A picture changer as an auxiliary mechanism for use with and adapted to be attached on a large-size picture projector which on its upper surface is provided with a transparent projector plate through which light from a light source in the projector is transmitted, wherein said changer comprises:
- a magazine for picture plates, said magazine disposed to one side and outside one edge of said projector plate when the changer has been attached on a large size picture projector;
- in said magazine, a plurality of flat picture plates are stored in a fixed position relative to the magazine;
- said changer includes an adjusting means, with a lifting means having a lifting table upon which said magazine is removably located and positioned, provided to vertically lift and lower and selectively adjust the vertical disposition of the magazine so that any specific selected picture plate in the magazine is positioned in parallel with and slightly above the plane of the projector plate at one of the sides of the projector plate;
- a drawing means is provided to seize a selected said picture plate and pull it across and to a specific indexed position over said projector plate and also to push that selected picture plate from its position over the projector plate back into its storage position in the magazine;
- said drawing means includes an elongated bar which is parallel with the forward edges of said picture plates and adapted to be located above the plane of the projector plate and is movable perpendicular to its longitudinal dimension in a path parallel to and across the top of the projector plate;
- a pair of grip means are disposed on said bar, one grip means adjacent each end of said bar;
- each said picture plate, adjacent its forward portion being provided with a recess in each of its two opposed side edges, into which recesses said draw bar grip means are interfitted by movement of said magazine perpendicularly to the planes of the picture plates whereby a selected picture plate is moved to a position at which it is seized on two edges by said grip means;
- spaced apart indexing guide means on the changer;
- spaced apart cooperating index means on the front edge of each picture plate adapted to abut said indexing guide means and accurately locate said picture plate in a projecting position in said changer above the projector plate;
- said adjusting means comprises an electric motor and rotatable drive shaft for driving the lifting means and therewith for moving the lifting table and magazine to a desired position;
- a revolution indicator provided to indicate the number of revolutions, of said rotatable shaft, said revolution indicator being adapted to emit and transfer pulses related to said shaft revolution;
- control means include an electronic computer receiving said pulses and an electronic memory unit with electronic circuits for storing a figure representative of a predetermined plate location in said magazine said computer being capable to emit a signal when said indicator has emitted the number of pulses corresponding to said stored figure, which signal causes said motor to stop;
- and means with a reading fork are provided for reading a predetermined height position of the magazine, said fork sensing said height positions and adapted to emit an impulse to said computer when said height prevails, by which impulse the computer is set for a value predetermined for said height position.