Note: Descriptions are shown in the official language in which they were submitted.
MULTI DIMENSIONAL FORCE-TORQUE HANn CONTROLLER
HAV_NG FORCE FEEDBACK
This invention relates to a hand controller or 'cursor' for the
control and actuation of a wide variety of apparatus ranging from large
mechanisms requiring relatively large forces to effect movement, at one
extreme, to high precision devices requiring extremely fine motional control
on the other end of the control spectrum. More specifically, the present
invention relates to a multi-dimensional cursor suitable for control of
apparatus along the three linear orthogonal axes as well as about three
orthogonal torsional axes. The present invention further relates to an
interactive force-feedback cursor permitting the user to "fesl" the actual
forces encountered by a slaved apparatus in response to manipulation of the
control cursor.
The present controller is particularly suited for remote control
of objects in hostile or otherwise inaccessible environments. Examples
include airless environments such as the ocean floor or outerspace and
radioactive environments such as the interior of a nuclear power station
containment chamber.
In addition, certain environments are relatively inaccessible
simply due to the travel times required to reach these remote locations. A
highly skilled surgeon possessing, for instance, a certain specialized and
unique capability could perform an emergency lifesaving procedure utilizing
the present controller where there is insufficient time to travel to the
actual remote site of the operation. In essence, the surgeon may be,
effectively, in several locations at once. Other locations are simply
inaccessible irrespective of the time available to get there.
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Yet another significant application for the present controller is
force and/or motion amplification/attenuation in which either the size or
weight of the object or "work piece'1 on which the controller is to operate
requires that the range of movement or forces applied to the cursor (master)
be scaled appropriately for application to the slaved mechanism.
The surgical procedure previously considered illustrates an application
of the present controller wherein both the force and distance may advantageously
be scaled. The extremely light forces and fine movements required for a
microsurgical operation on a human nerve tissue, for example, may be scaled so
that relatively greater forces and movements must be applied to the cursor by
the surgeon. This permits the surgeon to make relatively gross hand motions with
correspondingly increased cursor actuation forces without injury to the patient.
In this manner, the surgeon can obtain a meaningful feel or touch for the work
being performed where otherwise the extremely fine and precise nature of the
procedure would fall below the threshold of human sensation thereby rendering
"touch" sensory feedback impossible. Furthermore, this increased sensory "feeln
obtainable with force/distance scaling lessens the likelihood of mistake or injury
occasioned by the inadvertent application ox excessive forces. Such down-scaling
also finds application in the manufacturing or assembly of precision apparatus
comprised of small or microscopic sized components.
At the other end of the spectrum, the scaling permitted by the
present invention cnn be utilized where the workpieces are relatively heavy or
where these objects must be moved over substantial distances. Applications for
such force/distance up-scnling may be found in most heavy industrial
environments, for instance in a foundry or automobile assembly plant.
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Yet another application for the present controller is the purely
'imaginary' or 'synthetic' environments generally created by computer. In a
computer aided design facility9 for example, it is often less expensive, and
faster, to 'sculpt' or create the proposed new article utilizing computer
graphics prior to committing to actual fabrication of a tangible model In
this way, it is possible to view and review alternative approaches at low
cost before commencing actual model fabrication. Thus, the present
forc~feedback controller permits a designer to literally sculpt his model,
with all the attendent visual and motor feedback sensations, as if the
object were a¢tually being modeled in clay or other material.
The present invention, however, is not limited to interactions
with things which can actually be built. Purely imaginary constructions or
'untouchable', but real, objects may also be probed utilizing the present
force-feedback cursor. One such example is the probing or manipulation of
atoms, molecules, or other atomic particles. While such particles exist, in
fact, it is not possible to physically 'touch' these particles and,
therefore, probing must be accomplished with the present controller through
computer simulation.
Known pl ior art controllers suffer from one or more defieiencies
which render them unsatisfactory for precise multi-axes force-feedback hand
control. Traditional tjoystick' type controllers, for example patent No.
3,447,766 to Palfreyman, provide only a restricted degree of control
generally in two linear or torsional axes. Such limited motional control is
wholly unsatisfactory for precision interactive control wherein six degrees
of freedom of motion are required to permit fu11 movement of the slaved
apparatus. One known controller, U.S. patent No. 4,216,467 to Colston,
does provide a six axis output but does not permit actual movement
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of the cursor; rather, the output signals are generated in response to the
pressures applied to the otherwise inert controller actuator handle or cursor. In
this regard, the Colston structure is unsatisfactory for use in the interactive
force-feedback environment for which the present invention was specifically
designed. In addition, the Colston controller employs combined
tension/compression members which, RS discussed below, have certain control
system disadvantages.
Another deficiency of known controller structures relates to the
force-feedback requirement and, specifically, to the complexity of the
control systems necessary to eliminate closed-loop instabilities commonly
flssociated with interactive controllers utilizing tension/compression force
translating members. Mechanical linkages which are alternately operated in
the compressive and tension modes or servo or torque motors which deliver
both positiYe and negative output forces often exhibit undesirable
'back-lash' or other discontinuities, non-linearities, or regions of
non-monotonicity that can result in unpredictable and wlstable system
operation unless properly compensated by the controller circuitry. This is
due to the necessity that there be a continuous and smooth transition
between the regions of compressive and tensioned operation of the
interconnecting linkages and, similarly, that there exist a continous and
smooth transition between the positive and negative force outputs of any
servo or torque motor in the system.
N~echanical and electro-mechanical apparatus having the requisite
continuity of operation are quite expensive and, in some instances, simply
unavailable. Although sophisticated control circuitry may be employed to
overcome these inherent mechanical limitations; little expense is avoidéd
using this approach due to the cost of the control circuitry necessary to
correct these inherent deficiencies. While the specific characteristics
of ear h of the following prior art structures is not known in detailt it is
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believed that each such structure would exhibit undesirable mechanical back-lash
requiring expensive control circuitry for use as a precision work~iece controller:
Haaker, patent No. 4,221,516; Von Hacht, patent No. 4,021,715; Jelatis, patent
No 3,139,990; and Serrel, patent No. 3,133,649 response to the pressures applied
to the otherwise inert controller actuator handle or cursor.
The controller of the present invention, by contrast, utilizes an
arrangement of twelve tension-only lines interconnec$ing the cursor and the
torque motors, or another controlled device9 to effect full interactive
force-feedback control in all three linear and three torsional axes. In
this manner, the above described transition region effects are eliminated by
maintaining a positive tensile force on each line with its corresponding
unidirectional force from each respective torque motor. More specifically,
the present controller employs a four vertex tetrahedral cursor arrangement
suspended within a polyhedral (octahedral) supporting structure to properly
position and interconnect the cursor with the twelve tension lines and
thereby affording a high degree of user access to, and movement of, the
cursor.
It is therefore an object of an aspect of the present inverTtion to provide an
interactive force-feedback cursor and controller structure. The cursor
shall have six independent degrees of movement including three liner axes
and three torsional axes. Further, the eursor shall be suspended by
an arrangement of twelve lines that shall continuously be under tension.
An object of an aspect of the present controller is the application of specific
tensions on each control line in response to the movement of the cursor
and the corresponding travel of the slaved apparatus thereby providing
force-feedback to the user representative of the actual or simulated envi-
rorment encountered by such controlled device. object of an aspect of the invention is to
provide a torque rotor on each line whereby the tension on each line may be precisely
controlled by a computer or other motor control apparatus. An objec-t of
an aspect of the present invention to provide moans for rreasuring the length of each
of the twelve lines whereby the precise location and orientation of the cursor
may be determined, for example, by a controller computer. It is further
contemplated that piezo-electric transducers, or the like9 may be provided at the
slaved apparatus whereby signals representative of the forces actually encountered
by such slaved apparatus are provided for the force-feedback control of the
cursor or cursor torque motors.
Various aspects of the invcntion ore as fol lows
A controller for remotely manipulating object including:
a) a Gursor having a line attachment member for retaining
control lines in spaced relationship and a handle means connected thereto
for repositioning the attachment member;
b) a cursor support means surrounding the cursor having a
plurality of means adapted to receive control lines for axial movement
therethrough;
c) a plurality of control lines each connected at a first
end to the line attachment member and at a second end adapted for connection
to a controlled apparatus, each line directed through the line receiving
means of the support means wherein movement of cursor handle means
correspondingly actuates the controlled apparatus.
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A controller for remotely manipulating objects including:
a) a cursor having a line attachment member for retaining
control lines in spaced relationship and a handle means connected thereto
for repositioning the attachment member;
b) a cursor support means surrounding the cursor having a
plurality of mean adapted to receive control lines for axial movement
therethrough;
c) a plurPlity ox control lines each connected at a first
end to the line support member and at a ~e~ond end to motor tensioning
means, each line directed through the line receiving means of the support
means wherein the motor tensioning means is adapted to reel-in or play~ut
control lines as the cursor is manipulated within the support means.
A controller for remotely manipulating objects including:
a) a cursor including a line attachment member and a handle
means connected thereto, the line attachment member having your vertices
defining a tetrahedral geometry; means on each vertex for attaching three
support lines thereto;
b) cursor support means surrounding the cursor including
four corners defining a volume therebetween wherein the cursor is suspended
for manipulation;
c) means associated with each support means corner adapted
to receive three control lines for movement therethrough;
d) twelve control lines each having a first end connected
to a vertex of the line attachment member and a second end adapted for
connection to a controlled apparatus7 three of said control lines being
directed through the line reeeiYing means of each support means corner
whereby movement of the cursor handle means causes a corresponding response
in said controlled means.
Figure 1 illustrate the controller of the present invention
including a control computer, monitor, interconnected with a slaved
microsurgical engine;
Figure 2 is a side elevation view of the cursor of the present
invention;
Figure 3 it a front elevation view of the same cursor taken along
line 3-3 of Figure 2;
Figure 4 ii a side elevation YieW of the cursor control unit
including the cursor and cur30P support structure;
Figure 5 is R perspective view of the control unit of Figure 4;
Figure 6 it a geometric diagram in perspective illustrating the
relationship between a cursor line attachment vertex &nd the corresponding
support structure vertices; and
Figure 7 is a geometric diagram taken from the top of Figure 6
looking downwardly along the y-axis further illustrating the interrelation-
ships between cursor and cursor support structure vertices.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 represents a typical installation of the force-feedback
controller of the present invention as configured to perform microsurgical
procedures. The illustrated work station includes a control actuator unit 10,
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having a cursor 12 positioned generally in the center thereof, a console
or table 14 on which the controller is affixed9 a cGmputer terminal 16 with
CRT display, a video monitor 18 and camera 19, and a microsurgical operating
engine 20 havlng a knife or other slaved tool 21. Camera 19 is preferably
affixed to the surgical engine adjacent knife 21 to afford a clear video
picture of the patient or other 'work~iece'. Cursor 12 is operatively
interconnected through twelve tension lines 22 to cursor torque motors 24
positioned immediately below controller 10 and tnble 14.
operation, the surgeon sits at the workstntion console 14 with
an unobstructed view of monitor 18 and manipulates cursor 12. The changing
lengths of lines 22 are recorded by computer } 6 and translated into
corresponding movements of the microsurgical engine 2~. Depending upon the
particular procedure being performed, the force and distance outputs of the
cursor may be scaled down by the computer prior to outputting to the
surgical engine. The video camera 19 permits the surgeon to visually
observe the results of his operative activities on monitor 18 while,
importantly, the forces actually encountered by the microsurgical slaved
"tools" are translated by computer 16 to torque motors 24 thereby providing
a real-time interactive force-feedback response enabling the surgeon to
'feel' the operation in a manner similar to conventional operating
procedures.
Cursor 12, illustrated in figures 2 and 3, includes a handle
member 30 extending outwardly along one leg of a live attachment member
32. Attachment member 32 is comprised of four equally spaced legs 34
rigidly affixed to a center hub 36 thereby forming a regular tetrahedral
geometry defined by line attachment vertices 38. As will be described in
more detail below, three separate control lines are attached to each of
the four vertices 38, comprising twelve control lines in total.
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The cursor of the present controller may be suspended, generally, in a
octahedral structure preferably with the twelve control lines spaced equally
about a subtending sphere. (An octahedral, or eight~ided, figure is generally
defined by its twelve verticies.) However, for reasons pertaining to ease of
construction and cursor access, an irregular polyhedral arrangement is
recommended wherein the lines are brought to a plurality of independent vertices.
Figures 4 and 5 illustrate a preferred cursor support structure 11 defined by a
tetrahedral form wherein three control lines eminate generally from each OI four
vertices. the cursor support structure 11, shown, is comprised of three contoured
arms designed to enhance esthetic appeal while simultaneously minimizing user
contact and interference therewith during use. The four vertices are defined as
follows: an upper verte2c 42, a rear vertex ~4, a left front vertex 46, and a right
front vertex 47.
Interconnection and routing of the twelve control lines 28 is
best shown in Figures 4 and 5. Each of the lines 28 is routed from the
appropriate cursor vertex 38, through an opening provided in the cursor
support structure at respective vertices g2, 44? 46 and 47, through the
respective arm members 40, then downwardly through pedestal 48 to the
torque motors 24 therebelow. specifically, the three lines from upper
support structure vertex 42 attach to cursor vertices 38a,b,d; the lines
from rear support vertex 44 interconnect with cursor vertices 38a,b,c;
the three lines eminating from the left front vertex 46 attach to cursor
vertices 38a,c,d; and the lines from the right front support vertex 47
connect to cursor vertices 38b,c,d. In this manner cursor 12 is supported
generally in the center of the support structure 11 by the twelve control
lines 28 which, significantly, are each maintained under tension by res-
pective torque motors 24. As the cursor is variously repositioned within
its working region, approximately defined by the area between the support
structure vertices, the torque motors continuously adjust the lengths of
lines 289 as described in more detail below, to assure a predetermined line tension
irrespective of the position of the cursor or the fact that the cursor is being
moved closer to a given support structure vertex. Thus, a positive tension force
is present on each control line during normal operation OI the present controller.
The precise position and orientation of the cursor is uniquely
determined by the lengths of the twelve lines 28 between the respective
cursor and support structure vertices. Any convenient means for measuring
these line lengths may be psovided, for example, a shaft encoder on the
torque motor line spindles. The line length data is fed to computer 16
which performs the necessary calculations More particularly, the precise
location of any given cursor vertex 38a,b,c,d is determined by a
mathematical triangulation technique based on the lengths of the three
control lines interconnecting the cursor vertex with the support structure.
It will be appreciated that the overall position and orientation of the
cursor i9 fixed once the location of the four cursor vertices 38 is known.
The position of each of each cursor vertex may be determined utilizing the
same mathematical relationships, but appropriately referenced to the proper
three support structure vertices.
Figures 6 and 7 illustrate the mathematical triangul&tion technique
utilized to locate a cursor vertex. Specifically, Figures 6 and 7 show
cursor vertex 38c in relation to support structure verffces 44, 46, and 47
through which three control lines 28 interconnect cursor vertex 38c with
corresponding torque motors. The distances between the various supporting
structures vertices 44, 46 and 47 are, of course, fixed by that structure
and known. For the purposes of this illustration, it is assumed that the
distances between each pair of certices 44, 46, and 47 is one unit.
a ~3 7~ 5i
The angle Al is determined by applying the well known 'law of
cosines' relationship as follows:
COS(Al) = (L~)2 1 - (L3)2
2 oL2
With the angle Al, the X-coordinate of 38c is defined by-
Xc = L2 GOS(Al)
As previously discussed, the lengths of lines 28 from cursorvertex 38c to the lower support structure vertices 44, 46 and 47 are also
known and are designated respectively as Ll, L2, and I-3. A conventional
orthogonal axes system has been defined with the origin positioned at vertex
46 and with vertex 47 located on the X axis at the point (1,0,0). The XZ
plane is defined by the three support structure vertices 44, 46, and 47.
There are, of course, several appropriate alternative mathematical solutions
to locating cursor vertex 38c in the Z~YZ coordinate system. For
illustration it is assumed that computer 16 has been programmed to perform
the following steps to ascertain the location of vertex 38c. However, the
present invention contemplates any derivation which properly locates the
vertices in question.
The law of cosines is again applied in the manner just described
to obtain L4, the length of the line between vertex 46 and point 60. The
ratio of L4/1 (1 being the arbitrarily chosen distance between vertices 449
46 and 47~ is multiplied by the coordinates of vertex 44 to establish the
coordinates of point 60:
L4 tO.5, 0, 0.866) = (0.5[L4~, 0, 0.866[L4])
Next, the equation of line 62 it derived by the conventional algebraic
point-slope technique knowing the coordinates OI point 60 and the slope of
line 62 The equation of line 62 is given by:
(Z Zl) = m(X - Xl)
where X1 and Z1 are given by point 60 as l0.5(L4), 0.866(L4)] and "m'~ is
defined as:
M = -l/Slope of L4 - -0.5/0.866 =-0.577
Next, the Z coordinate of vertex 38c may be calculated by solving
for the intersection of line 62 and the lîne x = Xc, where Xc is the X
coordinate of vertex 38c previously calculatedO Finally, the Y coordinate
of vertex 38c may be obtQined by:
yC2 = h2 - ZC2
where h = L2sin(A1) and Zc is the Z coordinate of vertex 38c previously
derived.
It i5 again noted that the above method of calculating the precise
location of CUrsQr vertices from known line lengths in relation to a known
support structure geometry merely illustrates one, of many, mathematical
approaches to achieve the same result. The mathematical relationships
necessary to properly program computer 16 are well known, even for more
complex non-symmetrical supporting structures and, therefore, will not be
considered in more detail herein.
As previously described, the twelve control lines are inter-
connected with torque motors 24 which, in turn, are variably 'programmed' by
the control computer 16 to apply a given tension to each of the lines.
Thus, as the cursor is moved within its supporting structure, the torque
motors 'reel-in' excess or slack line and 'play-out' additional line as
required to maintain the programmed line tension. The individual line
tensions are programmed by the computer in accordance with the forces
actually encountered by the slaved apparatus during use. Specifically, a
set of piezoelectric or similar force transducers (not shown) are mounted
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on the slaved apparatus and generate the force signals necessary for computer
processing. In this manner, cursor force feedback is provided which permits the
user to "feel" the tool forces substantially the same as if the procedure were
being performed directly with the tool or slaved apparatus in hand. Fhe relative
cursor-tool forces and/or mo-rement can be scaled as appropriate for the
procedure being performed. Thus, a given movement of the cursor may be scaled
upwardly to produce increased motion of the slaved tool or, importantlyt the
movement of the cursor may be scaled downwardly to proYide for the precise
motional control of, for example, delicate surgical instruments or the like.
Similarly, the respective line tensions programmed by the computer may be scaled
to provide the user with either an enhanced or attenuated force feedback
response. Thus, a critical surgical procedure requiring extremely precise and
'light' tool pressures can be scaled to provide the surgeon with an increased and
meaningful cursor force response.
In addition, the individual line tensions must be continuously
updated by the computer to reflect changes in the position of the cursor
within the support structure since the resultant force acting upon the
cursor, for any given set of individual line tensions, is a function of
the particular position of the cursor. This dependency relationship is
due to the fact that the relative angles between the cursor legs and the
support structure vertices vary according to the position of the cursor
within the support structure which results in a changing set of force
vectors acting upon the cursor legs by the respective tension lines.
Thus, where Q constant cursor force is desired, for example, when the
slaved apparatus is freely moving within a workspace without encountering
an object or workpiece, the computer must repeatedly recalculate the indi-
vidual line tensions as necessary to maintain this constant overall cursor
tension. In addition, it will be appreciated that changes in overall cursor
force due to corresponding changes in the resistance to movement of the slaved
apparatus, must similarly be adjusted by the computer to account for the actual
position of the cursor within its supporting structure. A set of mathematical
equations defining the relationships between line tensions7 cursor position, and
resulting cursor forces can be derived using conventional algegraic and geometric
principles in a manner similar to that outlined above. Computer 16 solves these
equations in accordance with the known cursor position and slaved apparatus
force data thereafter outputting the necessary control signals to torque motors
24.
The twelve tension line cursor support structure described herein
facilitates a wide range of cursor motions along the lineal as well as
torsional axes maintaining, at all times, a positive tension force on each
of the control lines and a corresponding positive or unidirectional force
output from each of the tension inducing torque motors 24. Thus, the
present arrangement completely avoids regions OI difficult or unstable
operation characterized by near zero or reversing cursor actuation forces.
It should be noted that the present controller is not limited to tetrahedral
line attachment and cursor support structures such as shown herein, but may
include a variety of other tension line geometries including, for example, a
three axes orthogonal structure wherein each of the attachment legs is
oriented at 90 degrees with respect to the adjacent legs. However, the
disclosed tetrahedral solution is preferred as offering significant
advantages relating to overall user accessibility of the cursor and,
importantly, in the simplicity of the mathematical solution to the vertex
position equations. Unlike the equations outlined above for locating each
of the four cursor vertices of the tetrahedral arrangement, the mathematical
relationships of the orthogonal cursor and supporting structure require the
solution of complex simultaneous equations. This is due to the fact
that the orthogonal cursor contains six vertices, each with two lines con-
nected thereto9 the position of which can not be uniquely determined
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without reference to line lengths interconnecting other cursor vertices. In any
event, the general twelve vertex, octahedral structure exhibits the highly
beneficial property ox full multi-axes control with a unidirectional actuating force
on each interconnecting actuation member ag previously discussed.
It will be understood that changes rnay be made in the details of
con3truceion9 arrangement and operation without departing from the spirit of
the invention especially as defined in the following claims. What is
claimed:
