Projection unit for a light permeable original in a copying machine

A projection unit which is mounted in a copying machine and used to project an image of a light permeable original onto a prescribed exposure point on a photosensitive material, said projection unit comprising:

• a light source for exposure which is installed in a box;
• an original holding means which holds the original in a prescribed position with respect to said light source for exposure and said photosensitive material, and is disposed movably in said box so that the image of the original held in said original holding means is scanned in a prescribed direction with respect to the photosensitive material;
• a driving means for moving said original holding means in the scanning direction;
• a transmission means which is provided between said original holding means and said driving means, and is capable of moving between an engaged position in that said transmission means is coupled to said original holding means and said driving means so as to transmit power of said driving means to said holding means and a disengaged position in that said transmission means is not coupled to said original holding means and said driving means;
• and
• a switching means for putting said transmission means in the engaged position or disengaged position.