The cover is divided into green and violet halves in order to reduce its occupied space in moving or to ease the manufacture.
The green half has two pink rollers rolling in blue runway.
The violet half has a pink roller rolling and a pink slider sliding in the runway.
Yellow conrod has revolute joints with the two halves and the slider. Length of the conrod is reduced to minimum due to the said reason.
Brown motor fixed to the slider has cyan pinion which engages with orange rack fixed to the runway. So driving force from the motor is applied to the slider. The obtuse angle of blue runway is a key factor and it should be as large as possible to ease the motion.
Because of the moving motor, electric cable connected to it must be movable.
The mechanism is cut off half for easy understanding.