GB1594653A

GB1594653A - Copy camera having automatic focusing

Info

Publication number: GB1594653A
Application number: GB493778A
Authority: GB
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1977-02-07
Filing date: 1978-02-07
Publication date: 1981-08-05
Also published as: DE2805030A1; JPS5713859B2; JPS5397418A

Description

(54) COPY CAMERA BEARING AUTOMATIC FOCUSING (71) We, DAINIPPON SCREEN SEIZO KABUSHIKI KAISHA, a Japanese Corporation, of 1-1 Tenjin-kitamachi, Teranouchi-agaru 4 chome, Horikawa-dori, Kamigyo-ku, Kyoto-shi, Japan do hereby declare that this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a copy camera having automatic focusing and a method of focuses the same.

When a manuscript is photographed or copied at a magnification m by a camera e.g. for plate making, supposing that the focal length of the lens used is f, that the distance between the manuscript and the lens is a, that the distance between the lens and the photo-sensitive materia used is b, and that the distance between the manuscript and the photo-sensitive material is c (which is equal to a plus b), the following equations must be satisfied for the image of the manuscrupt to be properly focused on the photo sensitive material: a=(l + l/m)f I b=(l+m)f II c=(2+m+1/m)f....III Usually, a camera for plate making includes a fixed film support, a movable lens support for supporting a lens, and a movable manuscript support for supporting a manuscript, the latter two supports being able to move on a frame which is arranged along the light axis of the lens.

Thus, in order to focus automatically at a desired magnification, the lens support and the manuscript support are so moved that all the supports occupy positions which satisfy the above equations II and III. In most cases, the positions of both the movable supports are determined, relative to the fixed film support, and thus each position of the lens support or the manuscript support is described by its distance from the film support.

In order to know the positions of the movable supports it is possible to set a standard point such as a fixed point which may be on the fixed film support or a certain distance away from it, and it is also possible rapidly to detect electric values corresponding to the absolute positions of the movable supports in proportion to the distances away from the standard point, without moving the movable supports.

The electric detector means for such ab solute positions may be an analog or a digital system. As regards the former, a system using electric resistors connected in parallel in a bridge form is well known. This system utilizes an anlogy between the formula for focusing a lens and the formula for parallel connection of resistors.

However, since this system employs resistors such as potentiometers, its linearity and resolution power are unsatisfactory and further it is difficult to adjust the circuit which handles the signals picked up from the resistors Thus, this is unreliable.

Regarding digital systems, a digital encoder is known, and particularly an absolute rotary encoder is generally used for detecting the absolute positions of the film supports. This includes a code disc plate with codes corres ponding to absolute positions thereof. The - code disc plate is rotated by a detecting shaft which is coupled to a position detector. The encoder puts out signals corresponding to the absolute positions of the supports by reading out the codes of the code disc plate by means of some pertinent means, for example, a de tecting head.

However, if its resolution power is to be made higher, the range of measurement is apt to be narrower because of the range of possible codes on the code disc plate.

Now in a camera for plate making, the measurement range is 1 to 3 meters and the resolution power required is at least 0.1 milli meter. It is therefore quite difficult in practice to make an absolute rotary encoder which can be applied in such conditions. Even if such an absolute rotary encoder can in principle be manufactured, this costs more than is accep table in a plate making camera.

Alternatively, an incremental rotary encoder is also known. This encoder, comprising a turn ing disc plate having slits arranged radially in its periphery, the slits being detected optically as a row of pulses, has a better resolution power and stability. Further, its measurement range may be freely selected and this type of encoder is of relatively lower cost.

This encoder puts out a number of pulses corresponding to the displacement of the turn disc plate and converts them into digital values.

However, this can not indicate directly the absolute position of the turn disc plate, instead only an indication of the relative position is given. Accordingly this can not be applied directly to the detector for the absolute position of the movable support.

Therefore, it is an object of the present invention to provide a method and apparatus for focusing a copying camera automatically, which is free from the above-mentioned defects and has better resolution power and reliability, a wide measure range and lower cost than prior art devices.

According to the present invention there is provided a method for focusing automatically producing a focused image in a copying camera which comprises a frame and a film support, a lens support, and a document support, at least one of which supports being movable, characterised in that: for each support are provided a counter, a quantisation device to which the movable support is connected, and a detect device, and that, ascertaining the momentary position of each movable support by first positioning it at a standard point, and then moving it, and calculating, as the support moves, the distance it has moved by counting, using the counter, pulses which are generated by the quantisation device, the counter being set to a standard count value when the detect device detects that the movable support is at the standard point, the movable support is moved to a desired position wherein the image of a document mounted on the document support is focused, by a lens mounted on the lens support, on a film mounted on the film support.

Preferably, at least two of the supports are movable, and the desired positions of these movable supports are calculated by an operation circuit, based upon the magnification desired for the focused image as set by a magnification setting device.

The invention also comprises an apparatus for focusing a copying camera automatically, said camera comprising a frame and a film support, a lens support, and a document support, which comprises: a position detector for one of the supports which is movable, positioned at a standard point in the range of motion of the movable support; an electric motor which drives a feed screw for moving the movable support; a movable support control circuit for controlling rotation, stopping, and rotational direction of the electric motor; a quantisation device for detecting the amount of motion of the movable support, which is connected to the feed screw; a position counter which counts pulses generated one per each quantisation unit by the quantisation device, up or down according to the direction of displacement of the movable support, to obtain a digital count value, and converts that digital count value into a position value relative to the standard point; and a comparison circuit which compares the desired position of the movable support with the position value of the position counter, to obtain a difference therebetween, and controls the movable support control circuit so as to reduce this difference to substantially zero.

Preferably, at least two of the supports are movable and there is further provided a magnification set device for setting the desired magnification, and an operation circuit which determines a desired position of the movable supports according to the magnification set by the magnification set device.

The present invention will now be described in more detail with reference to a preferred embodiment, illustrated in the accompanying drawings, but not limitative of the present invention, in which: Figure 1 is a schematic view of projection imaging; Figure 2 is a schematic view of an apparatus for focusing a copying camera automatically according to the present invention; Figure 3 is a block diagram of an operation circuit used in the apparatus of Figure 2; Figure 4 is a block diagram of a comparison circuit used in the apparatus of Figure 2.

Referring to Figure 1, a manuscript 1 is imaged on a photo-sensitive material 3 by a lens 2.

In Figure 2, there is shown a machine for focusing a copying camera automatically according to the present invention and adjusting, the magnitification thereof also. In order a detect the initial positions of a movable lens support 5 for supporting the lens 2 and a movable manuscript support 6 for supporting the manuscript 1, when the electric source is switched on, and before the copying camera starts photographing, the movable supports 5 and 6 are first positioned at standard points which are each a certain distance away from a fixed film support 4 which supports the photo-sensitive material such as a recording film or the like.

That is, prior to starting the copying camera, the lens support 5 is moved automatically towards the film support 4 along a feed screw 7 by an electric motor 11 and the manuscript support 6 is simultaneously moved automatically away form the film support 4 along a feed screw 8 by an electric motor 12.

When the lens support 5 contacts a micro switch 14 situated at the standard point for the lens support 5, the micro switch 14 sends a standard point detect signal to a control circuit 17. The control circuit 17 stops the motor 11.

The lens support 5 is set at the initial start position. This standard point detect signal is also sent to a position counter 19 for the lens support 5.

When the position counter 19 receives the standard point detect signal from the micro switch 14, the counter 19 is forcibly set to a standard digital value corresponding to the distance between the film support 4 and the standard point of the micro switch 14 irrespective of the previously counted value.

That is, the micro switch 14 is actuated and puts out the standard point detect signal. This standard point detect signal is then converted into the digital value corresponding to the distance between the film support 4 and the standard point of the micro switch 14 by an encoder for exclusive use for the standard point, in which the digital codes are predetermined corresponding to the distances set at the standard points. This digital value is converted into the count value of the position counter 19 synchronously with a standard zero pulse signal generated by a encoder 9.per one revolution thereof, which encoder cooperates with the lens support 5.

The encoder 9 cooperating with the lens support 5 and a encoder 10 cooperating with the manuscript support 6 hereinafter described are incrementary rotary encoders. Each encoder 9 or 10 is a quantizer for measuring as a digital value the distance moved through by the support 5 or 6.

The encoders 9 and 10 connected to the feed screws 7 and 8, respectively, which move the lens support 5 and the manuscript support 6 along the light axis of the lens. The encoders 9 and 10 quantize the feed distance corresponding to one revolution of the feed screw by the desired resolution power. The encoders each generate an electric pulse whenever displacement through a distance equal to the quantization unit occurs.

The electric pulses are counted by the counters 19 and 20 to obtain a counted value which corresponds to the displaced amount or the distance moved.

The moving directions of the supports 5 and 6 are detected and according to the detected directions the counters 19 and 20 count upwards or downwards.

When the lens support 5 reaches the micro switch 14, i.e., its standard point, the original position value is set, as described above. Thereafter the position of the lens support 5 can be known by the amount of displacement from the standard point.

Hence, if the standard point has its own predetermined value corresponding to the distance between the film support 4 and the standard point, the count value of the position counter 19 indicates the position of the lens support 5, that is, the distance of the lens support 5 away from the film support 4.

In the automatic operation hereinafter described, when the lens support passes through the standard point, the position counter 19 is adapted to be forcibly reset to the normal digital value which shows the distance from the standard point by the standard point detect signal coming from the micro switch 14 and the standard zero pulse signal generated by the encoder 9 per one revolution, and thus accumulated errors are automatically amended.

At the start of the operation, if the lens support 5 is positioned between the micro switch 14 and the film support 4, the lens support 5 moves all the way up to the film support 4, and contacts a micro switch 13 arranged at the upper end point of travel of the lens support 5, thereby actuating the micro switch 13.

An upper end point detect signal coming from the micro switch 13 is sent to the control circuit 17 which then rotates the electric motor 11 in reverse. Accordingly, the feed screw 7 for moving the lens support 5 is turned away from the film support 4. Then, the film support 5 actuates the micro switch 14 and sets the original position value and stops.

The manuscript support 6 is positioned at its initial position in the same manner as the lens support 5.

That is, there are provided a micro switch 16 for detecting the standard point of the manuscript support 6, a micro switch 15 positioned at the lower extremity of travel of the manuscript support 6, a control circuit for driving an electric motor 12, a rotary encoder 10 and a position counter 20.

The practical adjustments of the micro switches 14 and 16 for detecting their standard points will now be described.

When the copy camera is used, the standard points of the lens support 5 and the manuscript support 6 are preferably determined at the places which provide a magnification 1. This corresponds to actual-size copying, which is often used.

In this case, the positions of the lens support 5 and the manuscript support 6 to be set are determined in advance so that the manuscript attached to the manuscript support 6 may be focused accurately on a focusing screen mounte to the photo-electric material setting surface of the film support 4 at a magnification of 1 with the best possible resolution power of the projected image.

In this case, when both the supports 5 and 6 have been positioned at the correct predetermined positions, both the micro switches 14 ane 16 are then positioned so as to put out the standard point detect signals. The micro switche 14 and 16 are adjusted to mouni about at the center of the adjustment range in which the standard point detect signals are put out.

The encoders 9 and 10 are adjusted at phases in which the standard zero pulse signals are generated when the lens support 5 and the manuscript support 6 are located at the predetermined positions.

When the lens support 5 and the manuscript support 6 are moved and come again to the place which gives a magnification of 1, the standard point detect signals of the micro switches 14 and 16 and the standard zero pulse signals of the encoders 11 and 12 fix precisely the same positions of both the supports 5 and 6 as before.

The count values in the counters 19 and 20 at the abovedescribes standard point are the digital values (in binary codes) of the distances between the film support 4 and the lens support 4 and the lens support 5, and the film support 4 and the manuscript support 6 at magnification ofi.

If the resolution powers of the micro switches 14 and 16, i.e., the range of positions of the supports 5 and 6 where the standard point detect signals are put out, are slightly smaller than the distances corresponding to one revolution of the encoders 11 and 12, the actual resolution powers by which the micro switches 14 and 16 determine the standard points, are the same accuracy as those of the encoders 11 and 12 since the standard point detect signals are syn- chronized with the standard zero pulse signals of the encoders 11 and 12.

One embodiment has been hereinbefore described as being preset at a magnification of 1, but another magnification, for example, 2 may be possible.

Furthermore, the standard points are not necessarily determined on the basis of specific magnification rates, but may be arbitrarily determined, and further the number of standard points need not be restricted to one, but there may be several for each movable support, if necessary.

After setting the lens support 5 and the manuscript support 6 to the standard points respectively at the start of the operation, as described above, a magnification set device is set to the desired magnification and a start button for focusing is pushed.

In an operation circuit 22, from the magnification set in the magnification set device 21 and the focal distance of the lens used, which is set to a focal distance set circuit, the positions of the lens support 5 and the manuscript support 6 are calculated by a lens support position calculate circuit 27 and a manuscript position calculate circuit 28, each having a computation ability such as a micro computer according to the above-mentioned equations II and III.

Then, the lens support 5 and the manuscript support 6 start to move, each in the direction determined by the values of the position counters 19 and 20 and the calculation results of the operation circuit 22.

The count values of the position counters 19 and 20 are counted up or down and varied in succession from the initial values at the standard points, according to the displacements of the supports by the pulse signals for calculation which are generated by the encoders 9 and 10.

The count values of the counters 19 and 20 are compared with the desired values corresponding to the desired focusing positions of the lens support 5 and the manuscript support 6, calculated in the operation circuit 22, in comparison circuits 23 and 24, respectively.

In Figure 4 there is shown one embodiment of the comparison circuit 23. The binary count values of the position counters 19 and 20 are separated into three portions, a most significant byte, a middle byte and a least significant byte, comparison being made each.

Regarding the lens support 5 and the manuscript support 6, each comparison is performed in the same manner, and accordingly the case of the lens support 5 will be now described as follows: The values Al and B1 of the most significant bytes of the calculated result from the lens support position calculate circuit 27 and the count value of the position counter 19 are compared with each other.

If the values Al and B1 are not equal, the lens support 5 is moved in a predetermined direction according to the comparison of the values Al and Bl. When the values Al and B1 are equal, the values A2 and B2 of the middle bytes of the calculated result of the lens support position calculate circuit 27 and the count value of the position counter 9 are compared with each other.

When the values A2 and B2 are not equal, the moving direction of the lens support 5 is determined, as described above. When the values A2 and B2 are equal, the values A3 and B3 of the least significant bytes of the calculate circuit 27 and the count value of the position counter 19 are then compared with each other.

When the values A3 and B3 are not equal, the lens support 5 is moved in the predetermined direction, as mentioned above. When the values A3 and B3 coincide with each other, a coincidence signal is sent to the control circuit 17, thereby stopping the electric motor 11.

The lens support 5 and the manuscript support 6 are automatically located in the focal positions according to the magnification rate set in the magnification set device 21 in such a manner as described above. Then the exposure is carried out for the desired exposure period, and the manuscript attached to the manuscript support 6 is imaged and recorded on the photosensitive material attached to the film support 4 at the desired magnification.

If the manuscript is to be photographed at a different magnification, the new magnification is set in the magnification set device, and the start button is pushed.

The comparison of the count values of the position counters 19 and 20, which show the values corresponding to the present positions of the lens support 5 and the manuscript support 6, with the output values of the position calculate circuits 27 and 28 in which the desired focal positions of the lens support 5 and the manuscript support 6 corresponding to the new magnification rate are calculated, is performed and then the lens support 5 and the manuscript support 6 are automatically positioned at their new focal places, as described above.

Although there have heretofore been described in detail a preferred embodiment of this invention, it should be understood that various modifications are possible.

The components surrounded by a dotted line 25 in Figure 2 may be replaced by a computer such as a mini-computer or a microcomputer, the computer controlling the series of motions of the lens support 5 and the manuscript support 6.

Further, in the embodiment shown in Figure 2, the film support 4 is fixed and the lens support 5 and the manuscript support 6 are movable. However, any two of the three supports could be movable.

Further, if a zoom lens is used for the photographing camera, it is easily possible to practice the present invention using one movable support.

From the description above, it is readily understood that according to the present invention accurate positioning of the movable supports may be performed by using an incremental rotary encoder and the count errors of the position counters and noise influences may be minimized in such a manner that the count values of the position counters which vary in each case, are forcibly reset to the original value corresponding to each original position whenever the lens support of the manuscript support passes through its original position during automatic focusing.

WHAT WE CLAIM IS: 1. A method for focusing automatically producing a focused image in a copying camera which comprises a frame and a film support, a lens support, and a document support, at least one of which supports being movable, characterized in that: for each movable support are provided a counter, a quantisation device to which the movable support is connected, and a detect device, and that, ascertaining the momentary position of each movable support by first positioning it at a standard point. and then moving it, and calculating, as the support moves, the distance it has moved by counting, using the counter, pulses which are generated by the quantisation device, the counter being set to a standard count value when the detect device detects that the movable support is at the standard point, the movable support is moved to a desired position wherein the image of a document mounted on the document support is focused, by a lens mounted on the lens support, on a film mounted on the film support.

2. A method according to claim 1, wherein at least two of the supports are movable, and the desired positions of these movable supports are calculated by an operation circuit, based upon the magnification desired for the focussed image as set by a magnification setting device.

3. A method according to claim 2 wherein the quantisation device comprises an incremental rotary encoder.

4. A method according to claim 3 wherein the count value of the counter is converted into its own value at the standard point by synchronisini standard point detect signals with the pulses generated by the quantisation device by means of another quantisation unit which is larger than the quantisation unit used for detecting the amount of motion of the movable support when the movable support reaches the standard point.

5. An apparatus for focusing a copying camera automatically, said camera comprising a frame and a film support, a lens support, and a document support, which comprises: a position detector for one of the supports which is movable, positioned at a standard point in the range of motion of the movable support; an electrical motor which drives a feed screw for moving the movable support; a movable support control circuit for controlling rotation, stopping, and rotational direction of the electric motor; a quantisation device for detecting the amount of motion of the movable support, which is connected to the feed screw; a position counter which counts pulses generated one per each quantisation unit by the quantisation device, up or down according to the direction of displacement of the movable support, to obtain a digital count value, and converts that digital count value into a position value relative to the standard point; and a comparison circuit which compares the desired position of the movable support with the position value of the position counter, to obtain a difference therebetween, and controls the movable support control circuit so as to reduce this difference to substantially zero.

6. An apparatus according to claim 5 in which at least two of the supports are movable and there is further provided a magnification set device for setting the desired magnification, and an operation circuit which determines a desired position of the movable supports according to the magnification set by the magnification set device.

7. A method of focusing a copy camera substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. An apparatus for focusing a copy cameras substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. positioned at their new focal places, as described above. Although there have heretofore been described in detail a preferred embodiment of this invention, it should be understood that various modifications are possible. The components surrounded by a dotted line 25 in Figure 2 may be replaced by a computer such as a mini-computer or a microcomputer, the computer controlling the series of motions of the lens support 5 and the manuscript support 6. Further, in the embodiment shown in Figure 2, the film support 4 is fixed and the lens support 5 and the manuscript support 6 are movable. However, any two of the three supports could be movable. Further, if a zoom lens is used for the photographing camera, it is easily possible to practice the present invention using one movable support. From the description above, it is readily understood that according to the present invention accurate positioning of the movable supports may be performed by using an incremental rotary encoder and the count errors of the position counters and noise influences may be minimized in such a manner that the count values of the position counters which vary in each case, are forcibly reset to the original value corresponding to each original position whenever the lens support of the manuscript support passes through its original position during automatic focusing. WHAT WE CLAIM IS:

1. A method for focusing automatically producing a focused image in a copying camera which comprises a frame and a film support, a lens support, and a document support, at least one of which supports being movable, characterized in that: for each movable support are provided a counter, a quantisation device to which the movable support is connected, and a detect device, and that, ascertaining the momentary position of each movable support by first positioning it at a standard point. and then moving it, and calculating, as the support moves, the distance it has moved by counting, using the counter, pulses which are generated by the quantisation device, the counter being set to a standard count value when the detect device detects that the movable support is at the standard point, the movable support is moved to a desired position wherein the image of a document mounted on the document support is focused, by a lens mounted on the lens support, on a film mounted on the film support.