Driving device for a revolver in a microscope

A microscope provided with a revolver having objective lenses mounted thereon and rotatable to move the objective lenses into an observation optical path comprises means for varying the load torque for rotation of the revolver at the rotated position of the revolver when the objective lenses face a predetermined position in the observation optical path, an electric motor, circuit means for driving the electric motor, means for transmitting the rotation of the electric motor to the revolver, and means for detecting the fluctuation of the load of the electric motor caused by a variation in the rotational torque of the revolver, and means for acting on the circuit means to stop the rotation of the electric motor in response to the detecting means.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a revolver for mounting the objective lenses of a 
microscope thereon, and in particular to a driving device for rotating the 
revolver for the interchange of the objective lenses. 
2. Description of the Prior Art 
Heretofore, in a microscope, a plurality of objective lenses have been 
mounted on an objective revolver and the magnification of the objective 
lenses has been changed by manually rotating the objective revolver. 
However, the objective revolver normally overlies a sample to be observed 
and therefore, when the objective revolver is manually operated, minute 
dust may drop from the hand onto the sample. Particularly, during the 
observation of a semiconductor wafer or the like having a minute pattern 
of the order of one micron, even such dust forms a problem and therefore, 
a microscope in which the rotation of the objective revolver is 
accomplished manually has not been preferable. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a microscope in which 
the rotation of the objective revolver is automatized. 
It is another object of the present invention to provide a driving device 
for electrically rotating the objective revolver and for automatically 
stopping the revolver at a position whereat one of objective lenses is 
aligned with respect to the optical axis. 
The invention will become fully apparent from the following detailed 
description thereof taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, there is shown an embodiment of the present 
invention. In FIG. 1, an objective revolver 11 is supported for rotation 
about an axis P relative to a fixed portion of the body, not shown, and 
has four mounts 10a, 10b, 10c and 10d for mounting objective lenses. The 
inner peripheral surface of the revolver 11 has clicking recesses 11a, 
11b, 11c and 11d corresponding to the respective mounts, and a click ball 
12 biased by a spring 13 is adapted to be received into these recesses 11a 
to 11d from the device body. By the click ball 12 being received in the 
recesses 11a to 11d, objective lenses corresponding to these recesses are 
aligned with an observation optical axis L. The circumference of each 
recess protrudes from the inner peripheral surface of the revolver toward 
the rotational axis P and the click ball 12 is received into the 
respective recesses beyond the sloping surfaces formed by the 
protuberances. A belt 14 as a power transmitting means is extended between 
the outer periphery of the revolver 11 and a pulley 15 rotated by a motor 
23. 
FIG. 2 shows an electric device for controlling the drive of the motor. An 
operation device 20 has switches extraneously operable to put out a 
revolver rotation start signal RS and a revolver rotational direction 
indicating signal RI. More specifically, it has, for example, a switch for 
indicating the clockwise rotation of the revolver and a switch for 
indicating the counter-clockwise rotation of the revolver. Design may be 
made such that when the switch for indicating the clockwise rotation is 
closed, the clockwise rotation indicating signal RI is first put out to a 
predetermined terminal and thereafter the rotation start signal RS is put 
out, or there may be provided a clockwise rotation indicating signal 
outputting switch, a counter-clockwise rotation indicating signal 
outputting switch and a rotation start signal outputting switch. The 
signals RS and RI from the operation device 20 are applied as inputs to a 
driving circuit 21 capable of controlling the motor in both directions. 
The rotation start signal RS is also applied as input to a timer circuit 
22. When the signal RS is applied as input to the driving circuit 21, this 
circuit supplies the motor 23 with a current of a predetermined direction 
indicated by the signal RI. The load current of the motor 23 is detected 
by a detecting circuit 24. The detecting circuit 24 produces a voltage 
output VO variable correspondingly to the variation in the load current. A 
waveform shaping circuit 25 threshold-processes the output voltage VO of 
the detecting circuit 24 at a predetermined level and waveform-shapes this 
output voltage. On the other hand, the timer circuit 22, as will be 
described later, puts out a time-up signal Tu as early as possible after 
the lapse of the time necessary for the click ball 12 to ride over the 
protuberance 11a' around the recess 11 a of the revolver to be disengaged 
from the recess 11a in which the click ball 12 is presently fitted after 
the rotation start signal RS has been put out. An AND gate 26 causes the 
output signal 01 of the waveform shaping circuit 25 when the time-up 
signal Tu is being produced to be applied as input to a monostable 
multivibrator 27 and a pulse generating circuit 28. The pulse generating 
circuit 28 makes a stop pulse Ps from the signal OUT2 of the AND gate 26 
and the signal OUT3 of the multivibrator 27 and applies it as input to the 
driving circuit 21. The driving circuit 21 stops the supply of current to 
the motor 23 in response to the stop pulse Ps. 
Such operation will hereinafter be described with reference to FIGS. 3A and 
3B. 
In FIG. 3A, for convenience of illustration, it is assumed that the click 
ball 12 moves relative to the revolver 11. First, consider a case where 
the click ball 12 is received in the recess 11a of the revolver 11. When 
the operation device 20 is instructed to rotate the revolver 11 in 
counter-clockwise direction, the driving circuit 21 rotates the motor 23 
in the direction therefor. This rotation of the revolver is equivalent to 
rightward movement of the click ball 12 as viewed in FIG. 3A if it is 
assumed that the revolver 11 is stationary. When the click ball 12 comes 
out of engagement with the recess 11a, a great load current flows to the 
motor 23 due to the increase in resistance resulting from the biasing 
force of the spring 13 and therefore, the output voltage VO of the 
detecting circuit 24 is increased. When the click ball has come out of the 
recess 11a, the load of the motor becomes stable at a relatively small 
value. When the click ball climbs up the sloping surface 11b' forming the 
protuberance around the next recess 11b, the load is increased and thus, 
the output voltage VO of the detecting circuit is increased. When the 
click ball drops into the recess 11b, the load of the motor is decreased. 
When the click ball 12 comes out of engagement with the recess 11b, a 
great load current again flows to the motor and therefore, the output 
voltage VO of the detecting circuit is increased as indicated by broken 
line in FIG. 3B. Since the waveform shaping circuit 25 threshold-processes 
the output voltage VO of the detecting circuit 24 at a predetermined level 
V.sub.ref, the output signal OUT1 is produced when the click ball comes 
out of engagement with the recess 11a, when the click ball climbs up the 
sloping surface 11b' and when the click ball comes out of the recess 11b. 
Since the timer circuit 22 puts out a high level time-up signal TU in a 
sufficient time required for the click ball 12 to come out of the first 
recess 11a after the motor starts to rotate, the AND gate 26 first puts 
out the output signal OUT1 which is obtained when the click ball climbs up 
the sloping surface 11b' of the recess 11b. This signal is a signal OUT2 
indicative of the fact that the revolver 11 has been rotated by a 
predetermined amount. At the moment when the click ball 12 completely 
climbs up the sloping surface 11b', the value of the output voltage VO of 
the detecting circuit reaches its peak and therefore, the falling of the 
signal OUT2 indicates that the click ball 12 is at a certain position in 
the course of its downward movement after it has completely climbed up the 
sloping surface 11b'. The monostable multivibrator 27 and the pulse 
generating circuit 28 prepare the stop pulse PS for stopping the supply of 
current to the motor upon this falling. That is, the multivibrator 27 puts 
out a pulse output OUT3 of a predetermined time width in response to the 
rising of the output signal OUT2 of the AND gate 26. On the other hand, 
the pulse generating circuit 28 prepares an inverted signal INV of the 
output signal OUT2 of the AND gate 26 and also prepares the stop pulse PS 
by the AND of the pulse output OUT3 of a predetermined time width and the 
rising of the inverted signal INV, and applies it to the driving circuit 
21. As a result, the driving circuit 21 cuts off the supply of current to 
the motor 23. Accordingly, the motor 23 rotates due only to its inertia 
and the click ball 12 naturally drops into the recess 11b due to the 
inertial rotation of the motor and the biasing force of the spring 13 and 
becomes stable in its dropped state. As a result, the rotation of the 
revolver 11 is stopped at a position whereat the optical axis of the 
objective lens 10b is coincident with the observation optical axis. 
The timer circuit 22 terminates the production of the time-up signal TU 
after the click ball 12 has become stable in the recess and therefore, 
rotation of the revolver becomes possible when the rotation start signal 
RS is again produced. 
In the above-described embodiment, correspondingly to one rotation 
indication, the revolver is rotated until the click ball is received in an 
adjacent recess and therefore, to cause the revolver to make one full 
rotation, four rotation indications are necessary in any of the case of 
clockwise rotation and the case of counter-clockwise rotation, but if, for 
example, detectors putting out different signals for the respective 
recesses are provided on the revolver and the operation device is provided 
with the function of designating a magnification of the objective lens 
corresponding to a particular recess, rotation of the revolver may be 
controlled such that a desired objective lens is selected by once 
indicating to the operation device the magnification of an objective lens 
which it is desired to insert in the observation optical path. 
Although a belt is best suited as the rotation transmitting device, the 
same function can of course be obtained even by using gears or other 
means.