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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photographic apparatus and more
particularly to apparatus for controlling focus and exposure in an
automatic camera.
2. Discussion Related to the Problems
Automatic cameras are known which feature both automatic focus and
automatic exposure control. Typically, in such an automatic camera, an
electronic control circuit responsive to signals produced by input
transducers (usually photoelectrical devices such as photocells) produces
electrical control signals for controlling the camera mechanism by means
of electromechanical output transducers. An output transducer is required
for each camera function which is independently controlled. A very popular
type of output transducer is the servo motor. However, as the number of
automatically controlled camera functions increases to include, for
example, focus, aperture size, film winding and shutter cocking, the
corresponding proliferation of servo motors results in bulky and expensive
apparatus. A goal, therefore, has been to minimize the number of such
motors in the camera. An example of an automatic camera wherein one motor
controls focus, advances film and cocks the shutter is shown in U.S. Pat.
No. 3,917,395 issued to Ogawa on Nov. 4, 1975, and entitled CONTROL
CIRCUIT FOR PHOTOGRAPHIC APPARATUS.
In the apparatus shown by Ogawa, however, the aperture size cannot be
controlled independently of the exposure time. The relation between
aperture size and shutter time is determined by the mechanical design of
the shutter. Commonly assigned and copending U.S. Patent Application Ser.
No. 103,260 entitled METHOD AND APPARATUS FOR AUTOMATIC CONTROL OF A
PHOTOGRAPHIC CAMERA by Schauffele et al, filed on the same day as the
present application, discloses a technique and apparatus for determining
the optimum settings in a camera having an adjustable lens and adjustable
aperture size and shutter time. In an automatic camera employing this
technique, the aperture size and shutter time must be independently
controllable. The problem faced by the present inventor was to provide a
control mechanism in which all these adjustments are made automatically
and mechanically independently of each other while minimizing the use of
servo motors and the complexity of the apparatus.
SOLUTION--SUMMARY OF THE INVENTION
According to the invention, a control mechanism for use in a photographic
camera featuring automatic focus and automatic exposure control, including
independently controllable aperture size and shutter time, is built around
a multifunction control member which can be moved from an initial position
to a final position to initiate a photographic operation. A position
sensor associated with the multifunction control member provides a signal
representing the position of the control member as it moves. Both an
adjustable lens and a variable sized aperture have followers which follow
the movement of the control member to provide a range of focus positions
and aperture sizes. A lens arresting means such as an electromechanical
brake is adjusted, upon receipt of a focus control signal, to arrest
further movement of the adjustable lens, to determine thereby the focus
position. Similarly, an aperture arresting means, such as another
electromechanical brake, is adapted upon receipt of an aperture control
signal to arrest further movement of the variable sized aperture, to
determine the camera aperture. A control circuit receives the position
signal from the position sensor and produces the focus and aperture
control signals.
In a preferred embodiment of the invention, the position sensor associated
with the control member comprises a comb-shaped conductive track and a
wiper adapted to move relative thereto in response to movement of the
control member, to produce a series of pulses employed by the control
circuit for determining the position of the control member. The apparatus
further includes a shutter having a latch that opens the shutter in
response to movement of the control member to its final position. Also
featured is a means for returning the control member to its initial
position after a photographic operation and a means, responsive to the
return movement of the control member, for returning the lens and aperture
to their respective initial positions and for cocking the shutter.
DESCRIPTION OF THE DRAWINGS
The invention will be described with reference to the following drawings
wherein:
FIG. 1 is an exploded perspective view of a preferred embodiment of the
camera control mechanism according to the present invention;
FIG. 2 is a schematic circuit diagram showing a camera control circuit
comprising a microcomputer system and associated input and output
transducers for use with the camera control mechanism of the present
invention;
FIG. 3 is a block diagram of the camera control circuit shown in FIG. 2;
and
FIGS. 4-6 are flow charts showing the operation of the camera control
circuit shown in FIG. 3.
The Camera Control Mechanism
FIG. 1 illustrates a camera control mechanism according to a preferred
embodiment of the present invention. The mechanism includes a movable lens
element 50 having a pair of tabs 52 by which the lens element is
constrained to slide to and fro on a support rod 54. The lens element 50
is urged in a forward direction, as shown in FIG. 1, by a spring 56. A
crank 58 mounted on a pivot pin 60 includes a leg 62 with a forked nose
portion 64 which is adapted to engage a tab 65 on the side of the lens
element 50. The crank also has a ratchet sector 66 and an offset arm 68.
Nose 64 of crank 58 is urged into contact with tab 65 of lens element 50
by the engagement of arm 68 with a forearm 70 of a multifunction control
lever 71 arranged to pivot about a pin 72. Multifunction control lever 71
is so-called because the one lever is employed to determine the positions
of both the lens and an aperture, as described below. Control lever 71 has
a cam follower portion 74 which is urged into contact with a cam 76 by a
spring 78. The cam 76 is attached to a gear 80 which is arranged to be
driven by a motor 82 through a worm gear 84. As shown in FIG. 1, the lens
element 50 is held by control lever 71 through crank 58 in a far focus
position.
When motor 82 is energized to rotate cam 76 counterclockwise, as shown in
FIG. 1, spring 78 pivots the control lever 71 counterclockwise about pin
72, thereby moving forearm 70 away from crank arm 68, thus allowing spring
56 to urge the lens element in a forward direction toward a closer focus
position. A rear arm 85 of control lever 71 carries a wiper contact 86
which cooperates with a position sensor 88. The position sensor 88
comprises a comb-shaped control track 90 and a return track 92. Wiper
contact 86 provides a circuit path from the control track to the return
track each time a tooth of the comb is passed, thereby producing a series
of pulses which may be employed by a camera control circuit 91 to
determine the instantaneous position of lens element 50 while motor 82 is
running.
In operation, when a number of pulses corresponding to the desired position
for lens element 50 has been generated, an electromagnetic latch,
generally designated 93, is energized to arrest the forward travel of lens
element 50. The electromagnetic latch comprises an electromagnet 94
adapted to attract a pivotally mounted latch arm 96 toward its latching
position. A spring 98 is mounted to bias the latch arm away from its
latching position. When the electromagnet is energized, the magnet
attracts one end of the latch arm causing a tooth 99 on the opposite end
to engage ratchet sector 66 of crank 58, thereby stopping the lens at the
desired position.
After a picture has been taken, motor 82 is energized to rotate cam 76 and
return the control lever 71 to the position shown in FIG. 1. Forearm 70 of
the control lever engages and displaces crank arm 68 to return the lens to
its initial position. A switch 101 is positioned to be closed by the
returning extension 85 of control lever 71 to signal the control system to
stop the motor.
Behind the lens is a shutter mechanism having an opening blade 100 with a
circular aperture 102 and a closing blade 104 with a circular aperture
106. A spring 108 urges the opening blade to the right, as shown in FIG.
1, and another spring 110 urges the closing blade to the right. In the
initial closed position, as shown in FIG. 1, the aperture of the closing
blade is aligned with the optical path of lens element 50, but light is
blocked by the opening blade whose aperture is out of alignment with the
optical path. The opening blade 100 is held in the closed position by a
latch 112 which is urged toward its latching position by a spring 114. An
electromagnetic latch comprising a cantilevered keeper arm 116 and an
electromagnet 118 is adapted, when energized, to hold closing blade 104 in
the position shown in FIG. 1.
In operation, after forearm 70 of control lever 71 has moved sufficiently
to allow the maximum forward movement of lens 50, the forearm 70
encounters an upward extension 120 of latch 112, causing the latch to
pivot against the force of spring 114 to release the opening blade for
movement to the right under the influence of spring 108. The opening blade
travels to the right until the aperture 102 is aligned with the optical
path of lens element 50. A tab 122 on the opening blade encounters a
switch 124 which is positioned to be closed by the tab to signal the
automatic control system that the shutter is open and that motor 82 should
be stopped. Alternatively, switch 124 may be positioned to be closed by
forearm 70 just before latch 112 is released, to provide mechanical
compensation for shutter lag.
After a period of time determined by the camera control circuit 91,
electromagnet 118 is de-energized, thereby releasing closing blade 104 for
movement to the right under the influence of spring 110 to terminate the
exposure. Subsequently, motor 82 is restarted, causing cam 76 to complete
one full revolution, thereby returning the control lever to the position
shown in FIG. 1. Upon its return, forearm 70 of control lever 71
encounters an upward extension 126 on opening blade 100 to return the
opening blade to its initial position. Tab 122 of the opening blade picks
up closing blade 104 to return the closing blade to its initial position.
When the initial position is reached, spring 114 urges latch 112 into
latching engagement with opening blade 100.
An adjustable aperture, comprising a first aperture blade 128 and a second
aperture blade 130, is disposed directly behind the shutter. The two
aperture blades are constrained to move in opposite directions by a
walking beam 132 which is centrally pivoted and pinned at opposite ends to
the blades. Each of the blades has a teardrop-shaped opening, 134 and 136
respectively. When the aperture blades are in their initial position, as
shown in FIG. 1, the largest parts of the openings are in alignment to
provide the maximum effective aperture. A spring 138 urges walking beam
132 in a clockwise direction, as shown in FIG. 1, to form progressively
smaller apertures. The walking beam carries a tooth sector 140 which is
adapted to be engaged by a latch generally designated 142. The latch
comprises a pivotally mounted pawl 144 and an electromagnet 146. A spring
148 urges the pawl away from latching engagement with tooth sector 140.
When the electromagnet 146 is energized, the pawl is pulled into
engagement with the tooth sector to stop the aperture at the position
determined by the control system.
The aperture blades also possess a secondary set of apertures 150 and 152
which are disposed in the optical path of a photocell 154 to reduce the
light falling on the photocell as apertures 134 and 136 reduce the lens
aperture. The photocell is arranged to receive light from the scene,
preferably the central portion thereof where a main subject presumably
would be located. The aperture blades are held in their initial position
by engagement of the forearm 70 of control lever 71 with an upwardly
projecting portion 156 of the first aperture blade 128.
In operation, as lever 71 pivots in the counterclockwise direction, spring
138 causes blade 128 to follow forearm 70 of lever 71, thereby forming
progressively smaller apertures in alignment both with lens 50 and with
photocell 154. The aperture size is directly related to the number of
pulses produced by position sensor 88. When a predetermined position is
reached, the camera control circuit 91 energizes latch 142 to stop the
aperture in the desired position. After an exposure, forearm 70 of control
lever 71 returns the aperture to the maximum opening.
A body release member 158, which is accessible to the camera operator, has
a leg 160 which is adapted to engage a switch bank 162 when the body
release member 158 is depressed. The switch bank progressively supplies
power from contact 164 to contacts 166, 168 and 170, respectively. Contact
166 is connected to supply main power to the automatic control system.
Contact 168 is connected to the automatic control system to signal the
control system to compose a photograph by measuring the subject distance
and the subject brightness. Contact 170 is connected to signal the camera
control circuit 91 to complete a photographic operation. The camera
control circuit 91 receives inputs from the various switches and sensors
and controls the various solenoids in the apparatus shown in FIG. 1.
The Camera Control Circuit
Turning now to FIG. 2, there is shown an overall circuit diagram employing
a camera control circuit 91 for controlling the camera mechanism shown in
FIG. 1. Switches and other elements shown in FIG. 2 are similarly numbered
in FIG. 2.
Power for the circuit is obtained from a battery 174, the positive terminal
of which is connected to a main power switch 166. The main power switch
166, when closed, connects the positive terminal of the battery to a
positive bus 178. The negative terminal of the battery is connected to a
return bus 179. Positive bus 178 supplies power to the camera control
circuit 91. The return is provided to the camera control circuit by return
bus 179. The specific structure of a preferred embodiment of the camera
control circuit 91 will be described in further detail below.
A light-sensitive circuit 180 is connected between positive bus 178 and the
return bus 179. The light-sensitive circuit includes a photosensitive
element 154, such as a silicon photodiode, and suitable signal processing
eletronics for generating a signal proportional to the brightness B.sub.s
of the scene. The specific details of the light-sensitive circuit are not
shown because the circuit does not constitute part of the present
invention. Any number of light-sensitive circuits as employed in automatic
exposure control systems are suitable for use herein, the only requirement
being that the output signal of the circuit represent the brightness of
the scene. This scene-brightness signal is converted to a digital signal
suitable for use by the camera control circuit by an analog-to-digital
converter 182 and is supplied in digital form to control system 172 on
lines 184.
An automatic range-finding device 186 is also connected between positive
bus 178 and return bus 179. The specific details of the range-finding
device 186 are not shown because this device does not comprise a part of
the present invention. Several of the presently known automatic
range-finding devices are suitable for use herein. See, for example, the
sonic range-finding device disclosed in U.S. Pat. No. 3,522,764 entitled
RANGE FINDING AND FOCUSING SYSTEM FOR PHOTOGRAPHIC CAMERAS AND THE LIKE by
C. H. Biber, granted Aug. 4, 1970, or the solide-state range-finding
device disclosed in U.S. Pat. No. 3,945,023 entitled AUTO-FOCUS CAMERA
WITH SOLID-STATE RANGE FINDER by N. L. Stauffer, granted Mar. 16, 1976.
The range-finding device, when signalled by the camera control circuit 91
via line 188, determines the range to the main subject, i.e., that subject
which is in a principal part of the picture, preferably designated by
fiducial marks in the camera viewfinder. The range-finding device
generates a signal D.sub.s indicative of the distance to the main subject.
The distance signal is converted to a digital signal suitable for use by
the automatic control system by an analog-to-digital converter 190 and is
supplied in digital form to control system 172 on lines 192.
The control switch 124 which indicates that the shutter is open, the
control switch 168 which directs the camera control circuit to measure
scene light and subject distance, the control switch 170 which directs the
automatic control system to take a picture, and the position sensor 88
which indicates the relative position of control lever 71 are all
connected in parallel between positive bus 178 and the camera control
circuit. When closed, the respective control switches provide logic
signals to the camera control circuit.
Electromagnet 94 which activates the lens position latch, electromagnet 118
which holds the closing shutter blade latch, and electromagnet 146 which
activates the aperture position latch are connected between the positive
bus 178 and return bus 179 through the collector-to-emitter paths of
transistors 192, 194 and 196, respectively. The base electrodes of the
transistors 192, 194 and 196 are connected to the camera control circuit
91 through resistors 198, 200 and 202, respectively.
Positive bus 178 is also connected to one input of motor 82. The motor is
controlled by transistor pair 204 and 206 connected in a Darlington
configuration in the return leg of the motor circuit. The base of
transistor 206 is connected, through resistor 208, to the camera control
circuit. Switch 101 is mechanically coupled to the motor 82 via the
control lever 71 (see FIG. 4) and electrically connected to the positive
bus 178 for providing a signal to the camera control circuit 91.
The Camera Control Circuit
FIG. 3 shows the camera control circit 91 in more detail. The camera
control circuit, which interfaces with the camera control mechanism of the
present invention, is preferably embodied in a microcomputer 224 and its
associated input and output signal-conditioning circuits. Although a
microcomputer is described, it is to be understood that the control
circuit could also be a custom-designed circuit. The microcomputer 224
includes a stored program control memory 226, a temporary data storage
memory 228, a central processing circuit, i.e., a microprocessor 230, and
a timing and cycle control unit 232.
Programming a microprocessor, such as an INTEL 8008 or Model 8080
microprocessor (which can be used in accordance with the present
invention), is a skill well-understood in the art. The following
disclosure is written to enable a programmer having ordinary skill in the
art to produce an appropriate program for the computer. The particular
details of any such program would, of course, depend upon the architecture
of the selected computer.
Data input and output are performed sequentially under program control.
Input data are applied through an input signal buffer 234 to a multiplexer
236 or directly to central processing unit 230 through an interrupt signal
processor 238. The input signals to the input data multiplexer are derived
from the various control switches 124, 168, 170 and 101 (see also FIG. 2)
and the measured scene parameters are derived from analog-to-digital
converters 182 and 190. The input signal to the interrupt signal processor
is derived from position sensor 88. The output data and control signals
are applied to storage latches 240 which, in turn, provide suitable
control signals to output drivers 242. The output drivers are directly
coupled to leads which supply control signals to output devices such as
the motor 82 and electromagnets 94, 118 and 146. The automatic control
system functions are determined by a program stored in the computer
memory.
The program is located in the stored program control memory 226 which may
comprise a conventional read-only memory (ROM). The ROM contains the
operational program in the form of instructions and fixed binary numbers
corresponding to numerical constants. These data are permanently stored in
the ROM and are not altered by the computer operation.
Typically, the ROM 226 is programmed at the manufacturer's facility, and
the instructions programmed provide the required control functions as
described below. For a specific example, the total ROM capacity may be
approximately 2000 bytes, each byte being 8 bits in length.
The temporary memory 228 may be provided by a conventional random access
memory (RAM). RAM differs from ROM in two distinct characteristics:
(1) data stored in a RAM are destroyed by removal of power and
(2) the stored data are easily altered by writing new data into memory.
For example, the RAM capacity may be 256 bytes, each byte being 8 bits in
length. Data such as subject distance and scene brightness and computed
values for camera functions are stored in the RAM until the completion of
a photographic cycle. The RAM is also used to store intermediate data
generated by the computer in calculating the desired adjustments for the
camera functions.
Turning now to FIGS. 4-6, there is shown a flow chart for the operation of
the camera control circuit 91 (see also FIG. 1). To begin this operation,
the photographer depresses the body release member 158 which closes switch
166, thereby applying power to the camera control system. The first thing
which the computer 224 does is to determine, by sampling the input to the
microprocessor from switch 168, whether the photographer wants to compose
a picture. If switch 168 has been closed, a signal will be present at the
input and the program will continue. If not, the program will wait until
switch 168 is closed.
When switch 168 is closed, the computer senses the scene brightness by
sampling the output on lines 184 from the light-sensitive circuit 180. The
computer also senses the subject distance by applying a signal to line 188
to activate the automatic range-finder 186 and then samples the output on
lines 192.
Signals representing the scene brightness B.sub.s and subject distance
D.sub.s are stored in temporary memory 228. The computer then proceeds to
calculate the camera adjustments required for taking the picture.
The computer calculates the desired aperture and lens extension in terms of
counts from the position sensor 88 and the optimum shutter open time
T.sub.s. Count A represents the number of counts desired for the aperture
and Count L represents the number of counts desired for the lens. These
computed values are stored in temporary memory 228.
Proceeding to FIG. 5, the computer then checks to see whether a command has
been given to take a picture, by sampling the input from switch 170. If
the switch is open, the program waits until the switch is closed. When the
presence of a signal indicates that the switch is closed, the program
initializes a counter (by setting a variable COUNT=0) which will be used
in setting lens and aperture positions. Next, the computer energizes the
shutter holding magnet 118 so that the shutter will not close as soon as
it is opened. The computer then starts motor 82 by activating the data
storage latch which controls the output driver for the motor.
As the motor rotates cam 76 (see also FIG. 1) counterclockwise, cam
follower 74 allows the multifunction control lever 71 to rotate
counterclockwise under the influence of spring 78. The aperture and lens
follow the motion of the multifunction control lever through their
respective mechanical linkages. As multifunction control lever 71 moves,
pulses are generated by the position sensor 88. Each pulse which is
received by the computer from the position sensor causes a transfer to the
interrupt routine shown in FIG. 5. The interrupt routine increments COUNT
by 1 and then returns control to the place in the main program where the
interrupt occurred. Meanwhile, the main program checks to see which is the
larger, COUNT A or COUNT L.
If COUNT A is the larger, the program checks to see whether the lens has
been stopped yet. At this stage of the operation, of course, the lens has
not yet stopped but, as will be seen, this check is used later as a means
of getting out of this portion of the program. Next, the computer checks
to see if COUNT equals COUNT L. When it does, the computer causes the lens
to stop by energizing electromagnet 94, thereby causing latch 93 to
inhibit further motion of crank 58 to stop the lens at the desired
position.
The computer then checks to see if the aperture has been stopped. Because
COUNT A is larger than COUNT L in this example, of course, it has not; but
this check is used to enable the program to continue after both the lens
and the aperture have been set. The computer then checks to see whether
COUNT is equal to or greater than COUNT A. When it is, the computer stops
the aperture by applying a signal to the output drive which energizes
electromagnet 146, thereby causing latch 142 to arrest further movement of
the aperture. Next, the computer again checks to see whether the lens has
previously been stopped. If it has been, the computer continues with the
main program. Similarly, if COUNT A had been greater than COUNT L, the
computer would have first set the aperture, then the lens, then continued
as shown in FIG. 4. Subsequent interrupts caused by the pulses from sensor
88 continue to increment the COUNT but have no further effect on the
execution of the main program.
Proceeding to FIG. 6, after the lens and aperture have been set, the
computer waits for the shutter to open. This is indicated by a signal from
switch 124. Upon receiving the signal that the shutter has opened, the
computer stops the motor by removing the drive signal to the motor control
circuit and intitiates an internal timing cycle by setting a variable T=0.
Then the computer goes into a sequence of repeatedly incrementing T by 1
count and checking to see if it is time to close the shutter. When the
proper time T.sub.s arrives, the computer signals the shutter to close.
The computer then prepares the apparatus for the next photographic cycle by
de-energizing the lens-electromagnets 94 and 146. Motor 82 is then started
to return the multifunction control lever 71 to its initial position. When
the control lever reaches its initial position, the computer is signalled
by the closing of switch 101 and the motor is stopped. The motor may also
be coupled to a film advance mechanism adapted to advance film during this
portion of the motor cycle.
The invention has been described in detail with reference to a preferred
embodiment. Obviously, numerous modifications and variations are possible
within the spirit and scope of the invention. For example, the
multifunction control member 71 could be adapted to slide rather than
pivot, or lens and aperture latches 93 and 142 could comprise various
other latching means such as magnetic brakes.
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