GB2235541A - Coil and magnet camera shutter actuating device - Google Patents

Abstract

A camera shutter has a fixed coil 1 and a rod 2 arranged therethrough a permanent magnet 3 is fast with the rod 2. A linkage 40,42 is provided between the rod 2 and the shutter blades 7,8 such that axial movement of the rod opens and closes the shutter. The rod 2 is normally biased to its closed position e.g. by lever 4 and spring 6, but energising the coil with a d.c. supply creates a magnetic field which attracts the magnet and opens the shutter. The biasing closes the shutter as soon as the d.c. supply is removed. Balance weight 5 is shown on lever 4. In an alternative arrangement Fig. 10 the rod is fixed and the coil is arranged to slide along it and is connected to the shutter blades. <IMAGE>

Description

CAMERA SHUTTER ACTUATING MECHANISM The present invention relates to shutters for use in cameras.

Several types of electronic shutter are known.

One type is shown in Fig. 1 of the attached drawings.

To take a photograph, release lever 10 is pressed. The operating lever 14 is then pulled to the left on account of the restoring force of the spring 15. The contactor 12 is connected simultaneously which initiates the electronic control circuit 20 that supplies electricity to the coil 18. The electricity makes the electromagnet set up an magnetic field and attract the iron plate 16. Following the left movement of the operating lever 14, the iron plate 16 moves to the left which pushes the shutter plate 24 to the left and the shutter plate 26 to the right. The moving of the shutter plates causes the shutter to open. When the electricity supply is cut off by the electronic control circuit 20, the electromagnet loses its magnetic field, and thus releases the iron plate 16. The tension spring 28 exerts a force on the shutter plates towards their original positions.The shutter is thus closed. This kind of electronic shutter design is the most popular ever built into electronic shutter cameras. Owing to its complexity and numerous components, the production cost is relatively high.

A second type is shown in Fig. 2 of the attached drawings. In this type when the shutter button 10 is pressed, the contactor 12 is connected. The electronic control part 20 then supplies electricity to the coil 18.

The induced magnetic field attracts one end of the operating lever 14, and rotates the operating lever 14 in a clockwise direction which allows the spring 19 to pull down the shutter lever 17. This moves the shutter plates 22 and 24 to the right and to the left respectively, opening the shutter. After the electricity supply is cut off by the electronic control part 20, the electromagnet loses its magnetic field and releases the operating lever 14. The spring 15 pulls the operating lever 14 back to its original position and thus closes the shutter plates. However, the accuracy of the exposure control of this kind of electronic shutter is poor and unreliable.

The third known type of shutter, shown in Fig. 3 of the attached drawings, comprises a printed circuit board (PCB) 32 inserted in a magnetic field provided by the magnetically conductive plates 34 and 36, the plane of the PCB 32 being perpendicular to the magnetic-field lines.

When taking photographs, the contactor 12 is pressed making a connection. The electronic control part 20 delivers electricity to the coil track on the PCB 32. The magnetic field between the conductive track and the magnetically conductive plates 34 and 36 generate a force pushing the coil towards the left and rotating the PCB 32 about axis 33 in a clockwise direction. This rotation moves the shutter plates 22 and 24 in opposite directions and thus opens the shutter. When the electricity supply is cut off by the electronic control part 20. The restoring force of the spring 15 gives the PCB 32 and anti-clockwise motion, and the shutter is closed. This kind of configuration occupies a larger space than is available in a simple camera.

Furthermore, the cost of the parts is high.

There are other known types of electronic shutter, but each has similar disadvantages: an excessive number of components, complex assembly procedures, large size and high component cost.

Furthermore, known shutters have the disadvantage that their mechanisms are not balanced so the forces on the shutter mechanism change as the angle of the camera is changed, leading to variations in exposure time.

According to the present invention there is provided a shutter actuating device for a camera, comprising an energisable coil, a permanent magnet mounted on the axis of the coil with its poles respectively proximal and distal to the centre line of the coil, the coil and magnet being arranged for relative movement along the coil axis between first and second positions in which the magnet is respectively axially further from and closer to the centre line of the coil, means for resiliently biasing the coil and magnet relatively towards the first position whereby energising the coil can overcome the biasing means and move the coil and magnet relatively into the second position, and a linkage for connecting the magnet or coil to a camera shutter so that the shutter is opened by relative movement of the coil and magnet into the second position; wherein the linkage comprises a lever being pivotally mounted and arranged such that the weight of the lever substantially balances the weight of the shutter mechanism regardless of of the angle of orientation of the camera.

These arrangements have the advantage that they provide an actuating device of comparatively few components that is easy to assemble and is compact yet is fully balanced and does not suffer from variations in exposure time as the camera angle in changed.

Preferably, the linkage between the moving part and the shutter blade is a peg, projecting from the moving, part in engagement with a slot in each shutter blade. The biasing means may comprise a balanced lever pivotally attached to the frame, one part of the lever bearing against the rod, the lever being biased such that the rod is urged to its first position.

Embodiments of the invention will now be further described by way of example, with reference to the accompanying drawings, wherein: Figure 4 shows the magnetic field patterns of a coil and a permanent magnet separated from each other; Figure 5 shows the magnetic field pattern of a coil and a permanent magnet as they approach each other; Figure 6 shows the field pattern of a coil and a permanent magnet whose pole dividing lines are coincident; Figure 7 is a diagramatic representation of the principle elements of a first embodiment of shutter having a moving permanent magnet; Figure 8 is a diagramatic representation of the principle elements of a second embodiment of shutter having a moving coil; Figure 9 is a perspective view partly cut away of a shutter of the first embodiment; and Figure 10 is a perspective view, partly cut away, of a shutter of the second embodiment.

Figure. 11 is a view of a shutter that does not have the balanced lever of the present invention; Figure 12 is a view of a shutter according to the present invention in a vertical position.

Figure 13 shows the gravitational forces acting as the balanced lever of a shutter according to the present invention.

Figure 14 shows the lines which act on the balanced lever of the present invention, including the forces of the spring and the shutter blades.

Referring to Fig. 4; a coil C is wound in the direction as shown. The positive (+) terminal of a DC battery is connected to end A of the coil, while the negative (-) terminal is connected to end B. The conducting coil creates a magnetic field, with S-pole on the left and the N-pole on the right the magnetic flux flowing from N to S pole as shown in the figure.

A permanent magnet M, coaxial with the coil C produces magnetic field lines as shown.

If the distance L between the coil C and permanent magnet M is great the forces generated by interaction of the magnetic flux systems are not strong. Both coil and permanent magnet will remain stationary. As the distance between the coil and the permanent magnet decreases the two magnetic fields merge to form a single unified force field as shown in Fig. 5. If the coil is fixed, the induced Npole of the coil will attract the S-pole of the permanent magnet and will exert a force pulling the permanent magnet towards the central core of the coil. The movement of the permanent magnet will continue until the pole-dividing line a-a of the coil overlaps with the pole-dividing line b-b of the magnet.The magnet will stop at this point where a completely unified magnetic field is formed by the interaction between the magnetic fields provided by the coil and the permanent magnet, as shown in Fig. 6.

Referring now to Figures 7 and 9 a coil 1 is fixed to frame 9. A sliding rod 2, which can slide along the axis of the coil 1, has a built-in permanent magnet 3 and a vertically protruding lever 40 which passes through a slot 42 cut in each of shutter plates 7, 8 which are pivotally attached to frame 9. The slots are shaped so that linear movement of the rod towards the coil 1 tends to close the shutter and movement away from the coil tends to open it.

A balanced lever 4, having a balance weight S engages the protruding lever 40 and a spring 6 biases the balanced lever 4 away from the coil, thereby keeping the shutter normally closed.

When a direct current flows into the coil 1, the induced magnetic field attracts the sliding rod 2 to the left which opens the shutter plates 7 and 8. When the power supply is cut off, the magnetic field of the coil 1 disappears. The restoring force of the spring 6 will then return the sliding rod to its original position and so close the shutter plates 7, 8.

The embodiment of Figures 8 and 10 is essentially similar to that of Figures 7 and 9, except that the coil 1 is wound on the sliding rod 2, while the permanent magnet 3 is fixed to the frame 9. Thus, it is the coil 1 that moves coaxially over the magnet 3 when the shutter is actuated.

The purpose of the balance lever 4 will now be described. In Fig. 9 a shutter similar to a shutter of the present invention is shown, without a balance lever.

If the camera is held such that the position of the electronic shutter inside it is as shown in Fig. 11, when the coil is connected with electricity, suppose the force to open the shutter is F; the weight of shutter plates 7 and 8 is GA and GB; the distance of the centre of the gravity to its plate movement axis AO and BO are Ka and and ( ( < a= < b=1); the weight of operating lever plus the weight of permanent magnet is G; and the attractive force is FC.

Then, F*L = (FC + G + 2GA - P) L GA = GB (1) F = FC + G + 2GA - P If instead the camera is held such that the position of the electronic shutter inside it is the inverse of that shown in Fig. 11, then the force (F) to open the shutter blades 7;8 is F^L = (FC - G - 2GA - P) L (2) F = FC - G - 2GA - P Therefore comparing (1) and (2), we know (1) f (2).

If the camera is held at different angles this will result in a different exposure value (EV) under the same light conditions.

Referring now to Figures 12 and 13, the effect of the balanced lever will now be explained. Figure 12 shows the balanced lever 4 and its pivot axis Go. The gravitational forces acting on the left-side of the lever 4, the right side of the lever 4 and the balance weight 5 are shown as G51, G52 and G5 respectively. The weight of the shutter and magnet acts as a force FT at a point K as before.

In Fig. 13a, force FT = G +2GA, and < ,is the distance from the axis Go at which this force acts. Force G52 acts at a distance 3 from the axis Go and force Go acts at the centre of gravity of the balance weight 5; a distance 4 from the axis 50. Figure 13b shows the resultant of the forces on the left and right side of the balanced lever 4, denoted FG and GF act respectively at distances (5 and < 6 from the axis 90. The lever is shown in a simplified form in Fig. 13c.

In order to be fully balanced the force couples on either side of the axis 50 must be balanced. This occurs when equation (3) below is satisfied.

SMGo = 0 FG . 5 - GF.(6 = 0 FG.(5 = GF.#6 (3) Where MGo represents force moments about axis Go.

Now assume that the camera is held at some angle e as shown in Fig. 13d.

Now the equations for balance become FG cos# .(5 - GF cos#.(6 = 0 FG cos# .#5 = GF cos## . #6 FG. < 5 = GF . #6 It can, be seen that this is the same as (3), and that tilting the camera will have no effect on the balance of the shutter.

Now consider the addition of spring (6) acting at point K, with the force P, where P = FG . #5 #1 (4) Then once again, balance all the force moments Go about the axis 90.

sMGo = 0 SMGo = F C1 + FG . #5 - PF - GF . #6 = 0 Therefore the force to open the shutter F2P. This system of forces is shown in Fig. 14.

Since FG.(5 = GF . #6 by formula (3) the shutter is in a balanced condition and its balance will not be affected by holding the camera at any angle (see Fig. 13d). Therefore to open the shutter, the force of spring P is the only force which needs to be overcome.

When F > P the shutter will open, when the force of F disappears, the shutter will close by the spring P.

Therefore the electronic shutter has a balanced lever (4) a balanced ball (5) and a spring (6). The function of these is to keep the exposure value unaffected by holding the camera at different angles, as shown in Fig. 15.

Claims (8)

CLAIMS:

1. A shutter actuating device for a camera, comprising an energisable coil, a permanent magnet mounted on the axis of the coil with its poles respectively proximal and distal to the centre line of the coil, the coil and magnet being arranged for relative movement along the coil axis between first and second positions in which the magnet is respectively axially further from and closer to the centre line of the coil, means for resiliently biasing the coil and magnet relatively towards the first position whereby energising the coil can overcome the biasing means and move the coil and magnet relatively into the second position, and a linkage for connecting the magnet or coil to a camera shutter so that the shutter is opened by relative movement of the coil and magnet into the second position; wherein the linkage comprises a lever being pivotally mounted and arranged such that the weight of the lever substantially balances the weight of the shutter mechanism regardless of of the angle of orientation of the camera.

2. A device according to claim 1 wherein the lever has a counterweight fast therewith, the pivot being between the counterweight and the connection between the lever and the shutter mechanism.

3. A device according to claim 1 or claim 2 wherein the coil is fixed to a frame and the rod is arranged for connection to the shutter.

4. A device according to claim 1 or claim 2 wherein the magnet is fast with a frame and the coil is arranged for connection to the shutter.

5. A device according to any one of claims 1 to 4 including shutter blades linked to the coil or magnet.

6. A shutter according to claim 5 wherein said linkage further comprises a peg projecting laterally from the rod in engagement with a slot in a said shutter blade.

7. A shutter according to any one of the preceding claims wherein said biasing means comprises a spring acting on the lever

8. A shutter actuating device substantially as described herein with reference to the accompanying drawings.