Nodding scanner

A limited rotation assembly for an optical scanner. This assembly includes an input command unit and a signal generator and an electronic driver and a summing junction and a torquer connected in series. The torquer has a tachometer with a start-stop pulse feedback loop to the signal generator and with an angular velocity and position pulse feedback loop to the summing junction.

This invention relates to oscillation motors used to scan beams of light 
and more particularly to a galvanometer type scanner or nodding scanner to 
drive a mirror and more specifically to a position servomechanism used to 
drive the mirror. 
BACKGROUND OF THE INVENTION 
One such prior art scanner is described in U.S. Pat. No. 3,970,979, issued 
Jul. 20, 1976. Other related patents include U.S. Pat. Nos. 3,959,673 
issued May 25, 1976; 4,076,998 issued Feb. 28, 1978; 4,990,808 issued Feb. 
5, 1991; and 5,048,904 issued Sep. 17, 1991. 
The prior art scanner described in U.S. Pat. No. 3,976,979 includes a 
capacitive drive circuit having an output conductor, a summing junction 
having an input connected to the drive output conductor, a drive rotor 
having an elongate axis, a drive stator having a drive coil connected to 
an input of the summing junction, a sensor rotor having a sensor coil 
connected to a second input of the summing junction whereby a capacitive 
feedback loop is provided for modifying a drive signal from the summing 
junction output. 
One problem with the prior art nodding scanners is that their performance 
data is not always suitable for current sensitive applications. 
SUMMARY OF THE INVENTION 
According to the present invention, a nodding scanner assembly is comprised 
of an input command unit for providing a preprogram signal, a signal 
generator connected to the input command unit for providing output 
position pulses to an electronic driver which sends a pulse sign, a motor 
tachometer position, an oscillation sensor. The motor tachometer sensor 
comprises a motor and an oscillation tachometer unit which has a 
tachometer coil assembly and a tachometer magnet coaxially mounted on the 
rotor. The tachometer coil assembly has a first output feedback conductor 
connected to the input of the motor tachometer sensor and a second output 
conductor connector to the signal generator for providing start and stop 
pulses to the signal generator, a junction and having a second output 
conductor connected to the signal generator for providing start and stop 
pulses to the signal generator, and scanner means coaxially mounted of the 
shaft. 
By using the signals from the first and second output connectors, the 
mirror and shaft angular velocity signals can be obtained, such that the 
nodding scanner has performance characteristics which are suited to 
scanning angular position as a function of time to an accuracy which is 
not available in prior art limited rotation devices. 
A principal object of the present invention is to provide a nodding scanner 
which has performance characteristics suitable for sensitive instruments 
having scanning apparauts. 
Another object of the present invention is to provide a limited rotation 
assembly having a pulse-type drive and uses a preprogram, and which has a 
pulse type feedback loop with a pulse-type output signal to operate an 
optical scanning mirror. 
These and other objects and many of the attendant advantages of this 
invention will be readily appreciated as the same becomes better 
understood by reference to the following detailed description when 
considered in connection with the accompanying drawings in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIGS. 1, 2, and 3, an oscillation motor assembly or a limited 
rotation assembly or a nodding scanner assembly 10 is provided. Assembly 
10 has an input command unit 12, a signal generator 14 to which is 
connected to input command unit 12. An electronic driver 16, which is 
connected to signal generator 14, and a summing junction 18, which is 
connected to electronic driver 16. Assembly 10 also has a motor and 
tachometer oscillation subassembly 20, which is connected to summing 
junction 18, and which has a shaft 22 having an axis 21. The subassembly 
20 has a scan device or mirror 24, which is fixedly connected to shaft 22. 
Input command unit 12 has an output terminal 26 with a wire or conductor 
28, which is connected to an input terminal. Signal generator 14 has a 
first input terminal 30, which is connected to conductor 28. Signal 
generator 14 also has a first output terminal 32, which is connected to a 
conductor 34. Signal generator 14 also has a second input terminal 36, 
which is connected to a conductor 38, and has a second output terminal 40, 
which is connected to a conductor 42. 
Electronic driver 16 has an input terminal 44, which is connected to 
conductor 42, and has an output terminal 46, which is connected to a 
conductor 48. Summing junction 18 has a first input terminal 50, which is 
connected to conductor 48, and has a second input terminal 52 which is 
connected to a feedback conductor 54. The summing junction 18 also has an 
output terminal 56 connected to the motor tachometer of subassembly 20. 
The oscillation subassembly 20 has a first output terminal 58, which is 
connected to the conductor 54, and a second output terminal 60, which is 
connected to the conductor 38. Subassembly 20 (FIG. 3) has an oscillation 
actuator or torquer or motor unit 62, and an oscillation tachometer unit 
or alternator unit 64, and an optical encoder unit 66. 
The oscillation subassembly 20 has a casing or housing 68, and a left and a 
right bearing unit 70,72, which are supported by the casing 68, and which 
also supports the shaft 22. The subassembly 20 has an end cap 74. The 
motor unit 62 has a drive stator 76 which is mounted in the casing 68 and 
a first drive rotor 78 which is attached to the shaft 22. The right 
bearing 72 is supported by a right end wall portion 80 and the left 
bearing 70 is supported by the casing 68 at the end portion thereof. 
The tachometer 64 has a coil assembly 82, which is supported by the casing 
68 and a magnet 84 which is supported by the shaft 22. 
FIGS. 4, 5, 6 and 7 each shows and compare a test data curve of a model of 
the commercially available prior art nodding scanner assembly with a test 
data curve of a prototype of new assembly 10 according to the invention. A 
comparison of each pair of curves shows the improved performance 
characteristics of the new assembly 10. 
FIG. 4 shows the comparative linearity in a graph of percent linearity 
versus temperature. FIG. 5 shows the comparative jitter measurement in a 
graph of jitter (microsecond) versus temperature (Celsius). FIG. 6 shows 
the comparative linearity at 20 degree Celsius in a graph of percent 
linearity versus scan frequency (HZ). FIG. 7 shows the comparative jitter 
measurement at 20 degree Celsius in a graph of peak-peak jitter 
(microsecond) versus scan frequency (HZ). 
In operation, the mirror 22 reflects a laser beam in an optical scan 
apparatus (not shown). Input command unit 12 has a preprogram signal 
carried by a modulated DC wave from a power source (not shown). Assembly 
10 is similar to position servo which has an optical reflection feedback. 
The preprogram provides a selective active scan angle of about 6.0 degrees 
at a selective velocity. The preprogram also provides an overscan angle of 
about 0.5 degrees at a lower velocity. The preprogram can also be adjusted 
to suit other applications. The mirror 24 has a substantially constant 
angular velocity over its active range. The shaft 22 and the rotor 78 and 
the tachometer magnet 84 have the same angular velocity as that of the 
mirror 24. The tachometer coil 82 and the feedback conductor 54 which 
carry a velocity signal indicative of the angular velocity and exact 
angular position of the tachometer magnet 84 and of the mirror 24. This 
velocity signal is connected to summing junction 18. The encoder 66 also 
gives the exact or absolute angular position of mirror 24 at any one time, 
and also gives the home position of the mirror 24. Thus, the home and 
other positions as given by the tachometer 64, can be checked and verified 
by the encoder 66. 
Advantages of assembly 10 are indicated hereafter: 
a. Assembly 10 has a tachometer pickoff feedback loop instead of the prior 
art motor capacitive pickoff feedback loop whereby performance is 
improved. 
b. The tachometer feedback loop provides both mirror angular velocity and 
mirror angular position. 
c. Assembly 10 has an electronic driver for pulse driving of the servo 
subassembly 20. 
d. Assembly 10 provides performance data, which is substantially better 
than the prior art corresponding data. 
e. Assembly 10 has an oscillation motor unit 62 and an oscillation 
tachometer unit 64, both of which are disposed coaxially in a common 
casing for ease of alignment and manufacture. 
It should be understood that the foregoing relates to only a preferred 
embodiment of the invention, which has been by way of example only, and 
that it is intended to cover all changes and modifications of the example 
of the invention herein chosen for the purposes of the disclosure, which 
do not constitute departures from the spirit and scope of the invention.