• returning means for returning said element to said starting position if said time interval is determined to be greater than said maximum pause duration.