Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an angular position indicator to provide
reliable and precisc angle sensing. More particularly, thc sensor of this
invention makes usc of the Hall effect.
The l-lall effect is the phenomenon known that if a thin semiconducting
plate has a current [I] along its length, then a voltage [E] will be generated
across its width in proportion to thc normal component of magnetic flux [B]
through the plate. Consequently, if one or more llall plates are placed in a
region of magnetic field, output voltages will be produced which are functions
of the flux angle. If a mechanical device is made such that relative rotations
between Hall plates and magnetic field is the input angle, then the output
voltage or voltages contain angle information.
Numerous devices have been patented to sense angular orientation
using the llall effect. lor example, Canadian Patent No. 478,884 issued
November 27, 1951, to HANSEN, entitled "Hall Effect Control Initiator" provides
an angular position indicator used with galvanometer type electrical instrument.
The patented device employes a tiny plate of material which exhibits the Hall
effect, together with a source of current excitation therefor and a magnetic
field producing means such as a permanent magnet. The Hall plate and magnet
are relatively movable in response to a measuring device rela~ with which the
control device is associated, such that at some predetermined measurement
value or signal, the Hall plate is cut by the flux of the magnet sufficient~y
to produce a control voltage. Because of the orientation of the magnet rela-
tive to the Hall plate, hysteresis effects may affect the accuracy of the an-
gular measurement.
Canadian Patent No. 486,337, issued September 9, 1952, to, HANSEN,
entitled "Hall Effect Telemetering Transmitter" shows a telemetering trans-
mitter for a selsyn type system. It uses a plurality of circumferentially
positioned Hall effect plates on a structure surrounding a magnet rotated with
a mechanically driven indicator arm shaft. A transmitter generator utili~ing
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the Hall e~fect is employed is said tO enable the construction of low-cost
reliab1e transmitters which do not re~uirc the use of moving contacts. In
this patented device, the permanent magnet was surrounded by the Hall effect
cylinder. Because of the orientation of the magnet relative to the Hall plate,
hysteresis effects may affect the accuracy of the angular measurement.
Canadian Patent 715,732, issued August 10, 1965, to RATAJSKI et al,
entitled "ila11 Effect Translating Device" relates to a shaft position trans-
lation device. In the patented device position is detected by means of the
Hall effect on a semiconductor body. Flux is applied to the semiconductor
body from a rotor, which provides angular position to be translated into an
electrical signal. In each patented brushless Hall effect potentiometer , a
high degree of resolution is said to be obtained. Ilowever, in that patent it
was necessary that the magnetic flux always cross the Hall plates at right
angles.13ecause of the orientation of the magnet relative to the Hall plate,
hysteresis effects may affect the accuracy of the angular measurement.
Canadian Patent 740,104 issued August 2, 1966 to Derek A. Rush pro-
vided a Hall effect electric position detection device which produce an elec-
tric signal in dependence on the position of a member. In the patented device,
pieces of a high permeability magn,etic material were arranged so as to form
a magnetic circuit cLosed except for at least one gap. Means were provided
to produce a variation in the magnetic flux in accordance with a variation
of the position of the means. A Hall effect device was disposed in a gap in
the circoit so as to be affected by variations in che flux. In operation, a
component of the HalL voltage of the Mall effect device was said to be a
direct voltage which has a magnitude dependent on the position of the means.
Because of the orientation of the magnet relative to the Hall plate, hysteresis
effects may affect the accuracy of the angular measurement. ~
;~ ; Canadlan Patent 836,179 issued March 3, 1970 to WiLllam B. Walton
provldes a displacement sensing transducer utilLzing a Hall generiting device
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as a scnsor. The patcnted dcvicc included a magnctic strip havlng a surfacc~
curved relative to the linc of movement and mounted on one object. Two Hall
cffcct sensors were mounted on the other objcct at a position to pass adjacent
the magnctic strip upon movement of the objects along the linc of movement
and spaced apart from each othcr in a direction substantially parallel to the
line of movement with each sensor adapted to produce an output signal varying
as a function of the magnctic field respectively applied to each sensor by
the magnetic strip. Means were provided which were responsive to the output
signals for producing a control output having a magnitude varying as a func-
tion of thc output signals. Bccaus~ of the orientation of the magnet relative
to the Hall plate, hystcresis effects may affcct the accuracy of the angular
measurement.
Canadian Patent 904,423, issued July 4, 1972, to LANG entitled
"Electric Pulse Generator" provides a pulse generator useful for measuring
Icngth of yarn or thread. In the patented pulse generator, a magnetic system
which rotates with the shaft effects a stationarily mounted Hall probe. The
Hall probe was positioned adjacent the magnetic system on a fixed plate which
preferably had a printed circuit thereon connected to the Hall probe. The
end of ~he shaft was magnetized itself or a magnetic member was affixed to
the end ol the shaft in the shape of an arc so that the field lines of the
magDetic field emerged from the magnetic system approximately coaxially with
the shaft. The radially emerging fleld lines of the produced magnetic field
~ vere guided to the Hail generator via ferromagnetic baffle sheets. Becausc of
i~ the orientation of the magnet relative to the Hall plate, hysteresis effects
may affect the accuracy of the angular measurement.
; Canadian Patent 980,450, issued December 23, 1975, to FREEMAN en-
citled "Autopilot Employing Improved Hall Effect Direction Sensor" provided
a Hall effect device flxed to a first member and a permanent magnet rotatable
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rclativc angular dcvia~ion bctwecn thc first and second members. The patcnt~d
invcntion, I~owcv(!r was dircctcd to thc llall-cffcct dircction sensor in conjunc-
tion with spccified elcctronic circuitry. The llall-effcct dcvice was madc
responsive to the angular rotation of a separate permanc~nt magnet whose posi-
tion in turn was controlled by a magnetic field or other condition to be
measured. The rotatable magnet was disposed in the central core and the llall
plate was also aligned thereto in the central core. 13ccaus(of the orientation
of the magnet relative to the Hall plate, hysteresis cffects may affcct the
accuracy of the angular mcasuremcnt.
Canadian Patent No. 1,001,736, issued December 14, 1976, to BABA
et al, entitled "Angular Position Detector Using Magnetic Elements" providcs
a shaft position sensor for producing an electrical signal representing an
angular position of a rotary shaft. It uses an asymmetrical-shaped or stepped
shaft extension, forming a pole piece or magnetic circuit structure. The
rotatable pole piece co-operates with fixed permanent magnets and fixed Hall
devices. It was thus necessary to provide two magnets with varying flux and
two Hall plates. Bccauseof the orientation of the magnet relative to the Hall
plate, hysteresis effects may affect the accuracy of the angular measurement.
~ Canadian Patent No. 1,046,541, January 9, 1979, MAKABE entitled
"Needle Position Detecting Arrangement For Sewing Machine" shows permanent
magnets mounted inside a drive pulley for driving the sewing machine main
shaft. These magnets co-operate with Hall devices to provide an output pro-
portional to needle position. In the patented invention, the magnet and the
Hall generator are accommodated between the machine housing and the pulley
so that the magnet, during rotation together with the pulley in synchronism
with the motion of the needle of the sewing machine, may be detected by the
Hall generator in a fixed position, and the position of the needle may be
accordingly detected. Bccauscof the orientation of the magnet relative to the
Hall plate, hysteresis effects may affect the accuracy of the angular measure-
ment.
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~ ustralian Patent 231,889, or Lawrcnce, C.J. Fricher ct al publishcd
February 26, l959, entitled "Improvemellts in transduccrs~, shows an angular
position transducer comprising a pair of llall plates sandwiched between two
pairs of angularly spaced iron blocks togethcr with a permanent magner. The
patented invention provided a transducer comprising in combination an element
made of a matcrial having the property of "llall" effect or magneto-resistance
when subjected to a changing magnetic field, a magnet, and means responsive
an input signal Eor varying the influence of the field of the magnet upon the
element. I3eca-lseof the orientation of the magnet relative to the Hall plate,
hysteresis effects may affect the accuracy of thc angular measurement.
The llall-effect sensors of the prior art as described above suffered
many deficiencies. The magnetic system could be difficult and expensive to
manufacture, since its manufacture could have required many operational steps.
In sensors where the crown magnet and the cup-shaped carrier constituted a
relatively large mass, the pulse generator was practically useless with ap-
paratus for measuring systems where the rotating parts must have very small
moments of inertia. Moreover, in many instances inaccurate measurements
resulted because of inaccurate compensation for temperature or acceleration.
~ Moreover, to achieve spatially correspondent master/slave control
for robot arm, joint angles in the master and slave arms must be measured
precisely. The prior art, including the above described Hall-effect sensors,
po~entiometers, and optical sensors was deficient for undersea applications
because of si~e, poor environmental isolation, fragility, and course digital
output.
Accordingly, it is an object of one broad aspect of this invention
to provide a joint anele sensor to implement the spatially correspondent master/
slave design concept.
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An object of another aspect of the present invention is to provide
an improved device for translating position into an electrical signal,
especially where such position is translated with improved resolution.
~y one broad aspect of this invention, a joint angle sensor is
provided for achieving spatially correspondent mater/slave controls com-
prising: an inner ring of robust, non-magnetic material within which is fixed-
ly disposed, and preferably is embedded, at least one Hall-effect plate; an
outer ring of robust non-magnetic material relatively rotatable with
respect to the inner ring, the outer ring having fixed therein, but pre-
]0 ferably embedded therein, at least two magnet poles to provide a uniform
magnetic field in the inner ring; a casing around the outer ring, the
casing being formed of a ferromagnetic metal; electrical connections for
the Hall-effect plate for applying a current along the length thereof and
for conducting voltage therefrom which has been produced across the Hall-
effect plates; means for relatively rotating the inner and outer rings;
and means for reading the voltage which has been produced across the
Hall-effect plate, that voltage varying as the sine of the angle of rota-
tion between the inner and outer rings.
By one embodiment thereof, the inner and outer rings are made
of epoxy resin.
By another embodiment thereof the magnet poles comprise two
ceramic magnets.
By yet other embodiments thereof, the magnet poles and/or the
Hall-effect plate, is embedded in an epoxy resin.
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sy still another embodiment thereof, the Hall-effect plates are
arranged and connected so as to null extraneous electrical effects caused
by temperature or pressure.
sy another aspect of this invention, an angle sensor is provided
comprising (i) a cap having an annular well extending inwardly from one
face thereof and a central well extending inwardly coaxially with respect to the
annular well from the other face thereof; ~ii) a pin projecting outwardly from the
one face and disposed within the annular well, the pin having a base in the
form of a hollow cylinder, the hollow cylinder having fixed therein and
preferably having embedded therein, an outer casing of ferromagnetic material
adjacent wall of the cylinder, the fixing material being a robust non-magnetic
material, e.g. an epoxy resin, t:he magnet poles being adapted to provide a
uniform magnetic field within the central well; (iii) means Eor providing
relative rotation between the pin (ii) and the cap (i); (iv) at least one
Hall-effect plate fixedly disposed, and preferably embedded with the central
well, the Hall-effect plate being provided with electrical connections for
conducting voltage therefrom which has been produced across the Hall-effect plates; and (v)
means for reading the voltage which has been produced across the Hall-effect
plate, the voltage varying continuously as the sine of the angle of rotation
ZO between the pin (ii) and the cap (i). Preferably the relative rotation~is
provided by having the cap fixed and by providing means for rotating the pin.
The embedding material used for the outer casing an'd for the
magnetic poles preferably is an epoxy resin. The magnetic poles pre-
ferably comprise Lwo spaced apart magnets embedded within the hollow cylin-
der In an epoxy resin, most preferably being in the form of two spaced
apart ceramic magnets embedded, along with the outer casing, in an epoxy
resin within the hollow cylinder.
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The Hall-effect plates are preferably interconnected Hall-effect
plates, embedded within the central core, e.g. by means of an epoxy resin.
Preferably, -the electrical connectors are individually encased within a
respective heat-shrink tubing and collectively encased by a common heat-
shrink tubing.
In the accornpanying drawings,
Figure 1 is a schematic view showing the principles of operation
of the angle sensor of a broad embodi~ent of this invention;
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Figure 2 is a top plan view of a commercial embodiment oE this
invention;
Figure 3 is a section along line III-III of Figure 2;
Figure 4 is an enlarged perspective view of the sensor elements
used in the commercial embodiment of Figure 2; and
Figure 5 is a circuit diagram of the commercial embodiment shown
in Figure 2.
As seen in Figure 1, the angle sensor 10 comprises an outer
ring 12 and an inner ring 11, each made of a robust non-magnetic material.
In one example, this is an epoxy resin, but other materials, for example
aluminum may be used. Embedded within inner ring 11 are a pair of Hall-
effect plates 14. As well known in the art, these Hall-effect plates may be
made from any semi-conductor material which has the characteristics of pro-
ducing an electric potential along one axis in response to an electrical
current and a magnetic field along respective axes normal to that material.
One example of such semi conductor material is a crystal of indium arsenide.
Other examples include bismuth, germanium, or other semi-conductor matexials.
Embedded within the outer ring 12 are one or more permanent mag-
nets 13 so arranged that a uniform magnetic field is provided in inner ring
11. The permanent magnets may be formed of any material having a high
coercive force, e.g. those known by the trade marks FERRIMAG, CRUCICORE
or ALNICO V, Preferably the magnets are ceramic magnets or other materials,
so selected that the magnetic flux is not a function of temperature or
;~ accelsration within operating limits. In order to provide magnetic shield-
ing from outside sources, and to complete the magnetic circuit, the sensor
or transducer 10 is encased in a ring of ferromagnetic metal 15.
As seen in Figures 2 and 3 the commercial embodiment of the
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sensor 10 previously identified as 10 is housed in oval shaped cap 100.
The sensor 110 (see Figure 3) is embedded in a sensor pin 120 which is in
the form of a cylindrical projection 121 terminating in a hollow cylinder
122. Within hollow cylinder 122 are sensor ring 115, corresponding to
ferromagnetic ring 15 previously described, and magnets 113, corresponding
to magnets 13 previously described, each embedded in an epoxy resin 112,
corresponding to outer-ring 12 previously described. Sensor pin 120 is
disposed in an annular well 123 in cap 100 in such a way that it may be
rotated by means (not shown).
The cap 100 is provided with well 111 at the central core
therecf, corresponding to inner ring 11 previous]y clescribecl~ w~thill
which are fixedly disposed the Hall-effect plates 114, corresponding to
the Hall-effect plates 14 previously described. Preferably the Hall-
effect plates are fixedly disposed by being embedded in an epoxy resin
filling well 11l. Wiring 131, 132, 139 and l40, to be described here-
inafter, emerge from the bottom of cap lO0.
The cap 100 is provided with the usual mounting apertures 132.
The structure of the Hall-effect plates 114 is shown in more
detail in Figure 4. The Hall-effect plates 114 are each provided with
positive terminals 125 and negative terminals 126, the respective wires 127,
from the positive terminals of each Hall-effect plate 114 being soldered at
129 to form a common positive wire disposed within a heat-shrink tubing 131,
the respective wires 128 from the negatlve terminals 126 of each Hall-effect
plate 114 being similarly soldered at 130 to form a common negative wire
disposed within a heat-shrink tubing 132. The third terminal 133 from one
Hall-effect plate extends as wire 135 which is soldered at 137 to a third
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terminal within a heat-shrink tubing 139, the third terminal 134 Irom the
other 11a11-effect plate extending as wire 136, which is so1dered at 13
at heat-shrink tubing 140.
For proLection thereof, and to provide a rugged structure,
wires 127, 128, 129, 130, 135 and 136 and heat-shrink tubings 131, 132,
137 and 140 are all disposed within heat-shrink tubing 141 extending
from Ha1i-effect plate 114, the heat-shrink tubing 141 being shown in
broken lines for clarity.
As seen in Figure 5, wires 131 and 132 provide excitation to
Hall-effect plates 114, while wires 139, 140, transmit the signal from
the Hall-effect plates 114.
Thus, as noted above, the sensor of this invention is basèd on
the Hall-effect. It consists of two parts: a set of magnets embedded
in an outer ring of epoxy, and a set of Hall-effect semi-conductor plates
embedded in an inner ring of epoxy. As one or the other ring rotates,
a voltage proport1onal to the sine and/or cosine of the angle of rotation
is generated. This voltage is produced continuously with infinite resolu-
tion, and may be used directly to infer the angle of rotation, or, if
; pulse counting hardware is available, to infer more than one rotation.
- 20 m e inner ring consists of one or more Hall-effect plates embedded
in epoxy. If more than one Hall plate is used, (a preferred embodiment)
the plates may be arranged and connected ;so as to eliminate (or null) electric
~effects caused by temperature, pressure, etc.
The outer ring consists of one or more magnets embedded in epoxy,
placed so as to provide a uniform magnetic field in the inner ring. Since
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in the rotating f1eld, no effects due to hysterysis are obsèrved. If the
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preferred magnets, ceramic, are used, the magnetic flux is not d function
of temperature or acce]eration, wit:hin wide operating limits.
The above-described embodiment of the sensor or transducer of
this invention is unique in that it uses the ~iall-effect directly to
induce a continuously variable voltage directly from the defining char-
acteristics of the iiall-effect, which results in infinitely fine angular
resolution. Other liall-effect transducers produce voltage peaks from
ridges or teeth cut in a moving part, or measure irregularities in the
magnetic field, and therefore provide only crude angular information.
Further, the transducer of this invention is very insensitive to outside
influence.
The above-described sensor or transducer of this inventior~
has infinite resolution and is very robust. It has no moving parts other
than inner and outer ring relative rotation; it can never wear out; it
is virtually insensitive to temperature, opacity of environment, pres-
sure, vibration, acceleration, and electromagnetic fields; and it can
easily be made insensitive to corrosive environments.
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