Exposure amount adjusting device

An exposure amount adjusting device comprises a stepping motor which serves as a drive source and includes a rotor, a stator and an exciting coil; and an exposure amount adjusting arrangement which is driven by the stepping motor. The exposure amount adjusting arrangement includes a fixed member having an aperture to give a passage to light, a positioning member and a bearing which are arranged away from the aperture, the positioning member determining the position of the stator, the bearing rotatably carrying the stator; a rotary member which has another light passing aperture and is arranged to be driven by the rotor; and light shielding blades which are swingably carried by both the fixed and rotary members and arranged to vary their aperture shielding areas according to a rotating position of the rotary member.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an exposure amount adjusting device such as a 
shutter or a diaphragm device to be used for a still camera, a video 
camera or an interchangeable lens for a camera. 
2. Description of the Related Art 
An exposure amount adjusting device has been disclosed in U.S. patent 
applications, Ser. No. 035,453 (filed Apr. 7, 1987) and Ser. No. 122,764 
(filed Nov. 19, 1987) both of which were assigned to the assignees of the 
present application. The exposure amount adjusting device is arranged to 
open and close light shielding blades with a stepping motor which serves 
as a drive source by rotating a rotor while having a stator in a 
stationary state. The stepping motor is disposed away from the position of 
a passage provided for a light beam. 
An exposure amount adjusting device of this kind comprises a diaphragm part 
and a driving part. The diaphragm part includes a cam, diaphragm blades 
for light shielding, a rotary ring, a rotary ring retaining plate, screws, 
etc. The driving part includes a stator, a stator guide, an exciting coil, 
a magnetic rotor, a rotor gear, a base plate, a driving base plate, 
screws, etc. 
However, these numerous components of the diaphragm part and the driving 
part necessitate complex assembly work which is to be performed for 
mounting, connecting and screwing from many directions. This has caused an 
increase in the number of assembly and adjustment processes and thus 
resulted in an increase in cost. Further, the conventional exposure amount 
adjusting device has been arranged to have one of the bearings of the 
rotor of the stepping motor disposed on the driving base plate and to have 
the driving base plate coupled to a cam with screws. The driving base 
plate has been thus arranged to serve as one of the bearings of the 
stepping motor. This further increases the number of components. Besides, 
the arrangement to couple the driving base plate to the cam makes it 
necessary to accurately adjust a distance between the axes of the driving 
gears. That arrangement further increases the number of processes for 
assembly and adjustment work and thus has further increased the cost of 
the device. 
Further, in the conventional exposure amount adjusting device of this kind, 
the rotor of the stepping motor has been prepared as follows: A stainless 
shaft of it is insert-molded in a plastic magnet and, after magnetization, 
a pinion gear is pressure-fitted on the shaft while carrying out 
positioning work. However, this also has caused a further increase in the 
number of assembly processes as well as in the number of component parts. 
A further drawback of the conventional device has resided in difficulty in 
the position adjustment of the magnetic pole of the rotor to the pinion 
gear. Because of this difficulty, the pinion gear is positioned by 
pressure fitting at random relative to the magnetic pole of the rotor. 
This has necessitated accurate adjustment of the aperture of the diaphragm 
and thus caused a further increase in cost. 
Further, in the conventional exposure amount adjusting device, the stator 
of the stepping motor and an iron core which serves as the magnetic path 
thereof are made of discrete members. Hence, it has been necessary to 
couple the iron core to the stator by means of a screw, which also has 
caused an increase in the number of parts, complexity of assembly work and 
a still further increase in cost. 
The conventional exposure amount adjusting device is provided with an 
opening switch for detecting the open position of the diaphragm blades. 
This switch is mounted on a base, which is secured to the retainer plate 
of the rotary ring by heat caulking. However, since the base is secured by 
heat caulking with a supersonic wave or the like, the base tends to have a 
rattling play. The play then necessitates readjustment to prevent unstable 
switching position of the switch. This also has increased the number of 
parts and the cost of the device. 
Further, there ha been provided no special means for facilitating the 
assembly work on the cam, the rotary ring and the diaphragm blades. 
Therefore, in mounting the rotary ring after the diaphragm blades has been 
mounted on the cam, the blades tend to move to make the rotary ring 
mounting work difficult. 
Further, in cases where the exposure amount adjusting device of this kind 
is arranged to have the cam and the rotary ring coupled with each other by 
a bayonet method in a manner, for example, as disclosed in U.S. Pat. No. 
4,152,064, a stopper is discretely arranged to prevent excessive rotation 
of the rotary ring. In this case, however, since the stopper is a discrete 
member, it not only increases the number of parts but also necessitates 
additional work such as screwing, positioning, etc. and thus also has 
resulted in a further increase in cost. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an exposure amount adjusting 
device which is arranged to permit reduction in the number of component 
parts and in the number of processes of assembly work. 
Other objects and features of the invention will be apparent from the 
following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is an exploded oblique view showing an embodiment of this invention. 
The illustration includes a rotary cam 1; an opening switch 2; diaphragm 
blades 3 arranged to block light; a rotary ring 4; a stator 5; an exciting 
coil 6; a stator 7; a rotor 8; a stator 9; an exciting coil 10; a stator 
11; and a base plate 12. 
The rotary cam 1 has cam grooves 1A which are provided in the same number 
as the diaphragm blades 3 for positioning control over the blades 3. The 
cam 1 also has at least three claw parts 1B which are arranged along the 
periphery of the cam 1 to form a bayonet mechanism in conjunction with the 
rotary ring 4. A bearing 1C is arranged to rotatably carry the rotor 8 and 
is in the form of a shaft hole. Studs 1D are provided for mounting the 
stators 5 and 7 and the exciting coil 6. Studs 1E are likewise provided 
for mounting the stators 9 and 11 and the exciting coil 10. In other 
words, the studs 1D and 1E are provided for positioning. Through holes 1H 
are arranged to be used for positioning during assembly work. An aperture 
1I is arranged to provide passage therethrough for a light beam. 
In the case of this embodiment, the exposure amount adjusting device is 
provided with five diaphragm blades 3. Dowels 3B are connected with the 
hole 4E of the rotary ring 4 and are arranged to enable the blades 3 to 
move accordingly as the rotary ring 4 rotates. When the blades 3 move, 
another set of dowels 3A which are disposed on one side of the blades 3 
opposite to another side having the dowels 3B, as shown in FIG. 5, move 
within the cam groves 1A of the cam 1. The diaphragm blades 3 thus act to 
open and close the diaphragm aperture which are encompassed by the blades 
3. 
The rotary ring 4 is provided with notches 4A which are arranged to form a 
bayonet mechanism in conjunction with the claw parts 1B of the cam 1 and 
are in a position corresponding to the claw parts 1B; and an aperture 4F 
which is arranged to provide a passage for a light beam. A lever 4B is 
arranged on the rotary ring 4 to drive the opening switch 2 which is 
provided for detecting the diaphragm aperture opening state of the 
diaphragm blades 3. When the diaphragm blades 3 are in an open state, the 
opening switch lever 4B pushes the opening switch 2 to detach it from an 
opening switch dowel 13 of the stator 5 to bring the opening switch 2 into 
a nonconductive state. When the rotary ring 4 turns round to stop down the 
aperture defining position of the diaphragm blades 3, the opening switch 2 
and the opening switch dowel 13 become conductive. 
The opening switch 2 is arranged to detect the open state of the blades 3 
to produce an electrical signal. The switch 2 operates under the control 
of an open loop because a stepping motor is used as a drive source. The 
switch 2 prevents occurrence of any trouble when the diaphragm blades 3 
fail to operate due to some reason and permits prompt confirmation of the 
condition of the blades 3 when the power supply of the system using this 
device is switched on. 
FIG. 2 shows the opening switch 2 as in an assembled state. Referring to 
FIG. 2, a shaft 1F is arranged to carry the coil part of the opening 
switch 2. A whirl-stop member 1G is arranged to prevent the opening switch 
2 from turning round. The shaft 1F and the whirl-stop member 1G are formed 
in one body with the cam 1, so that positional accuracy can be enhanced. 
The opening switch dowel 13 is secured to the stator 5 and is in an 
electrically conductive state. A flexible circuit board 14 is provided for 
supplying the signal of the opening switch 2 to the driving circuit and is 
soldered to the end part of the switch 2 and the stator 5. 
The above stated opening switch lever 4B is arranged to prevent the rotary 
ring 4 from coming off from the cam 1 as another function thereof, 
because: Since the rotary ring 4 and the cam 1 are bayonet coupled 
together, the rotary ring 4 would be detached from the cam 1 if it turns 
round more than a given degree. With the stator 5 mounted, the end face 5C 
of the stator 5 serves to stop the opening switch lever 4B from moving to 
maintain the bayonet coupling. The rotary ring 4 has a whirl-stop dowel 
4C, which is also arranged to prevent the bayonet disengagement in 
conjunction with the end face 9C of the stator 9. In other words, the 
rotary ring 4 never detaches from the cam 1 with the stators 5 and 9 
mounted after the rotary ring 4 is mounted. The end faces 5C and 9C of 
these stators 5 and 9 thus serve as rotation limiting members for 
mechanically preventing the excessive rotation of the rotary ring 4. 
The stators 5, 7, 9 and 11 have comb-shaped magnetic pole parts 5A, 7A, 9A 
and 11A which are opposed to the rotor 8 and also have connection parts 
5B, 7B, 9B and 11B which form magnetic paths. The stators 5 and 7 are 
magnetically connected by the connection parts 5B and 7B and thus form a 
phase. Stators 9 and 11 are likewise connected to form one phase. These 
phases have exciting coils 6 and 10 respectively. In other words, a 
two-phase stepping motor is used for the embodiment. FIG. 3 shows the 
details of the connection parts of the stators. FIG. 4 shows them in a 
sectional view. 
The stators 5, 7, 9 and 11 are assembled with their positions determined by 
means of the studs 1D and 1E of the cam 1 respectively. The connection 
parts 5B, 7B, 9B and 11B are obtained by bending parts of the stators 5, 
7, 9 and 11 by press working. It is impossible to tightly connect the two 
connecting parts to each other because: Since the stators 5, 7, 9 and 11 
are positioned by means of the studs 1D and 1E of the cam 1, the 
connection parts cannot be tightly connected to each other by precisely 
carrying out the press working process. In view of this, the dimensions of 
parts are predetermined in such a way as to have a gap between connecting 
parts. This prevents the connecting parts from protruding and hindering 
correct positioning work on the stators by means of studs 1D and 1E. 
However, in respect of the magnetic characteristic, an air gap between the 
stators causes too much reluctance to degrade the characteristic of the 
motor. To solve this problem, therefore, the gap part is filled with a 
magnetic matter 16. The magnetic matter 16 is preferably some soft 
magnetic matter such as iron, ferrite or the like which is in a particle 
or liquid state or may be obtained by mixing some adhesive or the like 
with such soft magnetic matter. 
The rotor 8 is made of a plastic magnet and is formed in one body with a 
shaft 8C and a pinion gear 8B. This not only enables the shaft 8C and the 
magnet 8D to have a high degree of concentricity with each other but also 
a dowel (or recess) 8A to be formed at the end face of the the magnet 8D. 
With this dowel 8A used as reference for magnetization, the position of 
the pinion gear 8B can be accurately obtained in relation to the position 
of the magnetic pole. In assembling the rotor 8 with the stators, the 
angular position of the rotary ring 4 can be determined by setting the 
dowel 8A in a predetermined position. Then, a necessary degree of 
precision is attainable without making fine adjustment of the open 
position of the diaphragm blades. 
The exciting coils 6 and 10 are respectively interposed in between the 
stators 5 and 7 and between the stators 9 and 11. The winding ends of the 
coils 6 and 10 are allowed to pass through the holes provided in the 
stators 7 and 11 and to be connected either to a printed circuit board or 
a flexible circuit board which is not shown on the upper surface of the 
base plate 12. Further, as shown in FIG. 1, the base plate 12 has a 
bearing 12A, which rotatably carries the rotor 8. The base plate 12 is 
positioned by means of the studs 1D and 1E of the cam 1. 
With the electro-magnetic exposure amount adjusting device arranged to have 
the stepping motor and the diaphragm device combined in one unit as shown 
in FIG. 1, when a current flows to the exciting coils 6 and 10, a 
repulsing and attracting forces are generated at the magnetic pole parts 
5A, 7A, 9A and 11A. This causes the rotor 8 to rotate on the shaft. Like 
in the case of an ordinary known stepping motor, the rotating degree of 
the rotor 8 is determined by the switching on and off of the power supply. 
The power supply to the rotor 8 begins after confirmation of the state of 
the opening switch 2. 
In the initial stage of the driving action on the diaphragm, the opening 
switch 2 turns on to supply a low level signal to the detecting circuit 20 
shown in FIG. 7. If the diaphragm blades 3 are then having the aperture in 
a state of having been stopped down, a current is supplied to the rotor 8 
in the direction of opening the diaphragm blades 3. This action continues 
until the opening switch 2 is turned off with a high level signal supplied 
to the detecting circuit 20. The current is supplied in the direction of 
stopping down the aperture of the diaphragm blades 3 only after the blades 
3 are opened with the opening switch 2 turned off. While the rotor 8 is 
being turned round to a given degree in the direction of stopping down the 
aperture of the diaphragm blades 3, the rotary ring 4 which engages the 
pinion gear 8B via a rack 4D formed in one body therewith turns round 
accordingly. The diaphragm blades 3 are also operated by the dowels 3B 
accordingly as the rotary ring 4 turns round. Meanwhile, the dowels 3A of 
the diaphragm blades 3 act within the cam grooves 1A of the cam 1 to 
control the position of the blades 3. The aperture of the diaphragm is 
thus determined. An exposure is effected when the diaphragm aperture is 
determined. After that, the diaphragm blades 3 are again opened. Then, the 
operation of the embodiment is completed after the open state of the 
blades 3 is confirmed by means of the opening switch 2. 
Procedures for assembly work on the embodiment are as follows: FIG. 5 shows 
a jig 15 to be used in assembling the diaphragm blades 3. The jig 15 is 
provided with a datum plane for receiving the cam 1 and pins 15A having 
their tips formed in a circular conic shape and arranged to be fit into 
the through holes 1H provided in the cam 1. When the cam 1 is set on the 
jig 15, the pins 15A which have the circular conic tips enter the through 
holes 1H. Then, the circular conic recesses 3A-1 (see FIG. 6) of the 
dowels 3A are adjusted to the circular conic pins 15A of the jig 15. By 
this, one positioning point is determined for the diaphragm blades 3. The 
diaphragm blades 3 are then moved to adjust the position of the dowels 3B 
to the holes 4E of the rotary ring 4 by using this point as a fulcrum. The 
rotary ring 4 is mounted after the diaphragm blades 3 are positioned. The 
claw parts 1B of the cam 1 then come to the position of the notches 4A of 
the rotary ring 4. After that, the cam 1 and the rotary ring 4 are removed 
together from the jig 15, and the rotary ring 4 is turned round. Then, the 
position of the notches 4A of the rotary ring 4 deviates from the claw 
parts 1B of the cam 1 to make the rotary ring 4 inseparable from the cam 
1. Following that, the stators 5 and 9 are adjusted to the studs 1D and 1E 
and set in position. With the stators 5 and 9 positioned, the bayonet 
mechanism of the rotary ring 4 and the cam 1 becomes inseparable by virtue 
of the opening switch lever 4B and the whirl-stop dowel 4C. 
The opening switch 2 is mounted on the cam 1 in this manner. The cam 1 has 
a shaft 1F and a whirl-stop member 1G formed in one body for the opening 
switch 2. After the opening switch 2 is mounted, the rotary ring 4 is 
turned round to bring the diaphragm blades 3 into an open state. Then the 
rotor 8 is positioned by setting the dowel 8A in position. The rack 4D of 
the rotary ring 4 is then engaged with the pinion gear 8B of the rotor 8. 
Meanwhile, the stators 7 and 11 are secured to the base plate 12, and the 
exciting coils 6 and 10 are fitted to the connection parts 7B and 11B, 
respectively, beforehand as a sub-unit. This sub-unit is set in its 
assembly position after the rotor 8. At that time, if air gaps left 
between the connection parts 5B and 7B and between the connection parts 9B 
and 11B present a problem in terms of the characteristic of the motor as 
mentioned in the foregoing, these gaps are filled with the magnetic matter 
16. In that instance, that magnetic matter 16 is applied to the connection 
parts 5B and 9B before the sub-unit is mounted. 
In the last place, the tips of the studs 1D and 1E which protrude out of 
the base plate 12 is secured to the plate 12 by heat welding or the like. 
After that, the ends of the exciting coils 6 and 10, the opening switch 2 
and the stator 5 are connected to the driving circuit by means of lead 
wires, a printed circuit board or a flexible circuit board, etc. The 
assembling procedures can be carried out in given sequence without 
necessitating any adjustment work. 
As described above, a feature of this embodiment lies in that: The 
provision of a plurality of positioning studs which serve as reference for 
mounting the driving part on the cam having cam grooves dispenses with a 
stator guide which has been used by the conventional device for 
positioning the stator. Further, a driving base plate and screws which 
have been used by the conventional device for coupling the diaphragm part 
with the driving part also become unnecessary. The embodiment thus permits 
much reduction in the number of required parts. In addition to this, with 
the studs which are erected on the cam serving as assembling reference, 
the stators can be more accurately positioned; the assembly work can be 
simplified as the parts can be assembled only from one direction; the 
connection parts can be lessened; and, therefore, the number of assembly 
processes can be lessened to a great degree. The reduction in the number 
of parts and the number of assembly processes results in reduction in 
weight and in cost. 
Further, the bearing hole which is provided in the cam serves as the 
bearing on one side of the rotor of the stepping motor. The bearing hole 
obviates the necessity of a driving base plate and its mounting screws 
which have been used by the conventional device. This permits reduction in 
the number of parts and weight of the device. Further, the distance 
between the axis of the driving gears is arranged to be determined by the 
positional precision of the bearing hole. The arrangement obviates the 
necessity of adjustment. This also lessens the possibility of such 
inadequate engagement that results from the fluctuating position of 
driving gears obtained when the driving base plate is connected according 
to the conventional arrangement. Besides, since the cam is provided with 
the member for positioning the stators of the stepping motor, the stators 
can be also accurately positioned. 
The arrangement of the embodiment described thus permits reduction in cost 
because of the reduction in the number of assembly processes and that of 
adjustment. 
Further, in the case of this embodiment, the rotor of the stepping motor, 
its shaft and the pinion gear are formed in one body with a plastic magnet 
material. This also permits reduction in the number of parts and in the 
number of assembly processes for cost reduction. Further, the arrangement 
to have the rotor formed in one body with the pinion gear precludes the 
possibility of detachment of the gear and also enhances the precision in 
terms of the concentricity of the shaft and the rotor, so that the 
embodiment has an increased degree of reliability. Further, since the pole 
of the rotor can be adjusted to a part of the gear. The start position of 
the diaphragm blades can be made unvarying by setting this part in a given 
position relative to the gear part of the rotary ring. Therefore, this 
obviates the necessity of fine adjustment work on the aperture and thus 
permits further reduction in cost. The assembly work is further simplified 
by the provision of an assembly mark which is provided at a peripheral 
point of the rotor for facilitating the assembly work. 
Further, a part of each stator of the stepping motor is bent and used as an 
iron core. This arrangement obviates the necessity of using some 
additional member as an iron core, so that the number f parts and that of 
assembly processes can be further reduced. Further, this not only enables 
the assembly work to be performed only in one direction to permit 
automatic assembly work but also enhances the efficiency of the stepping 
motor. The above stated arrangement to fill the air gap between the upper 
and lower stators with a soft magnetic matter such as Fe.sub.3 O.sub.4 or 
the like prevents an increase in the reluctance of the magnetic circuit of 
the stator. 
Further, in the embodiment described, the shaft which is provided for 
mounting the opening switch and the whirl-stop member are formed in one 
body at a part of the cam. This arrangement not only permits reduction in 
the number of parts but also dispenses with a heat caulking process which 
has been necessary for the conventional device. The dowel which serves as 
an electrode for the opening switch is formed at a part of the stator of 
the stepping motor. It obviates the necessity of an addition part to 
permit cost reduction. Further, unlike the conventional device, the 
embodiment is free from the fear of unstableness of switch positions due 
to a play at a switch base discretely mounted. This ensures stabilization 
and enhances the quality of the embodiment. 
In the embodiment described, a through hole is provided in a part of each 
cam groove of the cam plate while a circular conic recess is provided in 
each dowel of the diaphragm blades on one side thereof facing the cam 
plate. This arrangement permits the use of the jig, which enables the 
rotary ring to be promptly assembled without difficulty. 
Further, in the embodiment, a part of the stator of the stepping motor 
which is assembled with highly accurate positioning is used as a rotation 
limiting member for the rotary ring. This member serves also as a 
mechanical stopper for the maximum or minimum aperture position of the 
diaphragm. This member thus also permits reduction in the number of parts; 
obviates the necessity of adjustment work on the stopper position for the 
maximum or minimum aperture. Therefore, the number of assembly processes 
can be reduced to lower the cost of the device.