A drive mechanism comprising a guide channel and a cooperating slide shoe the which guide channel comprises a first part extending in a substantially horizontal direction configured to move the shoe on a first level and a second part extending downwardly relative to said substantially horizontal direction configured to move the shoe to a lower second level an elongate drive member is attached to the shoe and extends along the channel, substantially in parallel to the first part of the channel. At least one portion of the shoe moves relative to the remainder of the shoe so as not to interfere with the drive member when the shoe is positioned at the lower second level. The drive member is located within the vertical projection at a level above the level assumed by the lowermost part of the slide shoe when the slide shoe is positioned at the lower second level.