Patent GB-973043-A (GB)
Title: Electrical timing apparatus especially for optical projectors
IPC: D06F39/00
Filed: 1962-03-12
Abstract: 973,043. Control systems for optical projectors; thermal switches. AGFA A.G. March 12, 1962 [March 14, 1961], No. 9482/62. Headings H2B and H2H. Control systems for optical projectors.-In an optical projector having a slide-changing mechanism operated by an electromagnet energized intermittently by a timing device including a bimetallic switch, the arrangement is such that the heating winding for this switch is deenergized during energization of the electromagnet to reduce the size of the supply transformer, whose rating is determined by that of the electromagnet. The components of the timing device are mounted in a common housing, Figs. 1 and 2 (not shown), and are connected as shown in Fig. 3 to the sockets 1, 2, 3 of an adaptor 7 located in the housing and having pins engaging a socket 27 on the projector, Fig. 4. The sockets 1, 2, 3 of member 27 are connected to a circuit comprising the supply transformer 32 in whose magnetic field lies the armature of a continuously-running fan motor 35, which drives the slide-changing mechanism 38 through a coupling 37 engageable by the electromagnet 36, a normally-open switch 39 being closed during a slide-changing operation. To initiate a working cycle, the connections between sockets 1, 2, 3 of members 7, 27 are completed, whereupon current from transformer secondary 31 passes through a slow-release relay 8, thus closing contacts 8a, 8b, and through a bimetallic strip 11 and its heating winding 13, the free end of the strip 11 normally engaging a spring contact 18 and being secured to an overcentre snap-action spring, Fig. 1 (not shown). Heating of the strip 11 causes closure of contacts 15, 23 and opening of contacts 11, 18, the latter action de-energizing members 8, 13 and the former action energizing the electromagnet 36 through contacts 8a, 8b which remain closed for a short time due to the discharge of capacitor 10. Thereafter the electromagnet 36 is energized through the switch 39 until the slidechanging operation is completed, a further operation being initiated by cooling of the strip 11, the time of which is determined by adjustment of the contact 23. A working cycle may be initiated by a remote control switch and cable connecting sockets 2 of members 7, 27, a plug attached to this cable co-operating with the adaptor 7, Fig. 2 (not shown). This plug may have pins co-operating only with sockets 2, 3 or may have further pins co-operating with sockets 4, 5, Fig. 4, so that, by means of a changeover switch attached to the cable, a motor 41 may be run in opposite directions for focusing the projector lens. The remote control may be effected by a high frequency device. Contact 15 may be omitted so that strip 11 cooperates directly with contact 23 and is connected to the socket 2, contact 18 then lying between the relay 8 and winding 13. The slide changing operation may be manually controlled by a switch (not shown) in parallel with the switch 39. Thermal switches.-A timing device for intermittently actuating the slide changing mechanism of an optical projector includes a bimetallic strip 11 having insulating sleeves 12, 14 carrying a heating winding 13 and a contact 15, the free end of strip 11 normally engaging a spring contact 18 and being secured to one end of an over-centre snap-action spring 16. When winding 13 is energized, strip 11 bends until it reaches the over-centre position of spring 16, whereupon the latter snaps over to engage contact 15 with a contact 23 integral with a pivoted adjustable lever 22. Contact 18 follows the strip 11 to the over-centre position before disengagement, and the cooling period of the strip may be set by the lever 22. The components of the device are mounted on an insulating base 6 carrying printed circuit connections and enclosed in a housing, Fig. 2 (not shown). By suitable alteration of the circuit connections contact 15 may be omitted so that strip 11 co-operates directly with the contact 23.