US3742295A

US3742295A - Lighting system in copying apparatus

Info

Publication number: US3742295A
Application number: US00125033A
Authority: US
Inventors: Y Irie
Original assignee: Minolta Co Ltd
Current assignee: Minolta Co Ltd
Priority date: 1970-03-30
Filing date: 1971-03-17
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26
Also published as: DE2115028A1

Abstract

A lighting system comprises a triac included in the electric circuit of an exposure lamp in series therewith and a trigger circuit for triggering the triac into conduction at a small conduction angle simultaneously when a main switch is turned on and triggering the triac into conduction at a large conduction angle simultaneously when a start switch is turned on. The system protects the contacts and other switching elements of switches from possible damage to be caused when the exposure lamp is turned on and permits a short period of exposures.

Description

United States Patent 1 1 [111 3,742,295

lrie June 26, 1973 [541 LIGHTING SYSTEM IN COPYING 3,310,687 3/1967 Howell 307/252 B APPARATUS 3,103,618 9/1963 Slater 307/252 N X [75] inventor: Yutaka lrie,Toyokawa,Japan FOREIGN PATENTS OR APPLICATIONS 753,047 2/1967 Canada 355/69 [73] Assignee: Minolta Camera Kabishiki Kaisha, OTHER pUBuCATlONS I Minamiku, OSakaJaPa" GE SCR Manual 4th Edition 1967; pages 144-145. [22] Filed: Mar. 17, 1971 Primary Examiner-Rudolph V. Rolinec [2]] Appl' N 125,033 Assistant ExaminerMarvin Nussbaum Attorney-Stanley Wolder Foreign Application Priority Data Mar. 30, 1970 Japan /26745 [57] ABSTRACT A lighting system comprises a triac included in the elec- [52] US. Cl... 315/194, 315/200 R, 315/208 R, tric circuit of an exposure lamp in series therewith and r v 355/69 a trigger circuit for triggering the triac into conduction [51] Int. Cl. H05b 37/02 at a small conduction angle simultaneously when a [58] Field of Search ..3l5/246-249, 200, 206, main switch is turned on and triggering the triac into 194; 307/252 B, 305; conduction at a large conduction angle simultaneously 314 135; 321 45 355 9 57 when a start switch is turned on. The system protects the contacts and other switching elements of switches [56] References Cited from possible damage to be caused when the exposure UNITED STATES PATENTS 1:11:22; is turned on and permits a short period of expo- 3,446,991 5/1969 Howell 307/252 B 3,300,711 1/1967 Duncan 315/71 x 5 Claims, 11 Drawlng Figures 3,328,676 6/1967 Slater 307/252 N X 3,573,543 4/1971 Grindstaff 315/194 PATENIEDwnzswn 3.742 295 SHEEI 1 0F 3 FlGla CL FlGlb PRIOR ART W PR'OR ART START COIL START S SWITCH SWITCH c A.C.

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A crazy LIGHTING SYSTEM IN COPYING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to a lighting system in copying apparatus, more particularly to a system for lighting an exposure lamp in copying apparatus.

The switching of an exposure lamp in copying apparatus is generally controlled by the sequential steps of copying operation such as setting or insertion of an original document, feeding of photosensitive paper or the like. Since the filament of the exposure lamp has not been warmed up and is low in electric resistance when the lamp is turned on, a current which is several times the rated current for the lamp flows through the circuit of the lamp for a moment subsequent to the closing of the circuit, namely, for a period of transient phenomenon following the switching action. Accordingly, a lighting system in FIG. 1 (a) which has been generally used heretofore has a drawback that the contacts and switching elements of the start switch S are liable to be fused or broken even where such constituent elements of the switch are well capable of withstanding the rated current for the exposure lamp L.

In order to eliminate such drawback, a lighting system as shown in FIG. 1 (b) is already known. Although the winding CL included in this system serves to protect the contacts and other switching elements from the transient phenomenon caused by tuming-on of the exposure lamp L, the winding CL must be of a large current capacity and the provision of the winding lowers the electrical efficiency of the exposure lamp while it is on.

Another system is also known wherein as illustrated in FIG. 1 (c) the circuit of exposure lamp L includes a triac T which is triggered into conduction when a start switch S is closed to energize an R-C circuit consisting of a resistor R and a capacitor C. Even with such system, however, the contacts or switching elements can not be free from fusion or damage to be caused by the flow of a large current when the exposure lamp is turned on.

Further the systems of FIGS. 1 (a) and (c) have another drawback that the flow of a large current as a transient phenomenon produced when the exposure lamp is turned on deteriorates the life of the exposure lamp. Another drawback attending the systems of FIGS. 1 (a) and (c) is that they fail to achieve satisfactory buildup of illumination when the exposure lamp is turned on. Put another way, the exposure lamp takes a long time to produce a predetermined intensity of illumination, so that it is impossible to make exposures within a short period of time.

SUMMARY OF THE INVENTION An object of the present invention is to control a transient phenomenon which occurs when the exposure lamp is turned on and to thereby completely eliminate fusion, damage or like troubles to be caused to the contacts of a start switch and the like.

Another object of the present invention is to provide a system which permits the exposure lamp to achieve excellent buildup with improved electrical efficiency when it is turned on so as to enable copying apparatus to effect a short period of exposures with high efficiency and safety.

Still another object of the present invention is to provide a system which is capable of providing with extreme ease illumination of a desired intensity for exposure in accordance with the kind and distinctness of original documents.

In order to fulfil the foregoing objects, the present invention is characterized by a structure comprising a triac inserted in the electric circuit of an exposure lamp in series therewith and a trigger circuit for triggering the triac into a conducting state at a small conduction angle simultaneously when a main switch is turned on and triggering the triac into a conducting state at a large conduction angle simultaneously when a start switch is turned on, the start switch being controlled for on-off operation by initiation of copying operation in response to the movement of an original document or photosensitive paper. The trigger circuit comprises a first trigger circuit for triggering the triac into a conducting state at a small conduction angle simultaneously when the main switch is turned on and a second trigger circuit for triggering the triac into a conducting state at a large conduction angle simultaneously when the start switch is turned on. Alternatively, the trigger circuit may comprise a circuit which provides the same action to the triac as the combination of the first and second trigger circuits.

When the main switch is turned on in the foregoing system, the triac is allowed to function at a small conduction angle to preliminarily light the exposure lamp to such an extent as will not be detrimental to copying operation. When an original document is then placed in position and the start switch is turned on in response to the movement of the document or photosensitive paper, the triac is caused to operate at a large conduction angle to bring the exposure lamp into full illumination to give a desired exposure to the photosensitive paper. The start switch may preferably be a timing switch which automatically opens its circuit upon lapse of a predetermined period of time or a switch having an identical function. When the switch is turned off, the exposure lamp is brought back to the same state as in the preliminary stage of illumination.

Since the exposure lamp is pre-lighted upon turning on of the main switch and is then brought into full illumination by the start switch, the flow of an excess rush current into the circuit for heating the filament of the lamp is eliminated when the exposure lamp is initiated into full illumination as well as when it is pre-lighted, with the result that the contacts, switching elements and the like of the main switch and start switch can be completely protected from excess current, the hazard of fusion or breakage thus being avoided. In addition, the preliminary lighting of the exposure lamp effected by the main switch permits the exposure lamp to build up its brightness satisfactorily when it is initiated into full illumination, allowing the electric circuit to achieve improved electrical efficiency. Thus, the copying apparatus can provide exposures within a short period with the highest efficiency and safety.

Further in accordance with the present invention, the trigger circuit for switching the exposure lamp into full illumination may include control means such as a variable resistor for adjusting the brightness of the exposure lamp as desired, whereby the intensity of illumination produced by the lamp can be varied in accordance with the kind or distinctness of the original document.

Other objects and features of the present invention will become more apparent from the detailed description of the embodiments of this invention given below.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), (b) and show various electric circuits for lighting exposure lamp heretofore known;

FIG. 2 is an electric circuit diagram of an embodiment of the present invention;

FIGS. 3 and 4 are electric circuit diagrams of other embodiments of the present invention;

FIGS. 5 (a), (b) and (c) are diagrams of waveshapes of a voltage to be applied to the exposure lamp in the embodiment of FIG. 2, FIGS. 5 (a) and (b) showing the state when the start switch is off, FIG. 5 (0) showing the state when the start switch is on; and

FIGS. 6 (a) and (b) are diagrams of waveshapes of a voltage to be applied to the exposure lamp in the embodiment of FIG. 3, FIG. 6 (a) showing the state when the start switch is off, FIG. 6 (b) showing the state when the start switch is on.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 2, the electric circuit of an exposure lamp 2 to be opened or closed by a main switch 1 includes a triac (triode ac switch) 3 inserted in series therewith. The triac 3 which functions at desired two different conduction angles, namely at large and small angles, when triggered by a trigger circuit 4,applies AC voltage to the exposure lamp 2.

The trigger circuit 4 comprises a first trigger circuit 5 for switching the triac 3 into conduction at a small conduction angle and a second trigger circuit 6 for firing the triac into conduction at a large induction angle. The first trigger circuit 5 including a diode 7, a variable resistor 8 and a capacitor 9 functions simultaneously when the main switch 1 is closed and, in accordance with the time constant determined by the variable resistor 8 and capacitor 9, triggers the gate of the triac 3 through a diac (diode ac switch) or a bidirectional diode thyristor (semiconductor symmetrical switch) 10 to operate the triac 3 at a small conduction angle, The voltage to be applied to the exposure lamp 2 at this time has a waveshape of FIG. 5 (b) having a low effective voltage as obtained by half-wave rectification with the diode 7 and controlling the variable resistor 8 so as to adjust the conduction angle of the triac 3, for example, to the form of FIG. 5 (a) as represented by the hatched portion between 1r/2 and 1r of the half cycle of the AC voltage. Thus the exposure lamp 2 is brought to a preliminary state of illumination. Such pre-lighted state of the exposure lamp 2 is brought about simultaneously with closing of the main switch 1, prior to the initiation of copying operation and the effective voltage for this purpose may preferably be set at the highest possible level which will not produce any adverse effect on copying operation, in preparation for the subsequent full illumination of the exposure lamp 2 to be described later. The voltage can be determined as desired by controlling the variable resistor 8. Further the voltage across the first trigger circuit 5 is maintained at a constant level by a neon glow lamp 11 which is disposed in parallel with the diode 7, variable resistor 8 and capacitor 9 and which absorbs variation in the conduction angle of triac 3 when the power source voltage becomes higher.

The second trigger circuit 6 including a resistor 12 and a capacitor 13 is opened or closed by a start switch 14 and accordingly the second trigger circuit 6 is not energized by closing of the main switch 1.

The start switch 14 is operatively related with the insertion of an original document or feeding of photosensitive paper. Employed for this purpose is a timing switch which is closed when pushed by the leader end of the original document or photosensitive paper or when a start switch button on an operation panel of the copying apparatus is depressed, the timing switch further being such that it is opened upon lapse of a given period of time.

When the start switch 14 is closed by insertion of the original document or forward movement of photosensitive paper, the triac 3 is brought to a conducting state in accordance with the time constant determined by the resistor 12 and capacitor 13 in the second trigger circuit 6. Such conduction takes place at a great conduction angle determined by a set value of the resistor 12, so that a high effective voltage as represented by the hatched portion of FIG. 5 (c) is applied to the exposure lamp 2 for full illumination, as distinct from the above-mentioned pre-lighted state. Thus, an effective voltage corresponding, for example, to about to 98% of the power source voltage as seen in FIG. 5 (c) is applied to the exposure lamp 2.

Since the exposure lamp 2 is preliminarily turned on as already described prior to full illumination for copying operation, initiation into full illumination does not cause a flow of a large rush current due to a transient phenomenon. Further because the effective voltage for pre-lighting is low as illustrated in FIGS. 5 (a) and (b), the rush current involved in pre-lighting is also small, with the result that the contacts and switching elements of the start switch can be prefectly protected. Further the control of the variable resistor 8 of the first trigger circuit 5 serves to correct the variations of the effective I voltage for the preliminary lighting. In the case where a variable resistor is used as the resistor 12 of the second trigger circuit or another variable resistor is employed in combination with the resistor 12, the intensity of illumination to be produced by the exposure lamp 2 during full operation can be adjusted by controlling the variable resistor, making it possible to control the amount of exposure for the photosensitive paper in accordance with the kind or distinctness of the original document.

Since the exposure lampv 2 is initiated into full by utilizing the vertical portion of the waveshape of the voltage as illustrated in FIG. 5 (c), the illumination can be built up very satisfactorily. In place of the second trigger circuit 6, it is also possible to provide a circuit including a start switch 15 as indicated in the dotted line in FIG. 2 so as to short-circuit the triac 3 simultaneously with closing of the start switch 15, the circuit thus substituting for the maximum conduction angle of the triac 3.

FIG. 3 shows an embodiment wherein the diode 7 in the first trigger circuit 5 in the embodiment of FIG. 2 is eliminated. More specifically, a first trigger circuit 25 in the embodiment in FIG. 3 comprises a variable resistor 28 and a capacitor 29, and a triac 23 is triggered through a resistor 36 and diac 30 upon closing of the main switch 21 in accordance with the time constant determined by the variable resistor 28 and the capacitor 29, the triac thus being brought into conduction at a small conduction angle to pre-light the exposure lamp 22. Since the first trigger circuit 25 includes no diode,

the voltage applied to the lamp 2 is in the form of full wave as shown in FIG. 6 (a) which is obtained by way of the triac 23 which is in a conducting state at a small conduction angle corresponding to the controlled value of the variable resistor 28, the effective voltage being low as indicated at the hatched portion in the figure. As in the case of FIG. 2, therefore, the exposure lamp 22 is pre-lighted with a substantially low effective voltage.

Just as in FIG. 2, a second trigger circuit 26 includes a resistor 32 and a capacitor 33 and the circuit is opened or closed by the start switch 34. Closing of a start switch 34 brings the triac 23 into a conducting state at a large conduction angle by way of diac 30 in accordance with the time constant determined by the resistor 32 and capacitor 33 as in the embodiment of FIG. 2, so that an AC current having a high effective voltage as illustrated in FIG. 6 (b) is supplied to the exposure lamp 22 to bring it into full illumination. Thus exactly the same result as in the case of FIG. 2 will be obtained. Further a circuit including a start switch 35 as shown in dotted line in the drawing may of course be substituted for the second trigger circuit 26 to shortcircuit the triac 23, the arrangement being such that simultaneously with closing of the start switch 35 the whole power source voltage is applied to the exposure lamp 22 to light the lamp 22 to full extent.

In both embodiments shown in FIGS. 2 and 3, the start switches 14 and 34 or and 35 are opened upon lapse of a definite period of time to de-energize the second trigger circuit, and the triac is triggered by the first trigger circuit into a conducting state at a small conduction angle to thereby bring the exposure lamp to the pre-lighted state.

The embodiment shown in FIG. 4 includes an oscillator 57 inserted into a trigger circuit 44 for the gate of a triac 43.

The oscillator 57 is provided with a circuit 45 corresponding to the first trigger circuit already described and a circuit 46 corresponding to the second trigger circuit, the circuits being connected to a terminal (a) and a terminal (b) respectively, a start switch 54 being provided which serves as a change-over switch for normally closing the terminal (a). The oscillator 57 is actuated upon closing a main switch 41 to trigger the gate of the triac 43 through the terminal (a), start switch 54 and a pulse transformer 58 so as to bring the triac 43 into conduction at a small conduction angle and thereby pre-light the exposure lamp 42.

When the start switch 54 is actuated upon initiation of copying operation to open the terminal (a) and close the terminal (1;) of the oscillator 57, the triac 43 is triggered into conduction at a large conduction angle to light the exposure lamp 42 to full extent. In place of the start switch 54, a circuit for short-circuiting the triac 43 including a start switch 55 may alternatively be provided to pre-light the exposure lamp 42 by closing the start switch 55. In this case, the terminal (a) of the oscillator 57 is connected to the pulse transformer 58 with the terminal (b) left as it is as a free terminal.

In each of the foregoing embodiments, a silicon controlled rectifier may of course be substituted for the triac.

I claim:

1. A lighting system in a copying apparatus including a main switch for actuating said apparatus, means including a start switch responsive to the advance of a sheet for initiating a copying cycle, a light source, and means including a triac in series with said light source for connecting said light source to a source of current and having a triggering electrode, further comprising a first trigger circuit means responsive to the actuation of said main switch for applying a preset constant small conduction angle signal to said triac trigger electrode concurrently with the actuation of said main switch to partially energize said light source, and second trigger circuit means responsive to the actuation of said start switch for applying a preset constant large conduction angle signal to said triac trigger electrode to increase the current through said light source to full illumination energization, following the triggering by said first trigger circuit means.

2. The lighting system as set forth in claim 1 wherein said trigger circuit means includes an oscillator provided with a terminal for triggering said triac into a conducting state at a small conduction angle simultaneously when said main switch is turned on and another terminal to be incorporated into said circuit by the operation of said start switch so as to trigger said triac into a conducting state at a large conduction angle.

3. The lighting system of claim 1 wherein said first trigger circuit means includes a diac, a resistor and a capacitor and triggers said triac through said diac which is connected in series between said resistor and capacitor into a conduction state at a small conduction angle in accordance with a time constant which is a function of said resistor and capacitor upon the closing of said main switch.

4. The lighting system of claim 1 comprising means including a variable resistor for adjusting said small conduction angle signal.

5. The lighting system of claim 1 wherein said first trigger circuit means for maintaining the conduction angle of said triac is independent of voltage changes in said current source.