Digital torque meter system

A system for obtaining torque and angular velocity of a load transmitting shaft (such as for example the power drive shaft in a marine propulsion system) and adapted to obtain the efficiency and power output of the shaft. The system makes use of a matched pair of optoelectronic sensors, each comprising a pair of light sources, a pair of optoelectronic pick-ups and a relatively rotating interrupter member. The pair of optoelectronic sensors permits an accurate measurement of the relative angular displacement of the relatively rotating members. The system converts a binary-type optical message into electrical pulse signals which are processed to provide readings of torque, angular velocity, power output and shaft efficiency. The optoelectronic sensors are positionally adjustable by means of set screws, and the system can be calibrated by means of self-test circuits. The optical pick-up includes a vertical array of individual optical fibers. Additionally each optical pick-up utilizes a dual set of light detectors, one above the other, with each interrupter member having an upper, smaller width portion and a lower, larger width portion with a central vertical slot therein, causing the two lights detectors to sense the following cylical, sequential conditions as the interrupter passes by: lower detector first blocked, upper detector then blocked, lower director unblocked and then reblocked (slot), upper detector unblocked, and then lower detector unblocked.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a system for measuring torque in a 
rotating shaft by means of generating and processing optically derived 
electrical signals which are a function of the torsional deflection of the 
shaft. The present invention further relates to a system for measuring 
angular velocity, power output and efficiency of a rotating shaft by means 
of generating and processing optically derived electrical signals which 
are functions of the angular velocity and torsional deflection of the 
shaft. 
2. Description of the Prior Art 
Devices for measuring torque through electronic conversion of optical 
signals generally are well known in the prior art. Attention is called to 
U.S. Pat. Nos. 3,196,675 (Buchele, et al, issued July 27, 1965); 3,495,452 
(Johnson, Jr., et al, issued Feb. 17, 1970); 3,897,766 (Pratt, Jr., et al, 
issued Aug. 5, 1975); 3,940,979 (Ward, et al, issued Mar. 2, 1976); 
3,111,028 (Lebow, issued Nov. 19, 1963); 3,950,986 (Parkinson, issued Apr. 
20, 1976); 3,625,055 (Lafourcade, issued Dec. 7, 1971); 3,596,100 
(Hollick, issued July 27, 1971); 3,604,255 (Bart, issued Sept. 14, 1971); 
3,545,265 (McIlraith, et al, issued Dec. 8, 1970); 3,960,012 (Ingram, 
issued June 1, 1976) and 4,166,383 (Lapeyre, issued Sept. 4, 1979). 
The prior art optical torque meters--Johnson, Jr., et al, Pratt, Jr., et 
al, and Buchele, et al--utilize a deflection principle in which light is 
transmitted from a light source and reflected from a shaft onto an 
optoelectronic sensor for subsequent signal processing into convenient 
form. This reflection method is hampered by errors produced by 
inconsistent turn-on times of the optoelectronic sensor caused by 
scattered light which results in decreased intensity of reflection. 
The prior art optical torque meters that utilize a direct beam pick up 
similar to that used in the present invention generally are all 
mechanically intricate and involve complex shaft attachments such as 
slotted rotating disks (Ward, et al), toothed flanges (Lebow), toothed 
wheels (Parkinson), double shafts with a rotating disk on one of them 
(Lafourcade), and light polarizing screens (Hollick). These devices are 
expensive and time-consuming to machine, require specific technical 
knowledge to install and service, cannot be placed on a shaft different 
from that on which it was initially placed without machining alterations, 
utilize complex curcuitry in which conversion of analog signals to digital 
readouts is necessary, and suffer a scattered light problem similar to the 
deflective torquemeters mentioned above. 
Systems for measuring power, angular velocity and shaft efficiency 
generally are also known. Such devices use a variety of relatively complex 
methods--e.g. a proximity pick-up located adjacent to gears mounted on the 
shaft and generating alternating current waves (Bart), magnetic sensors 
(McIlraith, et al), and assemblies to separately generate signals 
proportional to torque and angular velocity (Ingram). In addition to the 
necessity of analog to digital signal conversion and the relative 
complexity of the measurement process, none of the prior art devices use 
optical signal transmission as does the present invention. 
SUMMARY DISCUSSION OF THE INVENTION 
It is a primary object of the present invention to provide a novel 
modification of and improvements upon the optical torquemeter systems 
disclosed in the prior art. Specifically the present invention seeks: 
(1) to provide an optical torquemeter that eliminates the necessity for 
analog to digital conversion; 
(2) to construct a torque, angular velocity, horsepower, and efficiency 
monitoring system capable, at least in part, of integrated circuit 
fabrication; 
(3) to provide a system capable of being calibrated either with the shaft 
motionless or in motion; and 
(4) to construct a system that provides consistent and accurate turn-on of 
the optoelectronic pick-ups at appropriate times. 
The present invention provides numerous improvements and advantages over 
the prior art in that all computations are electronic, direct and 
automatic, that high precision readings are facilitated, that attachment 
to a shaft and interchange of shafts is simplified, that indications of 
torque, horsepower, angular velocity and shaft efficiency are provided, 
that all read-out measurements are extremely rapid, and that the overall 
system is compact, light weight and economical to manufacture. 
The present invention utilizes two optoelectronic sensors mounted on a 
bearing housing by means of an adjusting plate. Each sensor includes a 
pair of light sources and a corresponding pair of optoelectronic pick-ups. 
Each sensor is positioned so that an interruptor plate mounted on a shaft 
will be interposed between the light sources and the corresponding 
pick-ups, blocking the light transmission, during each revolution of the 
shaft. 
Preferably each optoelectronic sensor includes a primary set of a light 
source and a light detector and a secondary set of a light source and a 
light detector positioned one above the other in radial array, with the 
interrupter having at least two, radially spaced portions or sections, a 
lower portion in which a vertical radial, slot is centrally located and an 
upper portion having a lesser width, with the two interrupter sections 
creating a different pattern or timed sequence of light blocking and light 
passing or unblocking with respect to the two sets of light sources and 
detectors. The interrupter of the secondary set is used to electrically 
control the out-putting of the primary detector so that its output is only 
seen or used when the interrupter is passing by. Also, the primary light 
source is preferably formed by a vertical, radial array of fiber optics 
producing a thin, straight line light source similar in size and 
configuration to the slot in the interrupter, which combination produces a 
particularly accurate, precise timed indication of the passage of the 
interrupter. 
Each optoelectronic sensor is identical except for the mounting location of 
each along the shaft. Sensors can be positioned apart any convenient 
distance along the shaft. A correction factor for distance separation can 
be set into the microprocessor. 
The microprocessor monitors the sequence of interruption of the light 
source and records the time difference between interruptions from the two 
optoelectronic sensors. Several time difference recordings are averaged 
and the amount of twist of the shaft is calculated using appropriate 
constants describing the modules of rigidity, shaft diameter and shaft 
construction. The detected amount of twist, which is extremely small, that 
occurs in the shaft is directly proportional to the torque in a shaft and 
follows in a linear pattern over the range of torque applied for 
propulsion. In other words, the maximum torque does not normally exceed 
the elastic limits of the shaft. 
Although the torque in a rotating member is along an arc, the amount of 
twist that takes place is so small that no measurable error is introduced 
when twist or flexure is evaluated as a linear displacement along a chord 
subtending this radial arc. 
The modulus of rigidity in any particular shaft is readily ascertainable by 
known methods using specific weights to load the shaft and comparing 
actual twisting with modulus of rigidity tables provided by the shaft 
manufacturer and based upon the alloyed steel and type of heat treatment 
involved. Thereafter, by calibrating the microprocessor and the sensors, 
the output signal provided by the same can be made directly proportional 
to and representative of actual shaft torque. 
Since, as described above, the modulus of rigidity of any particular shaft 
may be readily computed, it is therefore only necessary to measure the 
magnitude of the twist in the shaft over a specific distance, which 
measurement indicates the torque of the shaft under load. 
Sensors are tested and calibrated during manufacture and are matched so as 
to be interchangeable. Interruptors are precisely machined to make them 
identical. Sensors are mounted on a bearing housing by means of a mounting 
bracket which is attached to the bearing housing with epoxy or with bolts. 
Each mounting bracket contains an adjusting plate to which an 
optoelectronic sensor is attached. The adjusting plate and with it the 
attached sensor can be vertically or horizontally repositioned by means of 
set screws. Calibration of each sensor is accomplished by adjusting the 
set screws so that the fiber optics are in alignment with the slot on the 
interruptor. When alignment is achieved, a self calibration display from 
the microprocessor is activated. To avoid offset error, calibration should 
be performed when no torque is present on the shaft. 
Angular velocity of the shaft is measured by evaluating the frequency of 
interruption of a light source on one of the optoelectronic sensors. Such 
evaluation directly determines shaft speed in revolutions per minute 
(RPM). A shaft horsepower (SHP) determination is derived from RPM and 
torque measurements by the following formula: 
##EQU1## 
Efficiency of power is obtained by a simple calculation which takes a ratio 
of shaft horsepower to power input. The calculation is performed in the 
microprocessor. 
The present invention thus provides an easily utilized and highly accurate 
optoelectronic means for obtaining torque, horsepower, velocity and 
efficiency measurements which heretofore were obtained by complex and 
marginally reliable devices, subject to the inaccuracies previously 
discussed with respect to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a general, exemplary propeller shaft assembly 10 
comprising a shaft 11, a propeller 13 and an engine 14. In the preferred 
embodiment of the present invention, two optoelectronic sensors 20A and 
20B are mounted one on either side of a bearing 12 by means of adjusting 
plates 40A and 40B, the frame of which is attached to the bearing 12 by 
means of for example epoxy or by bolts. One optoelectronic sensor 20A is 
mounted on the propeller side of the bearing 12, and the other 
optoelectronic sensor 20B is mounted on the engine side of the bearing 12. 
Two interruptors 50A and 50B are mounted on the shaft 11 by means of 
mounting brackets 60A and 60B attached to the shaft 11, one interruptor 
being positioned on each side to the bearing 12 so that the rotation of 
the shaft 11 will cause the interruptors 50A and 50B periodically and 
cyclically to be interposed between the light sources, primarily 22A and 
22B and secondarily 23A and 23B, and the optical pick-ups, primarily 25A 
and 25B, and secondarily 24A and 24B of the optoelectronic sensors 20A and 
20B, respectively. 
The two optoelectronic sensors 20A and 20B can also for example be mounted 
on the shaft 11 by means of separate bearings and can be spaced apart at 
greater or lesser distances as desired. 
FIG. 2 more closely details the structure of each optoelectronic sensor 20A 
and 20B. Each sensor comprises a sensor chassis 21 bolted to an adjusting 
plate 40A and 40B. To the sensor chassis 21 are attached one secondary 
light source 23, one primary light source 22 (each source comprising a 
conventional light emitter), one secondary optical pick-up 24 comprising a 
photodetector, one primary optical pick-up 25 consisting of a plurality of 
vertically arranged optical fibers, of which a front view is shown in FIG. 
4, an optical cable 26 which leads from the primary optical pick-up 25 to 
an optical housing 27 mounted on a circuit board 28 which is separated 
from the sensor chassis 21 by means of spacers 29. 
The secondary light source 23 is positioned radially above the primary 
light source 22 and both sources are positioned so that the interruptors 
50 will sequentially block and unblock the light from each source from 
impinging on its respective optical pick-up, as discussed more fully 
below. 
Various appropriate electronic modules 30, including the necessary 
circuitry for the system, are mounted within the housing for the 
optoelectronic sensors 20A and 20B. Typical exemplary circuitry is 
illustrated in FIGS. 5 and 6, discussed in greater detail below. A 
suitable power source (not illustrated) is of course included for the 
system. 
FIG. 3 illustrates the interruptor 50 which comprises a stainless steel 
plate that is slotted in the middle. The slot 53 preferrably is machined 
to the exact width of the primary optical pick-up 25, of which a front 
view of the fiber optics 25 mounted vertically in the detector chassis 21 
is shown in FIG. 4. 
Each interruptor plate 50 is a tri-level, thin plate. A representative 
gauge is between one-sixteenth and one-sixty-fourth inches. It is noted 
that the gap in the optical sensors 20A and 20B through which the 
interruptor plate 50 passes are as small as possible, for example 
one-eight of an inch, and generally the mounting hardware is not included 
within the gap as is shown in FIG. 2. The first level 55 is a rectangular 
mounting base with slotted bolt holes 70 for adjustably attaching the 
interruptor plate 50 onto a mounting bracket 60 which is mounted on the 
shaft 11 (note FIG. 8). The second level 56 is rectangular with a 
centered, vertical slot 53. The third level 57 is a solid, lesser width 
rectangle centered over the second level. 
It should be noted that the foregoing breakdown into levels is for 
convenience of description and does not indicate separate pieces. The 
interruptor plate 50 can be and preferrably is cut from a single piece of 
material. The preferred material for the interruptor plate 50 is stainless 
steel, although other metals and even plastics can be used. Representative 
dimensions associated with the interruptor plate 50 are as follows: 
______________________________________ 
(a) Mounting base level 
2 to 4 inches in width; 
1/4 to 3/8 inches in height; 
(b) Second level 2 to 4 inches in width; 
3/8 to 3/4 inches in height; 
slot 1/16 to 1/64 inches in width; 
3/8 to 3/4 inches in height; 
(c) third level 1 to 2 inches in width; 
3/8 to 3/4 inches in height; 
______________________________________ 
All of these dimensions are merely representative and the interruptor plate 
50 can be enlarged or reduced in size without significantly affecting the 
performance of the digital torque meter. 
The interruptor plates 50 rotate with the shaft 11. Each plate 50 is 
positioned so that each revolution of the shaft 11 causes the plates 50 to 
interrupt the light beams which would otherwise impinge on the 
optoelectronic pick-ups 20A, 20B. The light sources of each optoelectronic 
sensor 20A, 20B are arranged so that one source 23, called the secondary 
source, is positioned radially above another source 22, called the primary 
source. 
During most of a revolution of the shaft 11 the interruptor plate 50 does 
not block the source lights 22, 23 from impinging on the pick-ups. 
However, as the plate 50 rotates into position, the leading edge of the 
plate 50 blocks the light from the primary light source 22. The plate and 
the primary light source 22 are arranged so that this blockage occurs at 
the second level 56 of the interruptor plate 50. (The third level 57 has 
not yet moved into position to block the light from the secondary source 
23.) As the interruptor plate 50 rotates with the shaft 11, the light 
sources 22, 23 are alternately blocked and unblocked. The sequence of 
interruption referenced to interruption of the primary and secondary light 
sources 22, 23 by the interruptor plate 50 is as follows: 
______________________________________ 
LIGHT SOURCE 
Primary(22) Secondary(23) 
______________________________________ 
(a) blocked unblocked 
(b) blocked blocked 
(c) unblocked blocked 
(d) blocked blocked 
(e) blocked unblocked 
(f) unblocked unblocked 
______________________________________ 
The above six step sequence is repeated once every revolution. 
Each primary optoelectronic pick-up preferrably comprises a vertical 
arrangement or array of thin optical fibers 25, one positioned above the 
other. The optical fibers 25 are connected by means of an optical cable 26 
to an optical housing 27 which contains a photo sensor relatively 
insensitive to extraneous light. Each secondary optoelectronic pick-up 
comprises a photo sensor 24 which gates the signals from the primary light 
source 22 into a microprocessor. Signals pass to the microprocessor only 
when the interruptor slot 53 aligns with the primary optoelectronic 
pick-up 25, while at the same time the light from secondary source 23 to 
the secondary pick-up 24 is blocked by plate section or portion 57. This 
condition occurs once during each revolution. 
FIG. 5 provides a block diagram of exemplary signal processing circuitry. 
The electronic signals derived from the optoelectronic sensors 20A and 20B 
are processed in a time difference recorder 61 to produce a signal 
proportional to the torsional deflection of the shaft 11. Many such 
signals are averaged in a time difference averager 62, and the resultant 
averaged signal is processed in a torque processor circuit 63 to produce a 
signal proportional to the torque developed in the shaft. The signal from 
the torque processor circuit 63 is displayed in convenient form by means 
of a torque readout circuit 64. The signal derived from an optoelectronic 
sensor is processed in an RPM counter circuit 65, and a resultant signal 
proportional to angular velocity is displayed in convenient form by means 
of an RPM readout circuit 67. Signals proportional to shaft horsepower are 
developed in the horsepower processor circuits 66, from signals derived 
from the torque processor circuit 63 and the RPM counter circuit 65. The 
signal produced in the horsepower processor circuit 66 is displayed in 
convenient form by means of a horsepower readout circuit 68. 
FIG. 6 shows a schematic diagram of exemplary circuitry used to derive a 
signal to be processed further by the processor and counter circuits. The 
secondary phototransitor 24 converts an impinging optical signal from the 
secondary light source 23 into an electronic signal. The signal is 
inverted in an inverting amplifier 32 and is inputted into an "AND" gate 
34. Similarly, the primary phototransitor 27 converts an impinging optical 
signal from the primary light source 22 into an electronic signal, which 
is amplified by an amplifier 33 and is inputted into the "AND" gate 34. 
The logic of the circuitry provides a signal that is amenable for further 
digital processing. 
FIG. 7 more clearly details the structures of the adjusting plate 40. The 
sensor chassis 21 (see FIG. 2) is installed inside the milled area 44. The 
adjusting plates 40 all for example epoxied or bolted to the bearing 12. 
The mounting holes 43 are machined for example for quarter inch bolts for 
this purpose. The horizontal, adjusting Allen screws 41 and the vertical, 
adjusting Allen screws 42 are used for proper positioning of the sensor 
chassis 21 inside the adjusting plate 40 prior to "permanent" mounting. 
FIG. 8 more clearly details the mounting bracket 60 which mounts the 
interruptor 50 onto the propeller shaft 11. The lower portion of the 
mounting brackets 60 is machined to fit flush around the shaft 11. 
Permanent fastening of the mounting brackets 60 to the shaft 11 is 
accomplished for example either with the use of epoxy or by bolting. The 
interruptor 50 is bolted to the upper portion of the mounting bracket 60. 
Its position relative to the position of the corresponding sensor 20 can 
be adjusted by using the slotted holes 70 where the interruptor 50 is 
bolted to the mounting bracket 60. The mounting bracket 60A can for 
example be a quarter inch thick. 
Because of the many varying embodiments that may be made within the scope 
of the inventive concept herein taught, and because many modifications may 
be made in the embodiment herein detailed in accordance with the 
disclosure requirements of the law, it is to be understood that the 
details herein are to be interpreted as illustrative, and not in a 
limiting sense.