Method and apparatus for automatically compensating for rotation of images in articulated optical systems

In articulated optical systems, rotation of the image takes place due to the articulations. The invention eliminates this disadvantage by producing a signal whose polarity is dependent on the direction of rotation in which the image produced in the observation plane (64) is turned with respect to the object. By the signal, a compensation element (72) arranged in the articulated optical system is turned until the signal has disappeared. Two devices are disclosed for producing the signal: 1. At the start of the articulated optical system a mark (16) is introduced by reflection, it being focused at the end of the articulated optical system on a sensor (67). 2. On all articulations there are arranged position transmitters (111,112, etc.) which are connected with a minicomputer (130) which calculates the resultant image rotation and gives off a corresponding signal via a digital analog converter (131).

BACKGROUND OF THE INVENTION 
The present invention relates to both a method and an apparatus for 
compensating for the image rotation produced by relative movement of the 
various parts of an articulated optical system which consists of members 
having lenses for optical focusing as well as articulations with mirrors 
or prisms for deflecting the ray path. 
Articulated optical systems are used, for instance, in conjunction with 
operation microscopes and endoscopes in order to attach to such 
microscopes or endoscopes devices for simultaneous observation and/or 
documentation, e.g. still cameras, motion picture cameras, or television 
cameras. In this case it is desirable to relieve the operation microscope 
or endoscope from all the accessories so that it can be moved as easily as 
possible in all directions. The simultaneous- observation and 
documentation devices are therefore fixed on a special supporting arm and 
are connected flexibly with the operation microscope or endoscope. For 
this purpose, there are used articulated optical systems which consist of 
members with lenses for optical focusing which are connected by 
articulations in which mirrors or prisms deflect the ray path. Various 
members are able to move relative to each other telescopically or 
rotationally, or both. The disadvantage of known articulated optical 
systems resides in the fact that the displacement of the operation 
microscope or endoscope and the change in the articulations caused thereby 
causes the image to be rotated. This rotation of the image can be 
compensated by suitable optical elements, but the known devices, in which 
this must be carried out by hand, require an amount of handling which is 
excessive in practice. 
In West German unexamined patent application (offenlegungsschrift) 27 54 
614 there is described an articulated optical system in which the image 
rotation is automatically compensated by connecting the articulations with 
each other by mechanical transmissions, and in each member there is 
provided an additional reflection prism which is turnable by gears around 
its longitudinal axis. Such an articulated lens system is very demanding 
in mechanical and optical respects, particularly if space for manipulation 
in all directions is desired for the operation microscope or endoscope and 
numerous articulations are thus necessary. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a method and an apparatus 
which precisely compensate automatically, with little expenditure of 
means, for the rotation of the image, particularly in articulated optical 
systems having a large space for manipulation in all directions, i.e. 
having a large number of articulations. 
The method of the invention comprises the production of a signal whose 
polarity is dependent on the direction of rotation of the image produced 
in the plane of observation with respect to the object. Controlled by that 
signal, a compensation member arranged in the ray path of the articulated 
optical system is actuated until the signal disappears. 
One apparatus for the carrying out of this method is characterized by the 
facts that a mask is mirrored in an intermediate image plane in which the 
intermediate image produced there has a defined position relative to the 
object, and that a sensor for the image of the mark is arranged in fixed 
position in the intermediate image plane in which the intermediate image 
produced there is to have a defined position relative to the observation 
device, and also that the sensor is connected via a circuit to a 
servo-motor for turning the optical compensation element. 
The mirroring-in of a mark can be effected, for instance, by a light guide 
which is bevelled at the angle of 45.degree.. As source of light for the 
mark, infrared radiators or light-emitting diodes, for example, can be 
used. The wave lengths of the optical radiation which extends from the 
mark and the wave lengths to which the sensor is sensitive can be 
optimally adapted to each other by filters. They may also be so selected 
that the mark is invisible to the human eye. The mark can also be produced 
by providing a small hemisphere of optical material which deflects all 
light rays of the intermediate image impinging upon it to its center, 
which is arranged in the first intermediate image plane. This bright 
center-point is then focused on the sensor. Another possibility consists 
in arranging in the first intermediate image plane a mark which is opaque 
to that radiation to which the sensor is sensitive. The sensor then reacts 
to a dark mark. In a preferred embodiment, a dove prism is used to 
compensate for the image rotation. 
The advantages obtained by the invention include, in particular, the fact 
that the expense for the automatic compensating for the rotation of the 
image is independent of the number of articulations and this is slight 
even in articulated optical systems having a large number of 
articulations. Furthermore, no mechanical or optical tolerances enter into 
the precision of the compensation, since the precision depends merely on 
the sensitivity of response of the sensor. 
The method of the invention can also be carried out by means of a device in 
which all articulations are connected to angular-position transmitters 
which are connected, via circuits for the processing of the signal, to a 
minicomputer which, from the signals of the angular position transmitters, 
produces a signal which is proportional to the total rotation of the 
image. The output of the minicomputer is connected to a servomotor for the 
rotation of the optical compensation element. 
In a preferred embodiment of this solution, the optical element for 
compensating for the rotation of the image is also connected to an angular 
position transmitter whose position is fed, after signal processing, also 
to the minicomputer, which compares the actual value with the calculated 
desired value and gives off a correction signal to the servomotor via a 
circuit. 
The advantage of this solution is that, even upon being turned on, and with 
rapid, wide rotations of the articulations, the optical element for the 
compensation is always reset on the shortest path. Since only one 
(relatively simple) angular position transmitter including signal 
processing is necessary for each articulation, the expenditure remains 
within reasonable limits in articulated optical systems having numerous 
articulations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an articulated optical system which is developed as a 
turn-push articulated optical system, various tubular members of which may 
be moved axially or telescopically relative to each other, as indicated 
schematically by the straight arrows 8, or may be turned relative to each 
other, as indicated schematically by the curved arrows 9. However, the 
details of construction of the articulated optical system are not part of 
the present invention, and may be varied widely so far as the present 
invention is concerned, except as may be specifically noted or implied 
below. The mechanical construction of the articulated optical system here 
illustrated, apart from the means for automatically compensating for image 
rotation, is a separate invention. 
For the present invention it is of importance that in the ray path divided 
out by the cube splitter 10 from the ray path of an associated optical 
instrument, such as an operation microscope or endoscope, a real 
intermediate image is formed in the plane 15 by the lenses 12 and 13. This 
intermediate image still has a well-defined position with respect to the 
associated optical instrument such as the operation microscope or 
endoscope, since the tube 11 is rigidly connected to the optical 
instrument (not shown). The intermediate image 15 contains, according to 
the present invention, a mark 16. This image together with the mark 16 is 
focused by the lenses 23, 32, and 52 via the mirrors 22 and 42 into the 
next intermediate image plane 53. The latter is focused, via the lens 55, 
and the mirror 56, an optical element for image rotation 72, the cube beam 
splitter 62, and the lens 65, onto the image plane 66 of a documentation 
device as well as via the lens 63 into an observation plane 64. The image 
plane 66 may represent the image plane of any desired documentation 
device, such as a television camera, a motion picture camera, or a still 
camera. The image plane 64 may represent a viewing or observation screen, 
as well as being used for the location of a sensor in or just outside of 
the image area 64, as described below. The image planes 66 and 64 have 
well-defined positions with respect to the documentation and 
simultaneous-observation device or devices. 
In these planes the image, independently of the position of the 
articulations, should correspond, with respect also to its orientation, 
precisely to the initial image. In order to achieve this, notwithstanding 
the image rotation or twist caused when the members of the articulated 
system are turned relative to each other, a sensor 67 is arranged in the 
plane 64, and in front of the cube divider 62 there is an optical image 
rotating element 72 which can be turned around its optical axis via a 
gearing 73 by the motor 74. 
The functional development of the automatic compensation for the image 
rotation is shown schematically in FIG. 2. In the intermediate image plane 
15 the mark 16 is located within or outside of the intermediate image, 
preferably outside as here illustrated. Behind the articulated optical 
system 44 and the optical element 72 for compensation for the image 
rotation there is the observation plane 64 with the sensor 67, on which an 
image 68 of the mark 16 is focused. If this mark differs from the zero 
position, then the sensor 67 produces a signal. In the signal processor 78 
a signal for the control of the servoamplifier 79 is produced therefrom. 
The servo-amplifier 79 controls the motor 74 which, via the gearing 73, 
turns the optical element 72 for compensation of the image rotation until 
the image mark 68 is again in the zero position. The image rotating 
element 72 is conveniently a dove prism. 
FIG. 3 shows the corresponding circuit. As this circuit diagram is a long 
one, it has been divided into two parts 3a and 3b which should be placed 
end to end to visualize the entire circuit. Thus the point 87 at the right 
end of FIG. 3a is the same as the point 87 at the left end of FIG. 3b. 67 
is again the sensor, which is preferably developed as a differential 
photo-diode. The amplifiers 80 and 81 are controlled by it. The signal of 
the amplifier 80 is turned 180.degree. in phase in the amplifier 82 so 
that a photo-signal which is dependent on direction and has a positive or 
negative potential with respect to ground is produced at the circuit point 
83. When the image mark 68 is in the center of the differential 
photo-diode 67, the difference photo-signal is practically zero. Upon slow 
migration of the image mark 68 on the other hand, a direction-dependent 
voltage is produced which passes, via the closed FET switch 84 and a 
high-ohmic voltage follower 86, to the servo-amplifier 79, which controls 
the motor 74 as a function of direction and thus turns the dove prism 72 
as a function of direction via the gearing 73. 
Upon a rapid or sudden movement of the articulated optical system, the 
image mark 68 first leaves one field of the differential photo-diode and 
fully strikes the other field. This results in a maximum value of the 
difference photo-signal. In this case, the comparator 90 responds. This 
comparator consists of the amplifiers 91 and 92, a variable resistor 93 
for the threshold value, and the OR gate 94. When the amplified 
photo-signal of one of the two photo-diode halves drops below the 
threshold value, the comparator 90 opens the FET switch 84. As long as the 
FET switch is open, the last difference photo-signal is stored in the 
capacitor 85 and the servoamplifier 79 continues to receive a control 
signal for the opposite direction, in which the image mark has left the 
differential photo-diode, until the threshold value is again exceeded, 
i.e. until the image mark again covers both halves of the differential 
photo-diode and thus the direct adjustment of the dove prism 72 takes 
place. 
Upon the turning on of the system it is improbable that the image mark will 
lie on the differential photo-diode. Therefore, when turned on, the 
storage capacitor 85 is charged in principle, via a differentiating member 
consisting of the resistor 95 and the capacitor 96 by a pulse of 
predetermined length. The FET switch 84 is opened until the image mark 68 
covers both halves of the differential photo-diode 67. 
The mirroring-in of the mark takes place, in one advantageous embodiment of 
the invention, by a light guide which is arranged perpendicular to the 
optical axis and is bevelled at an angle of 45.degree. to the optical 
axis. In this case, the light guide acts at the same time as cylindrical 
lens so that a bevelled illuminated end surface is imaged as a thin line. 
FIG. 4 shows the basic circuit diagram for another solution for the 
automatic correction of the image rotation caused by movement of the 
articulations. On all articulations there are angular-position 
transmitters 111, 112, etc., whose position is fed to signal processing 
units 121, 122 etc. The signals processed there are forwarded to a 
minicomputer 130 which, from the individual signals, determines the 
resultant rotation of the image. The output values of the minicomputer 
which are obtained in close time sequence are fed to a digital-analog 
converter 131 which produces a voltage which corresponds to the position 
of the optical element 72 necessary in order to compensate for the image 
rotation. In one advantageous embodiment, this element is also connected 
to an angular position transmitter 141 whose position indication, after 
going through a similar processing unit 142, is also fed to the 
minicomputer. The latter continuously compares the actual value with the 
calculated desired value and gives off corresponding correction signals, 
via the servoamplifier 79, to the servomotor 74 which is connected via the 
gearing 73 with the optical element for compensating for the image 
rotation 72. After a signal zero-positioning of the reset prism, each 
image rotation is thus automatically corrected as a result of the rotation 
of the articulations. 
In another embodiment, an analog signal is produced in the signal 
processing unit 142 and fed as an actual signal to a comparator. The 
comparator compares this signal with the desired analog signal and gives 
off a corresponding correction signal to the servomotor 74 via the 
servoamplifier 79. 
One example of an arrangement for the coupling of the articulated optical 
system described to an optical instrument such as an operation microscope 
is shown in FIG. 5. 201 is the objective of the instrument, which is 
seated in the housing 202. Behind the objective there is arranged the cube 
splitter 10 known from FIG. 1, by which a part of the ray path is branched 
off into the articulated optical system which, at the start, comprises the 
tube 11 and the lens 12. This type of coupling is also suitable for stereo 
operation microscopes and endoscopes. The cube splitter 10 is seated in 
one ray path and a corresponding cube splitter, to which other devices can 
be connected, is arranged in the second ray path. 
One disadvantage of this coupling is the relatively large loss of light due 
to the cube splitter. As a result, either the observation image becomes 
darker or the intensity of illumination of the object must be 
correspondingly increased. 
This disadvantage is avoided in stereo operation microscopes or endoscopes 
by the arrangement shown in FIGS. 6 and 6a. In this case the ray path for 
the articulated optical system is branched off in front of the objective 
201 by a mirror or prism 203 which is arranged between the two entrance 
pupils 204 and 205 of the stereo observation ray paths of the microscope, 
as shown most clearly in FIG. 6a, an end view. In order not to bring the 
end of the articulated optical system too close to the object, a 
deflection is effected via two mirrors 206 and 207. In front of the prism 
there is arranged an objective 208 which takes over the role of the 
objective 201 for the branched-off ray path. This objective can also be 
arranged further back in the ray path, for instance between the mirrors 
206 and 207. 
In operation microscopes, the objective designated 201 in FIGS. 5 and 6 
directly images the object. In the case of endoscopes on the other hand 
the branching off of the ray path for the articulated optical system 
generally takes place at the end of the apparatus. The objective 201 then 
does not image the object itself, but rather an intermediate image of the 
object. 
Another possibility for coupling the articulated optical system is shown in 
FIG. 7. Here the ray path for the articulated optical system is taken off 
in front of the objective 201 and as a matter of fact, as close as 
possible alongside the entrance pupil of the objective 201 at a different 
angle directly from the object 213, and is introduced via the mirror 211 
into the articulated optical system. The objective 212 assumes the role of 
the objective 201 for the articulated optical system.