Variable illuminating angle mechanism for a flash unit

A variable illuminating angle mechanism which can vary the illuminating angle of a flash unit. The variable illuminating angle mechanism includes a device which prevents a light emitting body or an illuminating lens from being moved in excess of a range of normal movement. The variable illuminating angle mechanism includes a drive shaft having a screw thread formed on a circumferential surface of the drive shaft and a drive device to rotationally drive the drive shaft. A transmission member in threaded connection to the drive shaft is moved by rotation of the drive shaft, and a transmission device moves the light emitting unit or the illuminating lens via movement of the transmission member. An escape device is positioned at at least one end of the drive shaft to disconnect the transmission member from the drive shaft when the transmission member is moved beyond a normal operating range of the light emitting unit or illuminating lens. When the escape device disconnects the drive shaft from the transmission member, the drive shaft rotates without driving the transmission member to prevent the variable illuminating angle mechanism from locking and causing damage to the variable illuminating angle mechanism components.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a flash unit having a variable 
illuminating angle mechanism which changes the illuminating angle of a 
flash unit, and, more particularly, the present invention relates to a 
variable illuminating angle mechanism for a flash unit which stops the 
movement of a light emitting body or an illuminating lens within the flash 
unit from exceeding a normal operating range. 
2. Description of the Related Art 
When flash photography is performed with a camera, it is necessary for the 
field angle of the photographic lens and the illuminating angle of the 
flash unit to overlap. In a conventional camera, to control the overlap of 
the field angle and the illuminating angle, the camera transmits data 
representing the focal length of the photographic lens to the flash unit, 
and the flash unit uses the focal length data to adjust the illuminating 
angle by causing a light emitting body or an illuminating lens to move. 
This type of camera is disclosed in Japanese Laid-Open Patent Publication 
No. JP-A-2-207139, and in Japanese Laid-Open Patent Publication No. 
JP-A-57-120922. 
FIG. 7 is a cross-sectional diagram of a conventional flash unit 71 of the 
type described above. As shown in FIG. 7, the flash unit 71 includes a 
motor 73 which rotationally drives a freely rotatable drive shaft 72. A 
transmission member 74 is in threaded connection to the drive shaft 72, 
and is also connected to a light emitting body 75. As the motor 73 
rotationally drives the drive shaft 72, the transmission member 74 is 
moved which in turn moves the light emitting body 75. Further, an 
illuminating window 76 consisting of a Fresnel lens is positioned in the 
illuminating direction of the light emitting body 75. 
A contact 77 is fixed to the lower surface of the transmission member 74, 
and a contact point 78 located along the drive shaft 72 makes sliding 
contact with the contact 77. The contact point 78 is connected to a 
control unit 79, and an output of the control unit 79 is connected to the 
motor 73. An input terminal of the control unit 79 is connected to 
components in the camera. 
In operation of the flash unit shown in FIG. 7, the control unit 79 
calculates a target position of the light emitting body 75 according to 
focal length information provided from the camera to provide an 
appropriate illumination angle. Next, the control unit 79 measures the 
actual position of the light emitting body 75 according to the state of 
the contact point 78, and the control unit 79 provides a drive output to 
the motor 73 corresponding to the positional deviation of the target 
position and the actual position. The motor 73 then rotationally drives 
the drive shaft 72 according to the output from the control unit 79. The 
control unit 79 successively detects the position of the transmission 
member 74 as the light emitting body 75 is driven to the target position, 
and stops the motor 73 after it has driven the transmission member 74 and 
the light emitting body 75 to the target position. In the above-described 
manner, the illuminating angle of the flash unit 71 is adjusted by 
changing the position of the light emitting body 75 within the flash unit 
71. 
When, for example, a zoom lens is used, the focal length of the 
photographic lens frequently changes according to the photographic 
circumstances. Because of the frequent changes of the focal length when 
using a zoom lens, a mechanism as shown in FIG. 7 which adapts the 
illuminating angle to the focal length is advantageous to increase the 
mobility of photography. 
However, when an input of data representing the position of the 
transmission member 74 is absent due to electrical open circuit or poor 
connection, the control unit 79 becomes unable to detect the position of 
the light emitting body 75. In such a state, the control unit 79 drives 
the motor 73 continuously. Further, because the flash unit 71 impresses a 
high voltage trigger on the light emitting body 75 at this instant, 
electrical noise acts on the control unit 79. Since the control unit 79 
consists of a microcomputer or the like, the electrical noise causes 
operations other than the programmed operations to arise (hereinafter 
referred to as "runaway"), and there is a risk of the motor 73 continuing 
to rotate. 
In the case that the control unit 79 is unable to detect position data of 
the transmission member 74, it is possible to stop the motor 73 if the 
motor 73 is caused to rotate for more than a predetermined time. Such a 
system is disclosed in Japanese Examined Patent Publication JP-B-7-27150. 
However, in the case that runaway of the control unit 79 occurs, a stop 
command by the control unit 79 is not generated, and no stop operation is 
performed. If no stop operation is performed, the motor 73 continues to 
rotate, and there is a risk of failure of the variable illuminating angle 
mechanism. Moreover, when the transmission member 74 reaches the end of 
the drive shaft 72, and the rotation of the motor 73 is forced to stop 
(hereinafter referred to as "lock"), a risk of failure of the motor 73 
arises. 
Generally, as a countermeasure against the kinds of problems described 
above, a slipping clutch is disposed between the motor 73 and the drive 
shaft 72 so that the motor 73 does not lock. However, when a slipping 
clutch is used between the motor 73 and the drive shaft 72, it is 
necessary to provide a sliding surface with a predetermined static 
frictional force in order to transmit the drive force to the drive shaft 
72 during normal operation. A problem occurs in that a comparatively large 
sliding frictional force occurs during an abnormality, causing the sliding 
surface to wear and its durability to become low. 
Furthermore, a problem occurs in that the large sliding frictional force 
acts on both the motor 73 and the drive shaft 72, becoming a new origin of 
failure in the variable illuminating angle mechanism. 
Moreover, a problem occurs in that the necessity of using a slipping clutch 
between the motor 73 and the drive shaft 72 causes the transmission 
mechanism to become complicated. As a result, the ease of assembly of the 
flash unit becomes poor and the size of the flash unit is increased. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a variable illuminating 
angle mechanism for a flash unit which prevents locking of a drive device 
due to anomalous operation and has a high durability and simple 
construction. 
It is another object of the present invention to provide a variable 
illuminating angle mechanism for a flash unit which can accurately and 
rapidly restore the variable illuminating angle mechanism from a state in 
which locking of the drive device has been prevented to a state in which 
normal operation is possible. 
It is another object of the present invention to provide a variable 
illuminating angle mechanism which quickly reinstates normal operation 
when an anomalous condition occurs. 
It is yet another object of the present invention to provide a variable 
illuminating angle mechanism which can efficiently set a movement range of 
a light emitting body. 
Additional objects and advantages of the invention will be set forth in 
part in the description which follows, and, in part, will be obvious from 
the description, or may be learned by practice of the invention. 
Objects of the present invention are achieved with a variable illuminating 
angle mechanism for a flash unit, the variable illuminating angle 
mechanism including a drive shaft having a screw thread formed on the 
circumferential surface of the drive shaft and a screw escape device 
disposed at at least one end of the drive shaft which slidingly connects 
to the transmission member, a drive mechanism which rotationally drives 
the drive shaft, a transmission member which is in threaded connection to 
the drive shaft and which is moved by rotation of the drive shaft, a light 
emitting unit to illuminate a subject, an illuminating lens and a 
transmission device operatively coupled to the transmission member to 
cause movement of the light emitting body or the illuminating lens via the 
movement of the transmission member. 
The variable illuminating angle mechanism for a flash unit also includes an 
urging device to urge the transmission member toward the center of the 
drive shaft. The urging device includes a flat plate spring member which 
is formed integrally with the transmission member, and a limiting member 
which comes into contact with the spring member when the transmission 
member is moved to the screw escape device. 
The transmission device of the variable illuminating angle mechanism also 
includes a support unit which supports the light emitting unit or the 
illuminating lens, and a cam groove which converts the movement of the 
transmission member into movement of the support unit. At least one end of 
the cam groove may be a linear cam which is formed approximately parallel 
to the movement direction of the transmission member. 
In accordance with embodiments of the present invention, when the drive 
mechanism rotates the drive shaft, the transmission member, which is in 
threaded connection to the drive shaft, moves along the drive shaft. The 
movement of the transmission member is transmitted by the transmission 
device, and converted into movement of the light emitting unit or of the 
illuminating lens. 
When an anomalous operation of the drive mechanism occurs, and the light 
emitting body or the illuminating lens continues to be driven, the 
transmission member moves along the drive shaft as far as a screw escape 
device which is disposed at at least one end of the drive shaft. The screw 
escape device and the transmission member mutually slip, and the 
transmission member does not move further than the screw escape device 
causing the drive shaft to turn without further driving the transmission 
member. Accordingly, because the transmission member does not move further 
when it teaches the screw escape device, the variable illuminating angle 
mechanism is not damaged. Moreover, because the drive shaft slips, the 
lock state of the drive device can be accurately avoided. 
In accordance with embodiments of the present invention, the urging device 
provides an urging force to the transmission member toward the center of 
the drive shaft when the transmission member is moved as far as the screw 
escape device. Since the urging device exerts an urging force on the 
transmission member toward the center of the drive shaft, by reversing the 
rotation of the drive shaft when the transmission member reaches the screw 
escape device, the transmission member can easily be caused to be screw 
connected to the drive shaft. 
By disposing the urging device in this manner, the drive shaft is rotated 
in the reverse direction to eliminate the anomalous drive state, and 
further, the variable illuminating angle mechanism is rapidly returned to 
a normal state in which the illuminating angle can again be varied. 
In accordance with the present invention, the spring member also moves 
accompanying the movement of the transmission member. The spring member 
provides an urging force toward the center of the drive shaft when the 
transmission member is positioned in the screw escape device by contact 
with the outer side of a limiting member. In particular, when the screw 
escape devices are disposed on both sides of the drive shaft, a simple 
construction comprising a single spring member and two limiting members 
positioned on both sides of the single spring member causes the desired 
urging force to act on the transmission member. 
In accordance with embodiments of the present invention, the movement of 
the transmission member is transmitted to the support member via a 
translation cam. By moving the support member which supports the light 
emitting body or the illuminating lens, the illuminating angle of the 
flash unit can be varied. 
However, during normal operation of the variable illuminating angle 
mechanism, the transmission member moves within a range in which a screw 
escape device is not positioned. Once an abnormal state arises, the light 
emitting body or illuminating lens is moved exceeding the normal movement 
range and the transmission member moves to the screw escape device. When 
the normal movement range is exceeded, it is necessary to maintain the 
path of movement of light emitting body or illuminating lens, and the 
flash unit has to be made a large size. 
In accordance with embodiments of the present invention, at least one end 
of the cam shape of the translation cam is formed approximately parallel 
to the movement direction of the transmission member. When the 
transmission member moves a range of the screw escape device, the part of 
the translation cam which is parallel to the movement direction of the 
transmission member limits the amount of movement of the light emitting 
body or illuminating lens because the cam no longer transmits movement to 
the support member. Accordingly, a normal extent of movement path may be 
maintained, without the flash unit being made large.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be made in detail to the preferred embodiments of the 
present invention, examples of which are illustrated in the accompanying 
drawings wherein like reference numerals refer to the same or similar 
elements throughout. 
FIG. 1 is a top view of a variable angle illuminating mechanism suitable 
for a camera flash unit in accordance with embodiments of the present 
invention. FIG. 2 is a front view of the variable angle illuminating 
mechanism for a flash unit in accordance with embodiments of the present 
invention. Embodiments of the present invention will be described first 
with reference to FIGS. 1 and 2. 
As shown in FIGS. 1 and 2, a fixing member 2 (see FIG. 2) located within 
the flash device body 1 fixes a drive mechanism system for the variable 
illuminating angle mechanism. The drive mechanism system includes a motor 
3 located on the rear side of the fixing member 2. The rotation of the 
motor 3 is transmitted via the engagement of gears 3a, 4a to a freely 
rotatable drive shaft 4. The drive shaft 4 includes a screw threaded 
portion 4b cut in its center, and screw escape portions 4c, 4d disposed on 
both sides of the drive shaft 4. The screw escape portions 4c, 4d are 
portions of the drive shaft 4 in which a screw thread is not cut. 
The drive shaft 4 is threaded into a square nut 5, and a left/right slide 
plate 6 is fixed to the square nut 5. The left/right slide plate 6 is 
positioned for free rectilinear motion in a right and left direction 
corresponding to the arrow A in FIG. 1 according to the movement of the 
square nut 5. 
The square nut 5 and the left/right slide plate 6 act as a transmission 
member to transmit the rotation of the drive shaft 4 to a light emitting 
unit 11. A contact 8 (FIG. 1) is fixed to the left/right slide plate 6, 
and a printed plate 9 is fixed in the flash unit body 1 at a position to 
make sliding contact with the contact 8. A common contact point 8a, which 
normally makes contact with one side of the contact 8, and contact points 
8b-8e which make contact with the other side of the contact 8, are located 
on the printed plate 9. The contact 8 and the contact points 8b-8e operate 
as an encoder to detect a position of the left/right slide plate which 
corresponds to an illumination angle position. 
As shown in FIG. 1, a cam groove 6a is formed in the left/right slide plate 
6. A projection 11b, which is fixed to a forward/backward slide plate 11a, 
is inserted and freely slides in the cam groove 6a. The forward/backward 
slide plate 11a slides freely in the forward and backward directions (the 
direction of arrow B in FIG. 1) and acts as a support member to support a 
light emitting unit 11 electrically wired with a xenon tube 12, and the 
like. As the left/right slide plate 6 moves in the left or right 
direction, the sliding movement of the projection 11b in the cam groove 6a 
acts as a transmission device to move the light emitting unit 11 in the 
forward/backward direction. The forward/backward slide plate 11a is 
engaged with a rail 1b which regulates the sliding direction of the light 
emitting unit 11. As shown in FIGS. 1 and 2, the left/right slide plate 6 
is secured to the flash unit body 1 with fixed screws 7 which are screwed 
to screw receiving units 1a of the flash unit body 1. The fixed screws 7 
fit in openings in the left/right slide plate 6 which allow the left/right 
slide plate 6 to move in the left and right directions. The 
forward/backward slide plate 11a is also secured beneath the left/right 
side plate 6 by the screws 7. Moreover, an illuminating lens 13 is 
positioned in an illuminating direction of the light emitting unit 11. 
Further, a flat spring 6c projects from the left/right slide plate 6. The 
flat spring 6c projects between limiting bosses 1d, 1e located on either 
side of the flat spring 6c, which limit movement of the flat spring 6c. 
FIG. 3 is a diagram showing an electrical control system in accordance with 
embodiments of the present invention. As shown in FIG. 3, a camera 51 
having, for example, a zoom lens 52 mounted thereon, transmits data 
representing a focal length of the zoom lens 52 to an interface circuit 54 
of the flash unit via a flash unit mounting contact point 53. The output 
of the interface circuit 54 is input to a control unit 55 which comprises 
a microcomputer, or the like, and associated circuitry. Further, the 
common contact point 8a and the contact points 8b-8e used for illumination 
angle position detection are connected to the control unit 55. The control 
unit 55 includes outputs which are respectively connected to a motor drive 
56 and to a display 57. The output of the motor drive 56 is connected to a 
motor 3 which drives the light emitting unit 11. 
The operation of the embodiments of the invention shown in FIGS. 1-3 will 
now be described below. The motor 3 is rotated in either the forward 
direction or the reverse direction according to the drive output from the 
motor drive 56. The rotation of the motor 3 is transmitted to the drive 
shaft 4 via the gears 3a and 4a. As the drive shaft 4 rotates, the square 
nut 5, which is in threaded engagement with the screw thread 4b, moves in 
the right or left direction in FIGS. 1 and 2 according to the direction of 
rotation of the drive shaft 4. The left/right slide plate 6 moves in the 
right or left direction accompanying the movement of the square nut 5. 
The position of the left/right slide plate 6 is detected by the encoder 
comprising the contact 8 and the contact points 8b-8e, and the detected 
position of the left/right slide plate 6 is input to the control unit 55. 
The control unit 55 determines a control amount which causes the field 
angle of the zoom lens 52 to correspond to the illumination angle of the 
flash device, and outputs the control amount to the motor drive 56. The 
motor drive 56 provides a drive output to the motor 3 which corresponds to 
the control amount determined by the control unit 55. 
Since, as shown in FIG. 1, the cam groove 6a is disposed obliquely in the 
left/right slide plate 6, the movement of the left/right slide plate 6 
causes the forward/backward slide plate 11a and the light emitting unit 11 
to move in the forward/backward direction by movement of the projection 
11b within the cam groove 6b. In the above-described manner, the light 
emitting unit 11 moves forward and backward corresponding to the left and 
right movement, respectively, of the left/right slide plate 6, and the 
illuminating angle of the flash unit is made to vary by changing the 
distance from the light emitting unit 11 to the illuminating lens 13, as 
shown in FIG. 4. 
The square nut 5 moves within a range of normal movement shown as a range C 
in FIGS. 1 and 5. When the movement of the square nut 5 is limited to the 
range C, the flat spring 6c which is integral with and projecting from the 
left/right slide plate 6 does not strike the limiting bosses 1e, 1d formed 
integrally with the flash unit body 1. However, when abnormalities arise 
in the control of the motor 3, the square nut 5 exceeds the normal 
operating range C, and moves into an abnormal operating range C1 or C2, as 
shown in FIG. 5. 
Accordingly, it is necessary to provide a cam groove 6a having ranges D, D1 
and D2 (FIG. 1) in which the projection 11b moves, corresponding to the 
operating ranges C, C1 an C2, respectively, of the square nut 5. Further, 
the forward/backward slide plate 11a moves within ranges F, F1 and F2 
(FIG. 1) corresponding to the operating ranges C, C1 and C2, respectively, 
of the square nut 5. 
When the square nut 5 moves into the abnormal operating range C1, C2, the 
square nut 5 moves outside the screw threaded portion 4b of the drive 
shaft 4, and is positioned in one of the screw escape portions 4c, 4d. The 
square nut 5 slips when it reaches the screw escape portions 4c, 4d 
because no screw thread is cut in the screw escape portions 4c, 4d. 
Because of the slippage of the square nut 5 when the square nut 5 reaches 
the screw escape portions 4c, 4d, the left/right slide plate 6 does not 
move beyond the screw escape portions 4c, 4d, and damage to the variable 
illumination angle mechanism can be prevented. 
Moreover, when the square nut 5 slips when it reaches the screw escape 
portions 4c, 4d, the drive shaft 4 is rotated idly. Accordingly, because 
the drive shaft 4 is rotated idly when the square nut 5 is in the slipped 
state, the motor 3 is prevented from reaching the "lock" state. Thus, the 
screw escape portions 4c, 4d act as escape devices which prevent the 
square nut 5 and left/right drive plate 6 from being driven further when 
an abnormal operating condition occurs, thereby preventing damage to 
various components of the variable illumination angle mechanism. 
Furthermore, when the square nut 5 becomes positioned in the screw escape 
portion 4c (or 4d), the flat spring 6c comes into contact with the 
limiting boss 1e (or 1d). When the flat spring 6c comes into contact with 
the limiting boss 1e (or 1d), the flat spring 6c confers an urging force 
on the left/right slide plate 6 toward the center of the drive shaft 4. 
Accordingly, if the drive shaft 4 is rotated in a direction which is 
reverse to the direction of rotation which caused the square nut 5 to 
reach the screw escape portions 4c, 4d, the thread of the square nut 5 is 
urged by the limiting boss 1e (or 1d) to engage with the screw threaded 
portion 4b, and the square nut 5 can return to the normal operating range 
C. 
A description of the operation of the variable angle illuminating mechanism 
during an example of an abnormal operating condition will now be provided 
below. 
For example, when the focal length of the zoom lens 52 is shortened to 28 
mm, the control unit 55 receives an instruction from the camera 51 for the 
light emitting unit 11 to move to a position corresponding to a 28 mm 
focal length. As the left/right slide plate 6 is moved according to the 
instruction from the control unit 55, the contact 8 slides and short 
circuits the common contact point 8a and the contact point 8b which is at 
a position corresponding to the 28 mm focal length illuminating angle 
position. When poor contact between the contact 8 and any of the contacts 
8a and 8b occurs during control of the movement of the left/right slide 
plate 6, detection of the 28 mm focal length illuminating angle position 
becomes impossible, and the light emitting unit 11 is moved further 
forward. 
As the light emitting unit is moved further forward, the screw engagement 
of the square nut 5 and the screw threaded portion 4b is disconnected when 
the square nut 5 reaches a screw escape portion 4c, 4d. After the screw 
engagement of the square nut 5 and the screw threaded portion 4b is 
disconnected, the motor 3 continues to rotate, but the variable 
illuminating angle mechanism is not moved further because the square nut 5 
slips in the screw escape portion 4c or 4d. Moreover, the control unit 55 
drives the motor 3 for only a predetermined time, and the control unit 55 
can determine the abnormal drive state because the contact 8 does not 
reach the target illuminating angle position corresponding to a 28 mm 
focal length. Further, when the control unit 55 rotationally drives the 
motor 3 in the reverse direction, the square nut 5 easily engages with the 
screw threaded portion 4b due to the urging force of the flat spring 6c. 
When the contact 8 reaches the 35 mm focal length position which is 
adjacent to the 28 mm position, the control unit 55 recognizes this 
position and stops the motor 3 at the 35 mm focal length. The display 57 
then displays an abnormal state with methods such as flashing of the 
display 57 of the illuminating angle. 
Furthermore, if, for any reason, runaway occurs in the microcomputer of the 
control unit 55, and the rotation of the motor 3 can not be stopped, if 
the user notices that the motor 3 is in a state of running idly, the user 
can cut off the power source. When the user does not notice that the motor 
3 is in a state of running idly, the battery of the flash unit becomes 
exhausted, and stops. Accordingly, safety can be maintained in any case. 
Moreover, in accordance with the embodiments of the present invention shown 
in FIGS. 1 and 2, the left/right slide plate 6 is fixed to freely advance 
with the fixed screws 7, and the forward/backward slide plate 11a is 
positioned beneath the left/right slide plate 6. This arrangement of the 
left/right slide plate 6, fixed screws 7 and forward/backward slide plate 
11a prevents the floating up of both the forward/backward slide plate 11a 
and the left/right slide plate 6. 
Furthermore, in accordance with embodiments of the present invention, the 
left/right slide plate 6, cam groove 6a, and flat spring 6c are integrally 
formed. Accordingly, the number of parts required is markedly curtailed, 
and the design can increase the ease of assembly. Moreover, the left/right 
slide plate 6, cam groove 6a and flat spring 6c may be integrally formed 
of inexpensive plastic resins, such as ABS, polycarbonate, polyacetal, 
polypropylene, nylon and the like which have coefficients of friction 
which are comparatively low, and have resilience as a flat spring. The 
design of these components can increase durability. 
FIG. 6 is a diagram showing a modification of the cam groove 6a of the 
left/right slide plate 6 in accordance with embodiments of the present 
invention. The cam groove 6a shown in FIG. 6 includes an oblique surface D 
and two surfaces D1, D2 which are formed in the left/right direction at 
either end of the oblique surface. The two surfaces D1, D2 are formed 
approximately parallel to the movement direction of the left/right side 
plate 6. In accordance with the cam groove 6a shown in FIG. 6, the 
projection 11b which engages with the cam groove 6a on the left/right 
slide plate 6 slides in the forward/backward direction within the oblique 
surface D in the range of normal movement (i.e., when the forward/backward 
slide plate 11a moves within the range F in FIG. 1). 
However, when the left/right slide plate 6 is in a range of anomalous 
operation, the projection 11b is positioned in the range D1 or D2 at 
respective ends of the cam groove 6a. Therefore, since the projection 11b 
is positioned in a range D1 or D2 when the left/right slide plate 6 is in 
a range of anomalous operation, the projection 11b does not move in the 
forward/backward direction. Accordingly, the forward/backward slide plate 
11a does not move in the forward/backward direction within the ranges F1 
and F2 in FIG. 1, and the light emitting unit 11 does not move when the 
projection 11b is in the range D1 or D2. The range D of the cam groove 6a 
shown in FIG. 6 corresponds to the range of normal movement of the 
forward/backward slide plate 11a. 
Further, in accordance with the cam groove 6a shown in FIG. 6, an abnormal 
movement range of the light emitting unit 11 is considered to become 
unnecessary. The positional relationship of the forward/backward direction 
of forward/backward slide plate 11a and the light emitting unit 11 does 
not take into account an abnormal movement range, and may be set according 
to the necessary illumination angle. Because of the arrangement of the cam 
groove 6a, the path of movement of the light emitting unit 11 becomes 
short, and the flash device body 1 can be designed as a small-sized unit. 
Still further, in accordance with embodiments of the present invention, the 
rotation of the motor 3 is reduced via the gears 3a, 4a; however, the 
present invention is not limited to reducing the rotation of the motor 3 
using gears. For example, by using a stepping motor, or the like 
comparatively slow motor, the drive shaft 4 may be formed on the rotation 
axis of the motor 3. Accordingly, with the drive shaft 4 formed on the 
rotation axis of the motor 3, it is not necessary to provide the drive 
shaft 4 as a separate body, and the structure of the drive mechanism can 
be further simplified. 
Furthermore, in accordance with embodiments of the present invention, screw 
escape portions 4c, 4d are disposed at both ends of the drive shaft 4; 
however, the screw escape portions 4c, 4d are not limited to this 
arrangement, and, for example, a single screw escape portion may be 
disposed at any one end of the drive shaft 4. 
Moreover, in accordance with embodiments of the present invention, the 
light emitting unit 11 is moved to change the illumination angle; however, 
the present invention is not limited to moving the light emitting unit 11 
to change the illumination angle. For example, the illumination lens 13 
may be moved to change the illumination angle using a mechanism similar to 
that used to move the light emitting unit 11. 
In accordance with embodiments of the present invention, the transmission 
member advantageously does not move when the square nut 5 is beyond the 
screw threaded portion 4b because a screw escape portion 4c or 4d which 
provides a slip connection to the transmission member is disposed at at 
least one end of the drive shaft 4. Accordingly, damage to the variable 
illumination angle mechanism due to anomalous movement can be prevented 
with a simple construction. 
Moreover, a lock state of the drive mechanism is avoided because the drive 
shaft 4 is made to run idly, and damage to the drive mechanism and the 
like can be prevented. 
Furthermore, in the prior art slipping clutch, a predetermined static 
frictional force in the slipping surface being given, it was necessary to 
transmit the drive force normally. In contrast to the slipping clutch, 
with a screw escape device it is not necessary to transmit the drive force 
normally, and the friction with the transmission member can be designed to 
be extremely small. Accordingly, in comparison with a slipping clutch, the 
sliding frictional force arising in the contact surface of the screw 
threaded portion and the transmission member is small, and durability is 
greatly increased. 
Moreover, the sliding frictional forces used in both the drive and the 
drive shaft simultaneously become small, and the loads affecting these 
sliding frictional forces become small, and do not become the origin of 
breakdowns. 
Furthermore, in accordance with embodiments of the present invention, the 
ease of assembly of the flash unit is improved and the size of the flash 
unit is reduced because it is possible to simply form the screw escape 
portions where thread-shaped projections are not formed on the 
circumferential surface of the drive shaft. 
Still further, in accordance with embodiments of the present invention, 
because the flat spring 6c gives the transmission member an urging force 
toward the center of the drive shaft 4 accompanying the reverse rotation 
of the drive shaft 4, the transmission member positioned in a screw escape 
portion is easily put in threaded engagement with the drive shaft 4. 
Accordingly, by causing reverse rotation of the drive shaft 4, the 
variable illumination angle mechanism can be quickly returned to a state 
in which the illuminating angle can again be varied. The urging device can 
be realized with a simple construction comprising one spring member and 
two limiting members. 
In accordance with embodiments of the present invention, because the ends 
of the cam groove 6a of the translation cam are formed approximately 
parallel to the movement direction of the transmission member, when the 
transmission member moves to a screw escape portion 4c, 4d, the movement 
of the light emitting unit 11 or of the illuminating lens can be limited. 
Accordingly, the movement path of the light emitting unit 11 can be 
maintained, and the flash unit is not made large. 
In the above-described manner, a variable illuminating angle mechanism 
invention can be realized with a simple structure and high safety and 
durability. 
Although preferred embodiments of the invention have been shown and 
described, it will be appreciated by those skilled in the art that changes 
may be made in these embodiments without departing from the principles and 
spirit of the invention, the scope of which is defined in the appended 
claims and their equivalents.