Redundant indicator for detecting neutral position of joystick member

An electronic controller having a joystick member, the controller utilizing one or more electrical output circuits characterized by parameters which vary in accordance with the displacement of the joystick member from a "neutral" position in X-axis and Y-axis directions, to control positions on opposite sides of the "neutral" position. The joystick member has a light-reflecting area which traverses a predetermined field of travel as the member is moved between its various positions. A light emitter-sensor circuit including a light source and a light sensor is disposed in the field of travel of the light-reflecting-area of the joystick member. The emitter-sensor circuit generates an electrical signal from a reflected beam of light which is emitted from the light source and is reflected from the reflecting area of the joystick member and onto the light sensor, only when the joystick member is at, or very close to its "neutral" position. An especially accurate, back-up or redundant-type indication or confirmation of the "neutral" positioning of the joystick member can thereby be achieved at minimal cost, for safety and/or reliability of operation.

NO CROSS REFERENCES TO RELATED APPLICATIONS 
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSORED 
RESEARCH AND DEVELOPMENT. 
Research and development of the present invention and application have not 
been Federally-sponsored, and no rights are given under any Federal 
program. 
BACKGROUND OF THE INVENTION 
FIELD OF THE INVENTION 
This invention relates generally to joystick controllers, and more 
particularly to devices for accurately detecting specific ranges of 
movement of the actuator arms of such controllers. 
More particularly, the present invention relates to improvements in 
joysticks. An example of a commercial joystick is shown in applicant's 
U.S. Pat. No. 4,825,157 issued Apr. 25, 1989, entitled HALL-EFFECT 
CONTROLLER. 
DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR 
.sctn..sctn.1.97-1.99 
The entire disclosure of U.S. Pat. No. 4,825,157 above identified is 
incorporated into the present application, by specific reference. One of 
the problems inherent in all prior joysticks was that of accurately 
detecting the center or "neutral" position of the actuator arm or control 
member. In practice, the usual X-axis and Y-axis outputs that are utilized 
in conventional joystick constructions have been heavily relied upon for 
adequate accuracy and repeatability, as well as freedom from inadvertent 
failure. 
Under certain applications and in actual practice, however, it has been 
found that the reliability is, in many cases, inadequate. With some 
systems, a temporary loss of signal such as from an intermittent or noisy 
potentiometer, may prove to be of only minimal concern. 
With other systems, however, such as applications involving control of 
large or heavy equipment, and where a joystick failure can result in 
injury to personnel and/or damage to factory equipment, there has arisen a 
need to verify or otherwise check, in a reliable manner, the joystick 
operation, and more particularly to be able to confirm when the actuator 
member of a joystick was truly disposed at a physical center or "neutral" 
position. 
Moreover, attempts to solve the problem of providing an independent check 
or back-up reading of such a "neutral" position have either been 
unsuccessful, or alternately not workable from a commercial or practical 
standpoint. 
SUMMARY OF THE INVENTION 
Accordingly it is an object of the present invention to provide a novel and 
improved "neutral" position indicator for a joystick controller, the 
position indicator being of a "confirmation" or "redundant" type, that is, 
one which provides an independently obtained reading of the "neutral" 
position of the actuator member of a joystick, and one which utilizes 
components that are completely separate and distinct from the existing 
X-axis and Y-axis position sensors and their associated circuitry, as 
normally relied upon in conventional joystick constructions. 
A related object of the invention is to provide an improved "neutral" 
position indicator as above set forth, which is extremely simple in 
operation, and which can be supplied as original equipment in a joystick 
assembly, or alternately supplied as an add-on or accessory, for an 
existing system. 
Still another object of the invention is to provide an improved neutral 
position indicator of the type noted above, which, by virtue of its 
simplicity, has an extremely high degree of reliability, thereby virtually 
eliminating unexpected catastrophic type failures. The high reliability is 
largely a consequence of the provision of two separate and distinct, 
independent sets of sensing controls for the actuator member of the 
joystick, one set serving as the redundant-type indicator for providing 
confirmation-type neutral position readings. 
Yet another object of the invention is to provide an improved neutral 
position indicator as above characterized, which utilizes few components 
in a simple configuration, thereby being inexpensive to produce, and thus 
lending itself to widespread commercial adaptability without materially 
increasing the overall cost of a joystick. 
A still further object of the invention is to provide an improved neutral 
position indicator of the kind indicated, wherein precise readings 
confirming the neutral position of the actuator member of a joystick can 
be obtained quickly, and with virtually no uncertainty, thereby giving 
rise to exceptional reliability and increased safety. There are thus 
minimized potential hazards to operating personnel and/or factory 
equipment. 
Still another object of the invention is to provide an improved method for 
installing a neutral position indicator in a joystick controller, which 
method is readily carried out and which utilizes a minimum of separate 
operations; the method employs simple electronic components that are 
readily available in the marketplace. 
The above objects are accomplished by a neutral position indicator for a 
joystick-type controller, comprising in combination a movable control 
member having control positions which are reached from a given neutral 
position, and emitter-sensor means comprising a light source and a light 
sensor. The control member has a light-reflecting area thereon which 
traverses a predetermined field of travel as the member is moved between 
its various positions. The emitter-sensor means is disposed in the field 
of travel of the light-reflecting area of the control member and is 
adapted to produce an electrical signal from a reflected beam of light 
which is generated by and emitted from the light source, and is reflected 
from the reflecting area of the control member and onto the light sensor 
when the control member is in its neutral position. 
The objects are further accomplished by control means comprising, in 
combination a joystick type control device having a joystick member, and 
having one or more electrical output means characterized by parameters 
which vary in accordance with the displacement of the joystick member from 
a neutral position in X-axis and Y-axis directions, toward control 
positions therealong. The joystick member has a light-reflecting area 
which traverses a predetermined field of travel as the member is moved 
along its control positions. There are provided emitter-sensor means 
comprising a light source and a light sensor, both the source and the 
sensor being disposed in the field of travel of the light-reflecting area 
of the joystick member and being adapted to produce an electrical signal 
from a reflected beam of light. The beam is initiated at and emitted from 
the the light source and is reflected from the reflecting area of the 
joystick member and onto the light sensor only when the control member is 
in its neutral position. 
The objects are still further accomplished by the provision of a novel 
method for measuring or sensing the neutral position of a joystick 
controller's actuator member. In the practice of the method, the joystick 
controller comprises a movable joystick actuator member having an end 
portion, and comprising electrical circuit means for measuring the angular 
displacement of the joystick member from a central, neutral position and 
in both X-axis and Y-axis directions. These directions lie in a plane that 
is substantially perpendicular to the joystick member when the latter is 
disposed in its neutral position. The method of the invention in effect 
provides a redundant indication, via a separate and distinct signal from 
that of the electrical circuit measuring means, to detect movement of the 
joystick member from its neutral position, and comprises the steps of 
placing a light source and a light sensor in juxtaposition with one 
another, in a zone corresponding to the location of the end portion of the 
joystick member when it is in its neutral or central position; providing a 
light-reflective surface on the end portion of the joystick member; 
energizing the light source so as to emit a beam of light toward the zone; 
and measuring the output of the light sensor to determine if light from 
the light source is striking the reflective surface, so as to be reflected 
therefrom and be beamed back toward the light sensor. Such a reflected 
beam thus indicates the presence of the reflective surface in the zone, 
which corresponds to the joystick member being disposed in its neutral 
position. The measurement so obtained is separate and distinct from that 
of the electrical circuit measuring means of the joystick controller, 
thereby providing an independent and redundant indication of the position 
of the joystick member when it is disposed in its neutral position. 
Significantly improved reliability in the determination of the neutral 
position of the joystick member is realized as a consequence of this 
redundant or "confirmation" reading of the neutral position. 
The objects are further accomplished by the provision of a novel method for 
measuring or sensing the neutral position of a joystick controller 
actuator member. The joystick controller comprises a base and an elongate 
movable member pivotally carried by the base. The elongate movable member 
has an inner end portion and is movable on the base between a central, 
neutral position, and radially-extending angularly displaced positions. In 
particular, the method is intended generally to detect, in a redundant 
manner or fashion, movement of the joystick member away from its neutral 
position, and comprises the steps of placing a radiation source and an 
electro-responsive radiation sensor in juxtaposition with one another in 
the base at a zone therein adjacent to the location of the end portion of 
the movable member when it is in its central or "neutral" position; the 
method further comprises the steps of establishing a radiation-reflective 
surface on the end portion of the member; energizing the radiation source 
so as to emit a beam of radiation at the zone; and measuring the response 
of the electro-responsive radiation sensor to determine if radiation from 
the radiation source is striking the radiation-reflective surface and 
being reflected therefrom, and thereafter being beamed back toward the 
radiation-sensor. The method thus indicates the presence of the reflective 
surface in the center of the zone, this corresponding to the movable 
member being disposed in its neutral position. 
Other features and advantages will hereinafter appear.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the FIG. 1, there is provided a joystick or joystick-type 
controller including an electronic circuit which produces output voltages 
that are indicative of the X-axis and Y-axis positions of the joystick 
handle. 
In FIGS. 1 and 2 the joystick is generally designated by the numeral 10, 
comprising a housing 12 having a base 14, a cover 16 for the base 14, and 
a bearing plate 18 for mounting a handle or joystick actuator member 20. 
The cover 16 and bearing plate 18 each have a central aperture which forms 
part of a pivot socket 22. The handle 20 has a manually-engageable knob 
23, return spring 24, and a ball 26 which is held captive in the socket 
22. The spring 24 maintains the handle 20 in a normal vertical or 
"neutral" position with respect to the base 14. 
By way of example, a joystick controller of the type utilizing Hall-effect 
sensors as position indicators will be described hereinbelow, although the 
present invention is applicable to any type of joystick controller. 
Referring again to FIG. 1, there is mounted on the base 14 an electrical 
energizing coil 28 of doughnut-like configuration, having a central 
opening 30 and electrical leads 32, 34. The handle of actuator member 20 
has a magnetic core 36 which, in the illustrated construction, extends 
through the central opening 30 of the coil 28. The core 36 can be 
constituted of any suitable magnetic material, such as iron or steel, 
alloys thereof, ferrite, or equivalents. 
Also, there are provided four proximity sensors 38, 40, 42, and 44 
adjustably mounted in the base 14, in positions such that they are 
subjected to the magnetic field provided by the energizing coil 28 and the 
magnetic core 36. As noted above, the proximity sensors, can take the form 
of Hall-effect devices that are magnetic-responsive. Three sensors 38, 40 
and 42 are shown in FIG. 1, whereas all four sensors 38, 40, 42 and 44 are 
shown in FIGS. 2 and 3. In the latter figure, the triple leads of the 
sensors 38, 40, 42, and 44 are labelled 46, 48, and 50; 52, 54, and 56; 
58, 60, and 62; and 64, 66, and 68, respectively. These numerical 
designations have been omitted from FIG. 1, for clarity. 
Again, as an example, a typical Hall-effect sensor 38 is shown in FIG. 4. 
The sensors 40, 42 and 44 are identical to each other, and to the sensor 
38. The sensors 38, 40, 42, and 44 are in the form of integrated circuit 
packages each having three leads, such as those labelled 46, 48, and 50. 
The integrated circuit packages each contain a Hall-effect semiconductor 
70 and a follower stage or amplifier 72 which boosts the signal from the 
Hall-effect semiconductor 70. Biasing resistors 74 and 76 are associated 
with the amplifier 72. The integrated circuit packages are commercially 
available in the trade, being known as Hall Sensor Integrated Circuits, or 
Hall Sensor ICs, such as manufactured by Texas Instruments, under the part 
number TI 173. 
In the present instance, the Hall-effect sensors provide a predetermined 
output voltage, typically +6 volts d.c. with superimposed a.c., when the 
actuator member 20 is in its central, or "null" position. This is also 
referred to as a "neutral" position. The a.c. component of the output 
voltage varies with changes in magnetic flux, as determined by the 
relative positioning of the actuator member 20 with respect to the 
sensors. 
The actuator or control member 20 can pivot within limits, such that the 
lower end thereof moves laterally within a predetermined zone of travel, 
indicated in dotted outline at 21 in FIG. 7. Between these limits lies an 
infinite number of control positions, as can be readily understood. 
The magnetic flux generated in the energizing coil 28 is alternating or 
fluctuating. Correspondingly the magnetic flux sensed by each of the four 
Hall-effect sensors 38, 40, 42 and 44 is fluctuating, and as noted above 
the output of each Hall-effect sensor is typically characterized by a 
particular d.c. level with superimposed a.c. component. 
In the electronic circuit 77 illustrated in FIG. 3, all d.c. components of 
the output signals of the Hall-effect sensors 38, 40, 42, and 44, namely 
those d.c. levels on lines 50, 56, 62, and 68, respectively are completely 
blocked by series coupling capacitors 78, 80, 82, and 84, respectively. 
The series capacitors isolate those portions of the electronic circuit 77 
which follow the capacitors 78, 80, 82, and 84, from the effects of d.c. 
magnetic fields sensed by the Hall-effect sensors 38, 40, 42, and 44, 
respectively. Such d.c. components would otherwise interfere with readings 
of the position of the actuator member 20. Even the magnetic field of the 
earth, which for all practical purposes can be considered relatively 
stationary, or d.c. over the short term, is sufficiently strong to alter 
the d.c. components of the outputs of the Hall-effect sensors 38, 40, 42, 
and 44. 
Further, the electronic circuit 77 processes the a.c. components of the 
outputs of the Hall-effect sensors 38, 40, 42, and 44, and converts them 
to a pair of d.c. voltages, one of the pair of voltages corresponding to 
the position of the actuator member 20 in an X-axis direction, and the 
other one of the pair of voltages corresponding to the position of the 
actuator member 20 in a Y-axis direction. These voltages appear on output 
terminals 86, 88 respectively. 
Referring again particularly to the schematic diagram of FIG. 3, the 
various components of the circuit 77 are supplied with +12 volts d.c., as 
indicated by the terminals labelled "+12". These terminals are all 
connected together by a common line (not shown), hereinafter referred to 
as a positive supply line. 
The energizing coil 28 is connected between the line supplying +12 volts 
and the collector 90 of a switching transistor 92. A protective diode 94 
is connected across the coil 28, to suppress induced voltages which would 
otherwise be present when the coil 28 was excited by a pulsed voltage. The 
base 96 of transistor 92 has a biasing resistor 98. 
Amplifier 100 is connected as a square wave generator, and produces pulses 
on line 102, at a frequency of typically 1000 Hz. These are in turn 
applied to the base 96 of transistor 92, through resistor 104. Associated 
with the square wave generator are resistors 106, 108,110, and 112, and 
capacitor 114. The transistor 92 thus switches on and off at a rate of 
1000 Hz, which, via transistor 92, applies a 1000 Hz signal to the 
energizing coil 28. Current through the coil is approximately 20 mA. a.c., 
and the applied signal is actually in the form of a symmetrical square 
wave. 
A reference voltage of typically +6.0 volts d.c. is provided by a second 
amplifier 116; the voltage applied to the noninverting input is set by 
resistors 118 and 120. The amplifier 116 has 100% negative feedback, and 
its function is to provide a steady, regulated voltage on line 122; the 
line 122 thus constitutes a low-impedance, constant voltage d.c. supply 
line which provides +6 volts d.c. to the inputs of various other 
amplifiers, as will be described below. Capacitors 124,126 and 128 are 
filters, for reducing noise. 
As shown in FIG. 3, two leads of each of the Hall-effect sensors are 
connected to the positive supply line and to ground, respectively. The 
third lead of each device is the output, these leads being labelled 50, 
56, 62, and 68 respectively. As noted above, connected to each output is a 
series coupling capacitor 78, 80, 82, and 84, respectively which 
effectively blocks all d.c. components in the output signals. In series 
with capacitors are resistors 130,132, 134, and 136 respectively, which in 
turn are connected respectively to the inverting input of a first 
amplifier 138, the non-inverting input thereof, the inverting input of a 
second amplifier 140, and the non-inverting input thereof. The voltage 
gain of amplifier 138 is determined by resistors 130 and 142, whereas the 
gain of amplifier 140 is set by resistors 134 and 144. Bias for the 
non-inverting input of amplifier 138 is obtained through resistor 146, 
which extends to the reference voltage line, +6 volts; similarly, bias for 
the non-inverting input of amplifier 140 is obtained through resistor 148. 
Capacitor 150 constitutes a by-pass, to limit noise on the supply line. 
The outputs 152, 154 of amplifiers 138, 140 respectively are fed to two 
input terminals 3 and 6 of a quad analog switch 156. Only two of the four 
switches (shown dotted) in this device are employed in the present 
circuit. Capacitor 158 reduces noise on the supply line. The quad analog 
switch 156 has terminals labelled 1, 4, 5, 8, 9, and 16, as shown. The 
trigger input terminals 1 and 8 are fed from a divider string consisting 
of resistors 160 and 162. A Zener diode 164 provides protection against 
overvoltage, for the trigger input terminals 1 and 8 of the quad analog 
switch 156. 
Resistor 160 in turn extends to a coupling capacitor 166, which is 
connected to the output 102 of the square wave generator 100. Capacitor 
166 and resistors 160 and 162 thus constitute a differentiating circuit 
which converts the square wave at the output 102 of the generator 100 to 
short pulses, each typically having a length of 50 microseconds. These 
pulses are applied at a frequency, or pulse repetition rate of 1000 Hz, to 
the trigger input terminals 1 and 8 of the quad analog switch 156. The 
arrangement is such that the quad analog switch 156 conducts (i.e. 
connects input terminal 3 to output terminal 2, and connects input 
terminal 6 to output terminal 7) during the peak of the fluctuating signal 
at the outputs 152 and 154 of amplifiers 138 and 140, respectively; with 
the conductions thus provided by the quad analog switch 156 during such 
peaks, capacitors 168 and 170, connected to the two output terminals 2 and 
7 respectively of the quad analog switch 156, charge up to the peak values 
of the waves at the outputs of the amplifiers 138 and 140 respectively. 
The quad analog switch 156 and the capacitors 168 and 170 thus function as 
peak detectors, or sample and hold circuits. The respective voltages 
across capacitors 168 and 170 are essentially d.c. 
In effect, the quad analog switch 156 and capacitors 168, 170 constitute 
rectifying circuits, which rectify the a.c. component of the waves at the 
output terminals 152 and 154 of amplifiers 138 and 140, respectively. The 
rectified waves are filtered by the capacitors 168 and 170, respectively. 
The arrangement reduces the effect of stray a.c. magnetic fields on the 
readings of the position of the actuator member 20. This is accomplished 
by triggering the analog switch 156 in synchronism with, or in phase with 
the a.c. components of the outputs of the Hall-effect sensors. The 
triggering of the analog switch occurs at a given phase point on the 
outputs of the Hall-effect sensors, and at the same point during each 
cycle. Thus, any stray a.c. field which does not have the exact same 
frequency and phase relationship with the 1000 Hz output from the square 
wave generator 100 will have difficulty in passing through the quad switch 
and will thus not adversely affect the d.c. levels on the capacitors 168 
and 170. These d.c. levels ultimately determine the d.c. voltage readings 
on output terminals 86 and 88. 
The d.c. voltages on terminals 2 and 7 are fed respectively into voltage 
follower amplifiers 172 and 174, respectively, each having a voltage gain 
of one. The outputs of these amplifiers 172 and 174, respectively are in 
turn connected, through variable resistors 176 and 178 respectively, to 
the inputs of additional, variable gain amplifiers 180 and 182, 
respectively; the gain of amplifier 180 is determined by resistors 184 and 
176, whereas that of amplifier 182 is determined by resistors 186 and 178. 
The non-inverting input of each amplifier 180,182 is connected to the 
reference line 122, which, as noted above, is maintained at +6 volts d.c. 
Setting the gains of amplifiers 180 and 182 is effected by adjusting the 
variable resistors 176 and 178, respectively. 
With the above arrangement, there are provided electrical parameters 
comprising a pair of voltages at the output terminals 86 and 88, 
respectively of amplifiers 180 and 182. That appearing on the output 
terminal 86 of amplifier 180 is indicative of displacement of the actuator 
member 20 of FIG. 1 in the X-axis direction (FIG. 2), whereas that 
appearing on the output terminal 88 of amplifier 182 is indicative of the 
displacement of the actuator member 20 in the Y-axis direction. 
Thus, the present arrangement achieves the desired result, namely obtaining 
two d.c. voltages on terminals 86 and 88 respectively, that are indicative 
of the X and Y positions, with high accuracy and freedom from error due to 
stray d.c. magnetic fields. Also eliminated are other errors as might 
arise from temperature drifts, aging of the components, or other forms of 
incidental interference. 
This result was not previously obtainable with prior controllers where a 
bar magnet was carried on an actuator member, and wherein Hall-effect 
sensors were employed to sense the variation in the d.c. magnetic field as 
the member was moved. In such a situation, stray d.c. fields upset the 
readings. In addition, over time, the flux provided by the bar magnet 
weakened, also distorting the readings. 
The a.c. signal provided by the energizing coil 28 is relatively constant 
with time; temperature variations appear as common-mode changes in the 
a.c. signal, and are balanced out by the provision of the differential 
amplifiers 138 and 140. All d.c. components in the outputs of the 
Hall-effect sensors are completely blocked by the series capacitors 78, 
80, 82, and 84. Thus, stray d.c. magnetic fields have absolutely no effect 
on the voltages applied to the first amplifiers 138 and 140. The voltages 
on the non-inverting inputs of amplifiers 138 and 140 are characterized by 
a d.c. level determined by the d.c. voltage on the reference line 122, 
with a superimposed a.c. signal which depends on the amplitude of the 
signal received from the respective Hall-effect sensor 40, 44. The 
voltages on the two inverting inputs of amplifiers 138 and 140 are also 
characterized by a d.c. level with a superimposed a.c. signal received 
from the respective Hall-effect sensor 38, 42. 
Also, initial adjustments in the physical positions of the Hall-effect 
sensors can be made in order to compensate for slight offsets which may 
occur. The adjustments can be made by frictionally mounting the 
Hall-effect sensors 38, 40, 42, and 44 on four small brackets indicated 
188 mounted on the inner surface of the housing 12, and which permit 
adjusting-type movements of any or all of the Hall-effect sensors 38, 40, 
42, and 44 toward or away from the core 36; the initial adjustment is made 
while the latter is disposed at its center or neutral position, by 
observing the voltages on terminals 86 and 88 respectively. Following 
adjustment, the sensors can be cemented in position. 
Excellent linearity can be attained with the disclosed system. In actual 
tests performed on working models, linearity between the movement of the 
actuator member 20 and the variation in output voltages on lines 86 and 88 
from amplifiers 180 and 182, respectively, can be held to 5% or better. 
Amplifiers 138, 140, 180, and 182, while shown as separate, can be 
contained in a single package, known as a quad amplifier; a typical 
component type would be an LM 324, manufactured by National Semiconductor. 
Similarly, the four amplifiers 100, 116, 172, and 174 can be of this same 
type, contained in a single package. In such a case, the capacitor 150 
provides filtering for the power lead for all four amplifiers 138, 
140,180, and 182, while the capacitor 124 provides filtering for the power 
lead for the four amplifiers 100,116, 172, and 174. 
The quad analog switch can be a type LF 13331, also manufactured by 
National Semiconductor. 
In accordance with the present invention there is provided, in addition to 
the X-axis and Y-axis output signals on lines 86, and 88, which are 
indicative of the corresponding X-axis and Y-axis positions of the 
actuator or control member 20, an especially simple yet highly reliable 
supplemental "neutral" position indicator which functions as a redundant 
or back-up confirmation of the position of the actuator member 20 when it 
is in its neutral position. The supplemental indicator is shown in FIGS. 
1, 6 and 7, and is seen to be entirely separate and distinct from the 
sensors 38, 40, 42, and 44 and the circuitry associated therewith, to thus 
enable a secondary reading of a "neutral" position to be accurately 
indicated. 
By the invention, the supplemental "neutral" position indicator comprises 
an emitter-sensor means 190, FIGS. 1 and 6, which preferably is in the 
form of a combined radiation- or light-source 192 and an 
electro-responsive device or light-sensor comprising a phototransistor 
194, contained in a single package as an optical-electronic chip. In 
addition, by the invention the bottom of the actuator member 20, indicated 
196, is provided with a light- or radiation-reflective transverse surface 
or area 198. In the present instance, this surface is preferably formed by 
nickel plating a mirror-like surface or layer on the end of the member 20. 
The surface is preferably planar, and lies perpendicular to the axis of 
the member 20. The nickel plated surface is polished to produce a 
reflective or shiny characteristic. Typically the reflective surface has a 
cross-dimension of substantially 0.030-0.040 inches. Other types of 
reflective means could be employed, such as a separate mirror affixed to 
the bottom of the member, as can be readily understood. The use of a 
nickel plate has been found to be very economical, however. 
The emitter-sensor means 190 is mounted physically within the base 14, at a 
location just below the bottom end 196 of the actuator member 20, FIG. 1, 
such that there is no interference with the member 20 as it moves across 
its zone or field of travel, indicated 21 in dotted outline in FIG. 7. The 
light-source 192 emits a beam of light continuously, being powered from 
the +12 volt line, FIG. 6, through resistor 200. The light-sensor 194 is 
similarly connected to the +12 volt line through a load resistor 202. 
Output voltage on line 204 changes according to the presence or absence of 
light striking the sensor 194. The sensor 194 comprising the 
phototransistor is rendered conductive when it is struck by light, 
corresponding to a low output voltage on line 204, and rendered 
non-conductive in the absence of light, striking the sensor 194 
corresponding to a high output voltage on line 204. When the member 20 is 
disposed in an angular position other than its "neutral" position, there 
occurs little or no reflection of the beam by the reflective surface 198 
and the output 204 of the light-sensor 194 is high (i.e. a digital "one"). 
On the other hand, when the member 20 is near or at its neutral position, 
the light beam from the light-source 192 is received by the reflective 
surface 198 of the member 20, which in turn re-transmits much of the beam 
back toward the light-sensor 194, causing the output thereof, line 204, to 
assume a low level (a digital "zero"). The schematic diagram showing the 
electrical connections to the emitter-sensor 190 is given in FIG. 6. 
Output line 204 can connect to a suitable indicator (not shown). The 
indicator can take the form of a light or light-emitting diode (not 
shown), or alternately can be merely a buffer stage (not shown) whose 
output extends to suitable processing circuitry (such as a safety 
interlock circuit, not shown), as dictated by the particular requirements 
of the user. 
With such an arrangement involving an independent detector circuit, FIG. 6, 
that is mostly isolated from the circuit of FIG. 3, a highly reliable, 
independent back-up or confirmation signal is always present on the 
separate output line 204, to indicate when the member 20 is in its central 
or "neutral" position. The signal so obtained thus constitutes a separate 
and distinct digital-format confirmation signal, which supplements certain 
ones of the existing analog-type voltages obtained on the output lines 86 
and 88 of FIG. 3. 
This can have important advantages, as in the case where positioning of the 
member 20 at its "neutral" position must be positively verified, and in 
the event of a malfunction of one or both of the X-axis and Y-axis 
indicator circuits of FIG. 3. Significantly improved reliability results. 
There is greatly reduced the possibility of a malfunction of the system of 
FIG. 3 leading to injury to personnel, or damage to the equipment being 
controlled (not shown). 
Further, in accordance with the present invention there is provided a novel 
method of responding to the attainment of a neutral position of a joystick 
controller, as for example, that of FIGS. 1 and 3, comprising essentially 
the following steps: 1) providing a mirrored or reflective surface 198 on 
a minute area or end 196 of an actuator member or joystick 20, placing the 
joystick 20 in its neutral position, locating an emittersensor 
optical-electronic device or chip 190 in a position spaced a minute 
distance from the mirrored surface 198, and at a point where it does not 
interfere with the movement of the joystick 20, and thereafter 
electrically energizing the emitter portion 192 of the emitter-sensor 
chip, and conducting the electrical response of the optical sensor portion 
194 of the chip to a point remote from the chip, via a line 204. 
In the construction illustrated, the chip 190 can be of a type known by the 
part number SFH 900 or SFH 905, manufactured by Siemens. The chip 190 is 
known as a miniature light reflection emitter/sensor, and is readily 
available commercially. In this unit, the source and sensor are disposed 
side by side, in juxtaposition with one another as in FIG. 5. The 
preferred spacing between the mirrored or reflective surface 198 of the 
actuator member 20 and the chip 190 is typically one millimeter, which 
gives near optimal response characteristics. The distance between the 
socket 22 and the reflective surface 198 is typically 0.625 inch. 
The range within which the indicator of FIGS. 1 and 6 will provide a 
"neutral" reading has, in actual tests, been found to be on the order of 
0.5 to 2.0 degrees on either side of its center or "neutral" position. As 
noted above, this reading on line 204 is completely independent of that 
obtained by the position sensors 38, 40, 42, and 44 described above, and 
thereby provides a safety check or confirmation of the position of the 
joystick actuator member when the latter is in its neutral position. 
From the above it can be seen that I have provided an especially simple 
redundant-type neutral position indicator for a joystick controller, the 
device being both inexpensive to manufacture and produce, and highly 
reliable in operation, as a consequence of its relatively few parts. The 
position indicator is applicable to any type of joystick controller, 
either as part of the original equipment, or as an add on circuit. 
The independent nature of the electrical connections associated with the 
indicator render it largely isolated from the remainder of the joystick 
controller, and not subject to interaction therewith. 
The output from the indicator is in digital form, easily adapted for 
control of an interlock, or other safety type device. 
The present structural combination as thus described, and the method 
associated therewith, are thus seen to represent a distinct advance and 
improvement in the field of electromechanical controllers. 
Variations and modifications are possible without departing from the spirit 
of the invention. 
Each and every one of the appended claims defines an aspect of the 
invention which is separate and distinct from all others, and accordingly 
it is intended that each claim be treated as such when examine din the 
light of the prior art devices in any determination of novelty or 
validity.