Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
lZ~2661
~IELD OF THE INVENTIQN
The present invention relates to a force and torque
converter and has useful applications in a wide field of
activities particularly where a manual motion ~s to be
converted into a cont~ol ~signal~. For esample, machines such
as industrial robots, back hoes and computer graphic
works~ations have comples control reguirements.
BAC~QUND TO THE IEY~TIQ~
In esisting systems, control of a vehicle such as a back
hoe is achieved by manipulation of levers and more ~ecently by
joy sticks. In computer applications joy sticks are a common
control system but a computer may also employ a ~track ball"
or a ~mouse~. These devices have limited directions of motion
~ and accordingly limited commands only are possible.
In addition to a control system, there is also a need for
a sensing system to monitor applied forces and torques; an
esample of such a sensor system is a system for monitoring
applied forces and torques with respect to three a~es in a
manipulator (see United States Patent 3 921 445 Hill and
Sword). In that specification the manipulator is of a hand
like form comprising a pair of jaws which are relatively
pivotally movable under operation of an electric motor. The
manipulator is defined as having a wrist and sensing means are
provided for sensing the magnitude and direction of forces
along three mutually orthoganal a~es intersecting at the wrist
and for sensing the magnitude and direction of torques about
the axes. The form of the sensing means is a series of
sensors extending around the longitudinal asis of the
manipulator.
~SUMMARY OF THE INVE~TION
In one aspect, the present invention consists in an
apparatus for providing output signals for use as command
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fiignals with respect to X, Y and Z mutually osthogonal a~es,
the signals being representative of a translational applied
force and an applied torque, the apparatus comprising a ~ase,
a body to which the forces and tor~ues are applied, resilient
S connecting means attached to the body and mounting the body
for receiving force in any direction ana torque about any asis
and for resiliently resisting displacement of the body from a
normal position relative to the base, and sensor means
arranged to detect a response to and to provide said output
signals corresponding to components of an applied torque and
components of an applied translational force with respect to
said ases, and wherein said sensor means comprise either (a) a
sis sensor unit configuration arranged in a three dimensional
substantially uniform array with respect to said X, Y and Z
ases, the sensor units being arranged in pairs for detecting
displacement along a respective operating axis, a first pair
of said sensor units having an operating a~is in the X
direction, a second pair of said sensor units having an
operating asis in the Y direction and a third pair of said
sensor units having an operating asis in the ~ direction, each
of the sensor units being non-responsive to any displacement
at right angles to its operating axis, whereby the output
signals may be processed to provide a command signal
corresponding to any applied torque or any applied
translational force, cr (b) a four sensor unit configuration
arranged in two pairs and in accordance with two of the three
pairs of sensor units in said six sensor unit configurat;on.
In the preferred embodiments described below, a very
small displacement results from each of the translational
force and applied torque, the connecting means being biased ~o
a central position. However, it is possible to embody the
invention in a form in which no displacement takes place and
instead sensors respond whereby a signal is derived
representative of the force or torque tending to cause
displacement at each sensor. For example, a system in which
automatic control causes the input of some energy to resist
the displacement could be used, the input of energy having a
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corresponding signal generated for indicating the magnitude of
the applied force.
The invention is especially ~aluabl~ in permitting
embodiments in which the applied translational force and/or
the applied torque are respectively resolved into components
with respect to most prefera~ly three mutually ~erpendicular
ases. Hereinafter the invention will be e~emplifed with
reference to the most comples esample ~n which a three
dimensional device is utilised and it w;ll be appreciated that
a comples ergonomically designed contro~ system can utilise an
apparatus of this form. It is envisage~ that for many
applications a handle or grip for an operator will be provided
and this grip is adapted to receive a t~nslational force and
a torque, the translational force being applied in any
direction and the torque being about a~ desired a~is. The
output signals can be used to control a~y required device and
sophisticated control of, for esample, a machine can be
achieved with just one control member. ~his can be very
important for the control of complex ma~hines which require an
operator to use a multiplicity of separ~ite levers for
controlling, e.g. hydraulic circuits. ~nother area in which
there may be very beneficial applicatio~3 is for control of
devices for handicapped persons.
In a preferred embodiment the appa~tus is such that only
at most very small displacement results from the applied
translational force and~or torque. In ~;he mechanical examples
described hereinafter the mathematical ~rror resulting from
displacement is at most exceedingly sma~l and may be
disregarded for very small angles of di$placement.
In one specific embodiment, the fi~ed base has a portion
at which the X, Y and Z axes intersect and the connecting
means comprise respective pairs of resiliently deformable
connecting arms extending in the Z and ~ directions, the arms
of each pair extending away from the ba~se portion in opposite
directions to be connected to the body, and wherein the sensor
means are adapted to detect a displacement in the respective
connecting arms and provide signals permitting computation of
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the applied torque and/or force, the sensor means detecting
torque about the Y axis or displacement in the X direction at
respective locations in the arms e~tending in the Z direction
on opposite sides of the X axis, and detecting torgue about
the X a~is or displacement in the Z direction at respective
locations ~n the connecting arms e~tending in the Y direction
on opposite sides of the Z a~is.
Preferably, ~he apparatus described in the previous
para~raph is such that the remote ends of said arms are
constrained against movement in second and third mutually
perpendicular a~es, which are each perpendicular to said first
asis.
When the embodiment of the preceding paragraph is applied
to a three dimensional version, then the connecting means
comprises three pairs of arms eYtending mutually
perpendicularly and co-operating with the body so that the
respective pairs of arms are constrained about respective
mutually perpendicular axes.
Apparatus according to the invention preferably includes
signal processing means for processing the signals detected at
the respective sensor means whereby output signals correspond
with the applied torque and the applied translational force
and, in the case of a three dimensional version of the
invention, the output signals represent the resolution of the
applied force and applied torque with respect to three
mutually perpendicular axis.
A second important embodiment of the invention is one in
which the connecting means comprises a series of three
connecting structures each comprising an arm extending from
the body and pivotally connected through a joint having
universal action through at least a limited range of angles to
a leg, the leg extendinq normally in a direction substantially
at right angles to the arm to be attached to the fi~ed base,
the biasing means biasing the leg to a central position and
the leg having an ability to move aqainst the biasing in a
plane being substantially that containing the pivot point of
the universal joint and substantially perpendicular to the
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axis of the leg.
Preferably, a universal joint providing a limited range
of motion is used for the pivotal connection between the leg
and the arm.
Preferably, the apparatus is arranged such that each of
arms of the connecting structur~s has its pivotal connection
with its leg member 6uch that a reference a~is of the
connecting member extends rom a central point in the body
through the pivotal connection and this reference a~is is
substantially at right angles to the asis along which
displacement is sensed by displacement of the pivotal
connection.
Preferably, each leg member is arranged to e~tend at
right angles to the reference asis of the associated
connecting member, the remote end of the leg member being
fixed.
Preferably, the biasing means includes resilient
deformability provided in the leg member and for this purpose
preferably a reduced diameter portion is provided in the leg
member near its remote fixed end.
An important embodiment of the invention consists in an
apparatus for transforming applied forces into translational
components along three mutually perpendicular axes and torque
components about these three axes, the apparatus comprising a
body to which the force is applied, three connecting members
attached to the body and extending away therefrom such that in
a central position of the body remote connection points on the
respective connection members lie along respective reference
axes extending from a central point of the body, these
reference axes being mutually perpendicular, respective leg
means being pivotally connected to the respective connection
members at said connection points through universal joints of
limited range and motion, biasing means being provided to bias
the connecting members towards the central position and sensor
means for sensing displacement of each connecting member
and/or each connecting leg whereby the nature of the applied
force may be determined.
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For this important embodiment an effective mechanical
design is one in which the body is a ball-like member and each
of the connecting members is generally L-shaped and extends in
a plane at right angles to the corresponding leg member, the
S arm of the L connected to the ball-like member estending
through the ball mem~er and being pi~otable ~bout its own asis
which e~tends at right angles to the leg member and at right
angles to the reference asis of the connecting ~ember, anB the
other leg of the L having a universal joint located upon the
reference a~is.
To facilitate a stable and durable mounting, the arm of
the leg of each connecting member passing through the
ball-like body can be of a cranked design to permit
overlapping of the three respective arms.
Preferably, the sensor means associated with each
connecting member is arranged to operate substantially in a
plane and is arranged to monitor motion transverse to the
reference axis of the connecting member and motion along the
reference axis.
- 20 Where the device has three reference axes, rotation of
the body about a first axis will cause displacement at the
sensors mounted by a connecting members having reference axes
perpendicular to the axis about which rotation takes place.
This is due to an applied couple; there are equal and opposite
reactions.
Since the invention will normally be applied in a
situation in which only small motions are monitored,
references to planes and motion in planes (although
representing an ideal situation) will not necessarily
precisely describe the motion which in fact occurs. The
motion which occurs in one embodiment is planar, but in other
embodiments is over a small portion of a near-spherical
surface, but for the small motions envisaged, these motions
can be treated in practice as essentially planar motions and
will be described in this specification as being planar.
Preferably, each sensor has a planar plate and motion is
detected by a light emitting means and light detecting means.
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Advantageously a data processing means collates the
detected movements of the three sensor plates and produces a
signal representative of the effort applied to the body of the
apparatus, which may comprise translational motion, rotational
motion or combinations thereof.
RIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described by way
of esample only with reference to the accompanying drawings in
which:
Figure 1 is a schematic view of a first embodiment of the
invention;
Figure 2 is a plan view of the first embodiment in
practical form with the top of the spherical hand grip removed;
Figure 3 is a partially broken away side-view of the
first embodiment with the top of the hand grip removed and the
front portion of the arm structure in the middle region just
above the central plane omitted;
Figure 4 is a perspective view illustrating the
principles of a second embodiment in which the mounting
structure is directed externally from the hand grip
arrangement;
Figure 5 is a sectional elevational view of a practical
embodiment corresponding to Figure 4 and looking along the Y
direction at the device as seen in the X-Z plane;
Figure 6 is a plan view of the embodiment of Figure 5;
Figure 7 is an enlarged view of a preferred form of
mounting for the respective legs of the embodiment of Figures
5 and 6;
Figure 8 is an elevation of the embodiment of Figure 7;
Figure 9 is an inverted plan view of the embodiment of
Figure 7;
Figure 10 is a plan view of an alternative embodiment of
connecting arm for use with the operator hand grip shown in
Figures 12 and 13 and corresponding to the arms 33A, 33~ and
33C of Figures 4 to 6;
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Figure 11 is an elevation of the mounting arm of Figure
10;
Figure 12 is an a~ial cross-sectional ~levation of a ball
like operators hand grip for use with mounting arms as in
Figures 10 and 11 in an apparatus functioning in a manner
equivalent to Figures 4 to 6; and
Figure 13 is an inverted plan view of the operator's grip
shown in Figure 12.
- The theory behind the operation of the first embodiment
can ~e more easily understood by referring to the schematic
diagram of Figure 1 which illustrates an embodiment with the
mounting arrangement internally disposed relative to an
operator~s hand grip. Three pairs of leaf-spring elements
lOA, lOB and lOC are attached to a metal base 8 and e~tend in
three mutually perpendicular planes; the center lines of the
leaf-spring elements intersect at the centre of the base 8,
and extend respectively along X, Y and Z ases.
The leaf-spring elements lOA, lOB and lOC are
substantially of the same length and each leaf-spring element
has at the end distant from the base 8, a ball-like tip llA,
llB and llC which lies within a respective slot 12A, 12B and
12C in a hand grip 9 represented by a frame. Each slot
provides constraint of the corresponding tip against movement
relative to the grip in a direction perpendicular to the plane
of the corresponding leaf spring. Thus, for esample a
displacement force applied to the grip 9 along the Z asis
causes bending of the leaf-springs lOB only and strain gauges
(not shown) measure the bending so that a signal corresponding
to the displacement force can be produced. Each tip has a
freedom of motion relative to the grip 9 in the plane of the
corresponding leaf-spring. Thus, displacement of the hand
grip along the direction of elongation of a leaf-spring, or
across the direction of the leaf-spring does not result in any
bending of the leaf-spring.
A displacement force at an angle to each of the a~es is
resolved into corresponding bending components in all
leaf-spring elements.
-`-` l.Z92~i6~
Similarly, a torque applied to the hand grip is resolved
into corresponding couples about the respective X, Y and Z
ases. For e~ample, torque about the Z a~is causes equal and
opposite bending of the leaf-springs lOA as the respective
tips are deflected.
Forces applied along each of the ases and torques applied
about each of the a~es can be eguated as follows:
FX ~ Rl ~ ~2 TX ~ R5 - R6
Fy . R3 + R4 Ty - Rl - R2
Fz , R5 ~ R6 ~z , R3 - R4
where FI represents a force in the I direction, ~I
represents a torgue about the I axis and Rl to R6 represent
relative displacements in the directions indicated.
When a force is applied to the hand grip 9 in the X
direction, there is a corresponding slight bending of one pair
of leaf-spring elements lOC such that one element of the pair
bends a distance equal to Rl and the other element bends a
distance equal to R2. The resultant force in the X direction
is thus given by Fx = Rl + R2.
Similarly, if a torque is applied about the Y axis, one
of the leaf-springs of a leaf-spring pair lOC bends and
produces a displacement of Rl, while the other leaf-spring of
the same pair bends and produces a displacement of R2 in the
opposite direction. The resultant displacement about the Y
axis is thus given by ~y = Rl - R2. The remaining forces
and torques are calculated in a similar manner.
In practice an apparatus as shown in Figures 2 and 3 is
used to implement the principles shown by the schematic
diagram of Figure 1 in which like parts have been given like
reference numerals. ~he sensing apparatus is supported by a
fixed supporting rod 3 above a ground plane, the rod
connecting to a central mounting block 8. A force or torque
applied by an operator's hand placed on a spherical hand grip
9 is converted into its individual mutually perpendicular
components by means of an optical detector. In this
embodiment each of the X, Y and Z leaf-spring elements
consists of a pair of flat resilient metal strips spaced apart
-- 10 --
lZ~Z6~
and secured by screws 7 to opposite faces of the central cubic
mounting bloc~ 8 and at their remote ends the ~trips are
interconnected b~ a connector 13 having screws which also
attaches an end fitting 14. The end fitting 14 has an asially
e~tending shaft terminating in the ball like tip lLA, llB or
llC.
In this em~odiment, the optical detector associated with
each leaf-spring comprises a light emitting diode ~LED) 2 and
a photodiode 3 fi~edly mounted on a bracket 4. Each bracket
is mounted on a respective mounting bar 6 secured by screws 7
to the central bloc~ 8, with a packing block 6A and the
central part of the leaf-spring element being sandwiched
between the mounting bar 6 and the central block 8. A shutter
5 is attached to the end fitting 14(which interconnects the
leaf-spring metal strips) and thus movement of the shutter
alters the e~tent to which
the radiation of the LED 2 can fall on the photodiode 3. Thus
displacement is determined by alteration of current in
electrical circuitry. Each photodiode is connected through
wiring for electronic circuitry where the necessary
computation of force and torque takes place.
Referring to Figure 4, a second embodiment is shown
wherein a hand grip 30 is represented by a mounting ball 31 to
which shafts 31A, 31B and 31C are affiYed. The hand grip 30
is mounted through a set of three L-shaped mounting structures
pivotally mounted on the respective mutually perpendicular
shafts. The mounting structures comprise V-shaped arm members
33A, 33B and 33C and respective leg members 32A, 32B and 32C
which connect the hand grip 30 to a base 34.
Each of the arm members 33A, 33B and 33C is V-shaped and
hingably connected to the corresponding shafts 31A, 31B and
31C for pivotal motion respectively about the X, Z and Y
aYes. Each of the arm members is connected to a respective
leg member 32A, 32B and 32C through a ball joint 35 which
provides a limited range of universal relative motion. The
base of each leg member is fixed to the base 34 and includes a
narrow portion 36 near the base to provide a region of
1292661
preferential bending. Each leg is of a spring metal material
and has inherent resilience biasing the leg to the position
shown in the drawing.
In use a force and or torque applied to the grip 30
results, in the general case, in a displacement of each of the
respective arm-leg member connections and in particular
displacement at the respective ball joints is detected. In a
practical embodiment a detection plate assembly would be
mounted near each ball joint to enable accurate measurements
of deflection in a substantially planar surface perpendicular
to the asis of the respective leg 32A, 328 or 32C. It can be
shown that ths force and torque components applied to the grip
can be calculated from the respective displacements by the
following equations:
FX = Rl ~ R2 TX = -R3
Fy = R3 ~ R4 Ty = -R5
Fz = R5 ~ R6 Tz = -Rl
where FI is a force applied in the I direction, TI is a
torque applied about the I axis and Rl to R6 represent the
relative displacements of each respective ball joint as sh~wn
in the drawing.
The schematic diagram shown in Figure 4 is useful for
understanding the principles behind the operation of the
second embodiment: however, a construction as shown in
Figures 5 and 6 is a practical embodiment.
The complexities associated with the construction of the
second embodiment can be more readily understood by
considering one of its mutually perpendicular planes. Thus
referring to Figure 5, an X-Z plane is shown with the Y asis
perpendicular to the plane of the paper. The apparatus hcs
corresponding construction and function when considered ir~
either of the other two perpendicular planes. In the
embodiment of Figures 5 and 6 the same reference numerals have
been used for the parts corresponding to the structure shown
in Figure 4.
Figure 5 is an axial section through the ball-like g-ip
30 which is adapted to fit comfortably in the operator's
- 12 -
lZ92661
hand. The hinges represented by the mounting shafts 31A, 31B,
31C of Figure 4 are replaced by respective cranked
cross-shafts 31~, 31B and 31C which o~tend from just one side
of the ball grip 30 and comprise part of the respective arms
33A, 33B and 33C. The cranked profile of each ~haft is to
permit the three mutually perpendicular ~hafts to pa~s
diametrically through the ball and to cross over one another
thereby permitting the shafts to be rotatably mounted ~t each
end at bearing points 40 within the ball grip. ~he free end
of each shaft is secured by a screw 45 and washer 44, a part
spherical cap 46 being secured over the free end of the shaft
by screws 43.
Each ball joint 35 comprises a part-spherical ball member
35A mounted on the leg 32A, 32B and 32C with a corresponding
tip element 35B (with a part-spherical cavity) mounted on the
end of the respective arms 33A, 33B and 33C. A screw threaded
e~tension 35C extends beyond the ball joint from the leg and
the ball joint is assembled by a first securing nut 38. A
sensor assembly 39 is then fixed on the screw threaded
e~tension and secured in place by a second nut 41.
The sensor plate assembly 39 mounted on the end of arm
33B extends generally in the X-Z plane. The sensor plate 39
is of opaque material and is adapted to interrupt to a
variable and partial extent the passage of light from light
sources 42 which are directed towards light dependant
resistors 47.
Reference will now be made to Figure 7 to 9 which show a
preferred and alternative mounting arrangement for the
respective legs of the embodiment of Figures 4 to 6. One
mounting unit is shown in each of Figures 7 to 9 and has the
general feature of providing true displacement in a plane,
whereas in the arrangement of Figures 4 to 6 the displacement
is in a very small arc of a sphere and is thus not true planar
motion and very small errors are introduced into the results
obtained.
In Figures 7 to 9 the parts for mounting the ball grip
corresponding to leg-arm combination 32A, 33A are shown; like
- 13 -
12~2661
reference numerals are used or like parts.
A rigid base plate 34 is adapted to be fixed to a rigid
mount so as not to move in space. The mounting arm 33A is
pivotally connected to the hand grip (not shown) and is
connected to the base plate 34 through a resiliently
displacable mounting leg arrangement; the ~rm has a ball joint
including a ball 35A estending from the arm 33A and engaged in
a seat of the mounting leg arrangment. This leg arrangement
comprises a generally pear-shaped rigid plate 32A providing a
seat for the ball 35A, a first set of spring legs 36A, a rigid
connecting disX 36~ and secondary spring legs 36C estending
parallel to the first set of legs and connected to the base
34. The respective sets of legs are alternately spaced
equally around a circular path and thus form essentially a
~ ples spring structure. Any motion of the mounting arm 33A
~n a plane parallel to the plate 32A causes the three spring
legs 36A to be bent resiliently into a shallow S-shape,
reaction occurs through the disk 36B, and the secondary legs
36C bend resiliently into a corresponding S-shape bent in the
opposite direction. Thus, an applied force to the hand qrip
30 causing displacement of the arm 33A in the relevant plane
causes motion of the plate 32A and thus motion of an attached
shutter 39 in;a parallel plane thereto. Displacement is
detected by the degree of interruption of a light source (not
shown) inpinging on photodiodes 47.
From Figure 8 it will be seen that the shutter 39 has
operating edges 39a and 39b extending at right angles so that
displacement in the plane is resolved in two components. The
shutter is mounted on a mounting shaft 39c extending from the
pear-shaped plate 32A through an aperture in the rigid base
34, the rigid base carrying the photodiodes.
Figure 7 shows most clearly respective bosses 36D through
which the resilient legs 36A ex~end, these bosses estending
into respective apertures in the base 34. Any excessive
movement of the arm 33A causes one or more of the bosses to
abut the wall of the corresponding aperture thereby providing
a limit to movement.
- 14 -
125~Z661
An alternative and advantageous embodiment is a variation
on that of Figures 4 to 6 and wherein the mounting arm is
formed as shown in Figures 10 and 11 and the hand grip is as
formed in Figures 12 and 13. The operating principles are the
same, but the construction has advantages.
As shown in Figures 10 and 11, the mount~ng arm
referenced 33A has a generally Y-shaped physical form having
respective ends 50, 51 and 52. End 50 has, e~tending
laterally therefrom, the ball 35A for connection to the
mounting leg (or plate 32A as shown in Figure 9), End 51
terminates in a sleeve like tip 51a with an aperture e~tending
therethrough (along the X asis) and aligned with a small bore
estending obliquely through the tip region of the arm 52.
The hand grip shown in Figures 12 and 13 is of plastics
material and has a spherical ball-shaped head and a circular
base plate 30a, and is adapted to be connected to a set of
three arms of the type shown in Figures 10 and 11. The base
plate 30a has a series of three spaced inclined bores 30b
e~tending from chamfered surfaces and respectively along X, Y
and Z a~es of the apparatus. A series of three a~ially
aligned corresponding bores 30c are provided in the top
portion of the spherical head. Figure 12 shows a section
along the X asis. The arm end 51 of the mounting arm of
Figure 10 and 11 is secured by a bolt to the tapped bore 30b
and the end 52 of the arm is inserted through a corresponding
interior bore 30d in the spherical head so that the tip of the
arm has its oblique bore aligning with the bore 30c for
accommodating a securing pin. The pin is threadably engaged
in the bore 30c, but is a s~iding fit in the oblique bore in
the arm end 52.
Thus, the mounting arm has a limited freedom to rotate
about the X asis at its connection with the ball-shaped head
and freedom about the Z-axis at its connection with the
mounting leg arrangement, as conceptually shown in Figure 4.
Therefore, any displacement force on the ball-shaped head and
along the X asis or a torque about the X axis results in no
displacement of mounting leg 32A associated with arm 33A but
lZ926 61
in either case the other mounting legs may be displaced and
thus the motion detected.
The ball-shaped head includes a central interior bore 30e
for clearance purposes for the respective arm ends 52.
The invention can be applied to the control of an
industrial robot, whereby pushing and twisting motions of the
operator' 8 hand on the grip 30 causes corresponding motions at
the respective sensor plate assembly and by computation in
accordance wath the above eguations the applied forces ana
torgues can be determined. This permits corresponding motion
to be controlled in the robot.
A further advantageous application of the present
invention, in general, e~ploits the ability of embodiments of
the invention to detect and measure orce and/or torque
applied relative to two parts. An illustrative e~ample is the
case of a connection between two aircraft flying in formation
and connected by a refueling device. The invention could be
incorporated in a coupling whereby the relative applied
translational forces and torques between the two aircraft are
detected and monitored and indeed in a sophisticated
application this might cause the control systems of the
aircraft to automatically compensate as may be necessary to
keep the applied forces and torques within allowable ranges.
