Note: Descriptions are shown in the official language in which they were submitted.
o 2182372
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MOTION CONTROL SYSTEMC
- The present invention relate~ to an apparatus
for controlling the motion of an object. In particular
it relates to motion control apparatus wherein forces
are generated by actuators such as electromagnetic
actuators having a piston and a cylinder and in which
relative motion is caused to happen between the piston
and the cylinder by means of electromagnetic force.
Examples of such electromagnetic rams are disclosed in
International Patent Application No. PCT/GB92/01277,
published as WO 93/016J.6.
The present invention also relates to a
corresponding method for controlling the motion of an
object or objects by means actuators such as for
example, electromagnetic actuators.
The present invention has applications in the
field of motion simulation. Motion simulators are now
used in, for example, flight simulators for training
pilots, an~ in arcade games based on activities such as
motor-cycle racing. In these examples, motion
simulation is generally f-nh~nred by the provision of
audio visual signals to the user ir. order to make the
experience of actual motion seem more realistic. Such
motion simulators are now known to the general public as
"virtual reality" ~--hin~c and are becoming more widely
available for recreational and educational uses. In
general motion simulators are known which utilize
hydraulic or pneumatic rams as the actuators providing
the n~ress~ry forc~s to move a user who may be in a
simulator cabin or on a simulator plane. More recently
it has been proposed by the inventor of the present
application to utilize ele~L~ ~ gn~tic actuators as the
thrust producers in motion simulation devices ~see, for
example, International Application PCT/GB92/01279,
published as Wo 93/01577 ) .
. ~ 2182372
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It is knl~wn for motion simulators, comprising
a set of actuators arranged between a base plane and a
simulator plane or cabin, to provide motion simulation
according to a predetPnmi ned program, wherein each
actuator operates according to predetPnmi nPd time
pPn~lPnt functions or to stored data in order to cause
a sequence of thrusts or moves to be applied to a
simulator cabin or simulator plane. In this way a user
on the simulator plane may experie~ce a "virtual reality
ride" around a well-known motor racing circuit or down a
well-known t~hqgg~ll run, for example. Such simulators
may be said to pro~ide "hard" simulation of a
predetPnrni nPd experience in the sense that the actuators
apply set sPtIupn~-pq of thrusts or moves to the simulator
plane or cabin irrespective of ally action on the part of
a user in a cabin or on a simulator plane. It is also
known for a user, or an externaL controller, to be able
to control the thrusts to be applied to the cabin or
simulator plane, by operation of, for exa~ple a steering
wheel or a joy-stick control system. Such simulators
are able to provide si 1;~ n of a non-predetprmi npd
experience, but may still be said to be providing "hard"
simulation since tlle motion or thrusts applied to the
cabin or simulator plane are still detPrminP~, albeit
contemporaneously, by a computer contro1 ~ni 1'."
responsive only to external ~ '-.
A particular example of motion simulator
employing a combination of the above two types of "hard"
simulation would be a flight simulator in which a user
in a cabin, the inside of which is intended to look and
feel like a cock pit, controls an "aeroplane" by
operating controls similar to those of a real aircraft.
Signals from these controls are processe~ and applied to
a set of actuators arranged to change the position and
orientation of the cock pit in order that the user
experiences the ef Fects of his own control of the plane
0 ~182372
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until such time as his actions, if carried out in an
aeroplane, would have resulted in an unrecoverable
crash. At such a time as this, the control of the
actuators may be ta~ken completely away from the user and
instead, the actuators may be controlled to simulate a
crash by running a predetPrr~i nPd sequence of moves .
Irrespective of whether the f light simulator according
to this example is in the first mode ~i.e. under the
user's control), or in the second mode ~i.e. performing
the predetPrminpd "crash" routine), the simulation may
be said to be "hard" on account of the fact that the
actuators are only responsive to externally driven
It is desired to provide motion simulators in
which signals provided to an actuator or to a set of
actuators are detPrminPd not only from external .ic
but also, for example, from L..~v~ L of a user in a
cabin or on a simulator plane. Signals determined as a
result of v L of the user may thus be provided to
the actuators in acdition to a predet~rmi nP-i sequence of
signals such that the user feels that his changes in
position are affecting the motion of the object whose
motion is being simulated. For example in a simulator
for simulating surfing on the sea, wherein a surf-board
is placed on a simollator plane, the actuators may be
provided with signals such that the simulator plane
moves as if under the action of waves, and in addition
to this, they may be provided with additional signals if
a "surfer" on the surf-board shifts his weight relative
to the surf-board, such that the motion of the surf-
board is affected by the v~ Ls of the surfer. Such
simulation may be referred to as "soft" simulation.
According to the present invention there is
provided apparatus for controlling the motion of a
member, comprising an actuator disposed between the
member and a ground level, and a control aLLa~ L
0 2182~72
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for providing control signals to the actuator whereby to
cause the actu~tor to generate thrust, characterised in
that said apparatus further comprises means for
monitoring cha:racteristics of the relative positions or
movements of tlle member and the ground level or the
forces between ground level, actuator and member, and
providing signals indicative of said characteristics,
and in that the control arrangement is responsive to
signals provided by the monitoring means and comprises
means for modi~ying or generating the control signals to
be provided to the actuator.
Preferred 'i Ls of the invention utilize
electromagnetic actuators and make use of the feature of
these that in ~ddition to converting electrical signals
to thrust, they may produce electrical signals directly
as a result of force being applied to them.
In the field of motion simulation outlined
above, apparatus according to an : ' of the
present invention in general comprises a plurality of
actuators disposed between a plane resting on the ground
and an object on which a user may "ride". The object on
which the user rides may be located on a plane which is
attnched to the actuators, or may be attached to the
actuators itself.
In order for motion simulation to be "soft" it
is generally necessary for the apparatus to include
means for monitoring characteristics of the position or
v~ of the member of a user on the member, although
it may be necessary also to monitor ~uLL-7~ i
characteristics of the ground plane in some
circumstances . In motion simul2tors ~ i ng a
preferred: ' i L of the apparatus according to the
present invention, use is preferably made of the fact
that currents are generated in the coils of an
electromagnetic actuator when there is relative movement
between the pis~on and the cylinder, and by monitoring
these currents, the extension or reduction of the
actuators as a ~esult of ~c L of the user may be
monitored without the need for further connections or
sensors to be mounted on the actuators. Alternatively,
however movemenl:s of the user may be detected by
1~ 218237~
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monitoring other characteristics, such as the angles
between the actuators, the lengths of the actuators, or
the rate of change of extension or reduction of the
length of the actuators. Also, .~ Ls of the user
may be detected more directly by attaching .c
sensors of any convenient type to the user or to the
member, or by any other convenient means.
Signals indicative of characteristics of the
position of movement of the member, having been obtained
by any chosen form of monitoring means, may be processed
by computer contro l means such as to provide contro l
signals to the actuator which are the sole control
signals to the act~ators. AlternatiYely, a
predetPrminPri sequence of control signals may be
modified as a result of signals received from the
monitoring means in order to "superimpose" the effects
of a users I ~, Ls on a prede~Prmi nPd ride. In either
such situation, the simulated motion may be said to be
"soft" .
As PYrl iinP~ above, motion simulators
Utili71ng -j ts of the present invention generally
include more than one electL, - ~ic ram, and may also
include other support means such as air springs. It is
not, however, nPcPqs~ry for there to be a plurality of
actuators, and a f~rther application of -'i Ls of
the present invention, in which a single actuator may
suffice, will be ou~tlined below.
It is well known that spring systems and
spring damper combinations can be modelled by computer
and that ideal spring and/or damper systems can be
designed in this w~y. However, when putting such
computer modelling into practice it is often the case
that design, ~ , i CP9 have to be made. In the past,
spring and damper combinations have been adjustable to
the extent that th~ damper characteristics may be
switched but again these are very crude systems when
~182372
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comp~red with the comput~r modelling which is possible.
The adv~nt of electromagnetic piston and cylinder
devices capable oE producing high thrusts has allowed
designers to produce any desir~d thrust characteristic
prof i le .
~ le now propose utilizing the controllable
aspect of a~ elec~romagnetic piston and cylinder device
to drive the pistcn forwards and backwards at rates
det~rrni n~d by the designer and between limit positions
also det~rmi n~ b~y the designer in order to simulate a
specific spring o~- combination of springs or in:~t1~n
of springs and daupers. The advantage of using an
~lectromagnetic r~lm system is that because the switching
of the coils whic}l causes the relative ~ b~twee~
the pisto~ and cylinder i already under computer
control, it is possible to feed new pL~L~ to the
~ r which wi:Ll 71ter the characteristics of the
piston and cylind~r device.
Piston and cylinder actuators controlled
according to some: i ~5 of the present invention
as set out above uay be made to act as "virtual
springs", "virtua3. dampers " or "virtual spring/damper
' inA1 l~n~ ti~li7ing terminology used in the field
of "virtual reality". A particular application of such
~ is in the field of suspension systems, such
a~ active s~Cp~n~L~n systems for vehicles. As explained
above, an ele_Ll, Lic actuator controlled according
to ~ '' ~ of the precent invention may be
controlled such t}lat it acts as a sprinq or a
combination of splings, a damper or a - inAtinn of
dampers, or a, inJ-rir~n of spri~gs and damperY. In
s~Cponci~n systems, the aim of controlling the motion
may be thought of as the reverse of that Ln motion
simulatlon, since it is generally desired to allow a
user a smooth a ride as possible in, for example,
situations whe~eill a vehicle is travelling over
` 218237~
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irregular terrain. The monitorinq of v L is thus
principally directed to that of a base plane or a set of
wheels, which may be considered to travel across the
"ground level", but monitoring means similar to those
described in relation to motion simulators may be used.
Other applications of the present invention
will become appare~t from a full description of
Ls of the invention.
r ~ rlts of the prese~t invention will now
be described with reference to the Ar- -nying figures
in which:
Figure 1 shows in diagrammatical form a motion
simulator of a kno~n type which may be controlled
according to an: 'i L of the present invention;
Figure 2 shows a perspective view of a
simulator Pni~-" such as that shown in Fig. l;
Figure 3 shows the two principal parts of an
electromagnetic actuator;
Figure 4 shows a piston suitable for use in an
alternative type of electromagnetic actuator;
Figures 5, 6 and 7 show alternative
arr In; c of an electromagnetiC actuator;
Flgure 8 shows a circuit for supplying current
to, and receiving current from, an electromagnetic
actuator;
Figure 9 shows, in diagrammatical form, an
-~i L of a motion control apparatus accordin~ to
the present invention;
Figure 10 shows, in diagrammatical form, an
active suspension system of a car, controlled according
to an 'i L of the present invention;
Referring to Figure 1, there is shown in
diagrammatical form a motion simulator to which an
_'i L of the motion control apparatus of the
present invention may be applied. A motion simulator
of this type, but for "hard" simulation was the subject
~182372
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of In~rnA~ nA1 Publication W094/10665, filed by the
applicant of the present application, the subject matter
of which is incorporated herein by reference.
As shown, there is a base plane 10, which may
rest on a floor or be otherwise stably supported, and a
simulator plane 40 on which may be mounted a capsule
motor-cycle, or surf-~oard, for example, (not shown)
that is to undergo simulated motion. The capsule may
represent a cabin, such as an aircraft cabin, in which a
user would stay during use in order to be subjected to
v~ L .
On the base plane 10 are mounted three
actuators 30 which are linearly ~yt~nrlihle
elect-, ~..e~ic ra~,s. ~iote that although no connections
to the actuators 3a are shown in Figure l, connections
would in general be required for electrical power and
signals, and possikly for fluid, as will be r~ lAin~d
later. The actuators are mounted in such a way that
each is free to rotate in direction A with one deqree of
freedom about a point 24 on the base plane 10. For
example, the actuators 30 may be mounted by means of
hinges 26 whose axes each lie in the base plane 10. In
general, the axes about which the acLue-Lu~ . are free to
rotate ( in the example, the axes of the hinges ) can be
extended so as to intersect with each other at points
forming a notional triangle 20 with sides 22 on the base
plane 10. This notional triangle 20 is in this
'i L an equilateral triangle. The axes of the
actuators 30 intersect with the axes about which they
are free to rotate at points 24 which are midpoints of
the sides 22 of the triangle 20 on the base plane 10.
These points 24 can be thought of as the coupling points
of the actuators 30. In this example, each coupling
point 24 is the midpoint of one of the sides 22 of the
triangle 20. They thus form a smaller triangle within
the triangle 20. On account of this, the axes of the
2~2372
_ 9 _
actuators 30 diverge from points on a common line
irrespective of their angular positions, this line
preferably being the line perpPnAic~ r to the base
plane, passing through the centroid of one or both of
the triangles.
Each act~lator 3 0 may be extended or shortened
in directions B by a length up to that of piston 32
which in general has a length less than or equal to the
length of the actuator, bu~ may be longer if it is
extendible in stages, with for example a telescopic
action or if the cylinder is open-ended and the piston
is allowed to move through it. The piston 32 may be
supported by a slide bearing 38, to further strengthen
the structure of the simulation ;~ni cn- The pistons
32 of the actuators 30 are each ~oined to a point of the
simulator plane 40 by means of a uniYersal bearing 36,
the three bearings forming a notional triangle 50. This
notional triangle S 0 is in this case an equilateral
triangle and is in the simulator plane 40. The two
notional triangles 20 and 50 may be of a similar size or
of different slzes, ~PpPnriing on the required extent of
the motion and the stability required. Generally
however the centre of mass of the capsule should be
aboYe the centroid of the triangle 50. In addition, the
centre of mass of the capsule should be kept, to a
required level of accuracy, above the centroid of the
-points at which the actuators are coupled to the base
plane. This condition may be maintained by suitable
choices of sizes a~d positions of the triangles 20 and
50, lengths of the actuators 30 and/or external control
of the types of v~ Ls that are caused by PYtF~n~linq
and shortening the actuators. (This external control
may be by physically preventing the actuators from
reaching angles outside a required range, or by computer
control of the lengths of the actuators according to
prP~Pt~rminpr1 algorithms or contemporaneous
1-- 2~82372
-- 10 --
calculations. ) The coupling points of the actuators 30
to the triangle 20 on the base plane 10 should thus be
separated sufficielltly from each ol;her for the triangle
20 to be sufficiently large to provide a means of
transferring the forces produced by the actuators to the
stable base plane 10.
Referring to Figure 2, there is shown a
perspective view o~ a simulator -- ~ni ~m such as that
shown diagrammatically in Figure 1.
Prior to explaining how a simulator ;Ini~
such as that shown in Figs. 1 and 2 may be controlled
according to the present invention, some types of
electromagnetic actuator suitable for use in such a
-hlni~ Will be clescribed with reference to Figures 3,
4, 5 and 6. Such ~.ctuators are the subject of
International Publi.cation WO 93/01646, filed by the
applicant of the present invention, the subject matter
of which is incorporated herein by reference.
Referring to Figure 3, there are shown the two
principal parts of an electromagnetic actuator, which
are, respectively, the cylinder 130 and the piston 135.
In this example, the cylinder 130 houses a plurality of
annular coils 131 which are separated from each other by
pole-piece rings 132. The piston 135 is of a suitable
size to slide within the central bore of the cylinder
130, and comprises a cylindrical steel sleeve 136 on the
exterior of which are mounted a plurality of segme~ted
windings 137. Currents in the coils 131 on the cylinder
may be proYided such that radial magnetic fields are
produced which interact with currents in the piston
coils 137, whose phase is controlled according to the
position of the piston and the required thrust
direction. Alternatively, currents flowing in the
piston coils 137 may produce radial magnetic fields
which interact with ~ILL~IlLS in the cylinder windings
131. A piston for an actuator such as this is shown in
237~
-- 11 --
Fig. 4, in which the piston comprises a steel core 140
provided with annular pole-pieces 141 and coils 142.
Alternative actuator arrA~ are
possible. Two further examples are shown in Figs. S and
6. In Fig. 5, there is shown, al~ actuator wherein a
cylinder 191 carries a plurality oE annular coils 192,
and wherein a piston 190 carries radially magnetised
ring-magnets 193. By applying suitable currents to the
coils 192, the pisl:on 190 may be made to experience an
electromagnetic fo3 ce such as to extend or shorten the
actuator. In Fig. 6, however, the steel cylinder 201
carries a series 03f ring magnets 202 which are radially
magnetised, while the piston 20~ carries segmented
coils 204, to which current may be applied to cause
electromagnetic force to be generated such as to extend
or shorten the actwator.
As is evident from the above electromagnetic
actuators for use in ~ -'i Ls of the present
invention may be 03- a variety of types, providing it is
possible to energise coils in either the piston or the
cylinder such as to generate electromagnetic forces
between the coils ~nd a magnetic system in the other one
of the piston and the cylinder. The ~--gnPri, system may
be a single p~3~-n~nt magnet, a series of p~r~-n,-nt
magnets, or one or more current-carrying coils.
While th~ principal function of the
electromagnetic actuators is to produce thrusts, it is
advantageous in embodiments of the present invention if
the actuators are adapted to perform the reverse
operation, this being the generation of currents in
coils in either the piston or cylinder as a result of
relative motion between the piston and the cylinder. ~y
virtue of this it is possible to detect slight changes
in the positional relatic~nchip of the piston and the
cylinder by monitoring currents in the coils. It is
further possible to utilize the currents in the coils to
, ~ ~lg2372
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recharge a battery, for example or to provide power for
use in the apparatus.
A further type of electromagnetic actuator
which is suitable for use in 'l Ls of the present
i~Lvention, will briefly be described with reference to
Figure 7. A full description of the unit, and in
particular its electromagnetic properties will not be
given as the basic unit may be o~ any of the types
referred to earlieJ~ or referred in our International
Patent Application W093/01646, or otherwise. In this
example, however t~1e principal features of the
electL - ~ic r~l include a cyli~der 230 having stator
coils 231, and pis1:on 232 having p~ n~nt magnets 233,
234 mounted thereoll. Additionally, the stator i nrl
conductive rings 2:15 at either end of the stator which
may be made of cop~er or ;,1 'ni for example, and act
electrical c~ch~nn~ to pr~vent violent impact by the
piston at th~ extremes of L,~ L~
The above! description refers pr;nrirJl Iy to
electromaLg~Letic ac~.uators 11~Lving a piston and a
cylinder, ho~ever in certain applications of the
invention it may be~ advantageous to utilize other types
of actuators, such as rotary torque a- LuaL~ s. rt is
thu$ not i n~on~lod that this inve~Ltion is limited to
~y~tem~ in which piston and cylinder a~ LuaLora are
or sy~tem~ in whic~ the actuators are
el~_L. ic.
In general, it is rL~c~c~-ry for an
elccLL -~ic ra~L to hav~ means to allow fluid to pass
out from the inside of the cylinder a~ it isl _ _~sed
by the ~. of the piston. In this example, ports
ar~ irLdicated as being connected to an air reservoir
which also in v.~o.~Les a~L air-pump. This may be used
to assist the elect~, Lic ram i~L providing large
thrusts, or by controlling the f luid pL~3~ to a
required level, it may be possible for a load to be
supported completely by fluid pressure, until such ti~Le
as the loa~ changes or moves. once such a chan~e alters
~ 2372
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the pressure from the load on the piston, the piston
will move due to the pressure in the piston from the air
reservoir/pump and due to the effect described above in
which relative motion of the piston and cylinder will
generate an electr~ ~nf~tc current, it will be possible
to detect the ~ v~ .L of the piston by virtue of the
monitoring of the detected currents, and it is also
envisaged that the currents generated by such relative
motion may be used to supply power to the system, or may
be stored f or use in the system or elsewhere .
A circuit for supplying current to and
monitoring and~or receiving current from an
electromagnetic actuator will briefly be explained with
reference to Figure 8.
The syste!l~ comprises an electromagnetic device
such as a ,~ i nF~d actuator/damper unit 310 which is
normally fed with power from an energy store 311 such as
a battery via a pow,~r switching device 312. In order to
provide the desired motion of the unit, the power
switching device 31Z is controlled by a controller 314
which pulse width modulates the supply to the
actuator/damper uni-t 310. The energy store 311 can be
re-charged, if appropriate, from an alternating supply
via a rectif ier 315 .
The actuator/damper unit 310 and drive
a~a~.-, L is, thus far, as descri~ed in our
~nternAtinn~l Patent Application WO93/01646.
When not being supplied with power to drive
the unit 310, it ma~ be used to generate electrical
power as a result of relative motioll of the piston and
cylinder of the unit 310. This power can be fed back to
the electrical store 311, if required. The controller
314 is therefore used to control a :Eurther power switch
320 for receiving current form nit 310 and feeding it
via a current transformer 312 and a rectifier 322 to the
store 311.
1-- 2~8237~
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Although the above described system
contemplates the d~mping action of the system being used
to replenish an energy store for activating the
actuator/damper unit, it could be used for other
purposes not nPc~ss~rily connected with the
actuator~damper unit 310. It is preferred to use it,
however, for some immediately useful purpose associated
with the damped action. In the case of an air-sprung
motion base, energy recovered from the unit 310 could be
used to drive a co~cpressor which charges an air
reservoir, for example. An ' ~';- L of the invention
will now be described with reference to Figure 7. This
shows motion control apparatus according to a preferred
'i ~ of the present invention, incorporating an
electromagnetic actuator which may be of any suitable
type as explained earlier, but in this example is of a
type with current carrying coils on the cylinder. A
computer control means supplies signals to a set of
pulse-width modulating switches which control the supply
oi' power to the coils in the cylinder in response to the
control signals rec~ived from the computer control
means. As a result of the supply of power to the coils,
the piston is suojected to thrusts qenerated as a result
of electromagnetic forces.
With the f eatures described aoove, the
apparatus would be capable of achieving "hard"
simulation. In order to allow the apparatus to provide
"soft" simulation, l:here is provided means for sensing
the relative positions of points on the cylinder and
piston, or other characteristics of the actuator parts,
such as the relative velocity of the piston with respect
to the cylinder. T~le position sensinq means provides
signals indicative of, in this example, the relative
positions of the piston and cylinder, to the computer
control means, which may then modify or generate control
signals to be sent to the switching means such that
- ~ 2182372
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forces with any descri~ed relatinnchip to the positional
relationship may be yLuduced.
The response det~rmi ne-1 by the computer and
control means may be detPrminP-I in a variety of ways.
Two simple applica~.ions of the above apparatus are as a
"virtual spring", or as a "virtual damper". These
illustrate manners in which the response may be
decided .
To simulate a convPnti~n~l spring it is
necessary for the restoring forces to be directly
proportional to the piston displacement over a
predetPrmi nPd distance . This is known as the
characteristic of the spring, and is summarised by the
equation
P = -kx,
where P is the restoring force, x is the displacement
from a reference point, and k is the spring constant or
spring rate. A chosen spring rate is thus entered by a
user, and is stored as data which is supplied to the
, ~Pr control means in order that a response to a
sensed positional relation~hi~ may be detPrmin~-d.
Similarly, to simulate a conventional damper,
it is nPCPCcAry for the restoring force ~ppncin J the
motion to be proportional to the rate of change of
displA~ L, i.e. ~he velocity of a moving point
relative to a reference point. This may be summarised
by the equation
P-- -qv,
where v is the velocity of the point and q is the
dampinq coef f icient .
A chosen damping coefficient is thus entered
by a user and is stored as data which is utilized by the
computer control means in order that a response to a
sensed velocity may be detPrn~i nPd .
The above two applications of the invention
may be superimposed, for example, if it desired to
218237~
-- 16 --
simulate a spring and a damper in parallel, by
calculating a restoring force according to the
equation .
P = - kx - qv.
The coefficients k and q may be chosen
int~ n~l~ntly, and may, for example, be chosen in
accordance with the dynamic mass of the object being
positioned in order to achieve critical damping.
Features of actual springs which are not
summarised by the principal linear relationship above
include springs reaching their elastic limit and springs
breaking. These features can also be imitated by a
virtual spring according to an _; of the present
invention. In order to simulate a spring reaching its
elastic limit, the restoring force is made to become
very large at a predetF-nmi n~d /1; cp~ L from a
reference point, su~h that the "spring" resists any
further stretching. On the other hand, in order
to simulate a spring breaking, the restoring force could
suddenly be reduced to zero by reducing the spring rate
to zero.
It will be clear that it is possible to
imitate a wide ranqe of spring or damper
characteristics, including many which are unattainable
with real springs alld dampers.
In some applications it would be an advantage
to use the apparatus as a spring whose characteristics
can ~e changed to suit with the dynamics of the load.
For example, it would be possible to tune the resonant
fLeyuen y of a system whose mass is not prede~rm;n-od or
is actually unknown, ~y altering the spring rate to
suit. Further, if t:he mass changes in time, perhaps as
a result of a controlled process, the force:distance
characteristic of the actuator can also be changed in
real time so as to achieve the desired resonance
characteristic .
0 ~1~237~
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As explained a~30ve, a particular application
of an ' 'i~ L of the preferred invention is in
virtual reality motion simulators. Referring again to
Figures 1 and 2, a surf-board may be placed on simulator
plane 40 in order to provide "virtual-reality surfi3ng".
In the absence of a user, the actuators 30 could be
supplied with signals such that the simulator plane 40
imitates the motion of a surf-board under the action of
waves, either when stationary or when moving across the
water. The actuators could be caused to produce regular
motion or a preder~rmi n~d sequence according to
prede~F-nmi n~r1 algorithms, or could he caused to produce
random or pseudo-ra3ldom motion within pre~i~fin~i3 limits,
by the control means (see Fig. 9).
A user cli333bing on hoard, or alternatively
onto the simulator plane 40 itself, would alter the
condition of the acl:uators and would continue to alter
this whenever he mo~ed his weight relative to the centre
of gravity of the simulator plane. On detection of such
changes in the cond~Ltion of the actuators, as monitored
by the sensing means (see Fig. 9 ), the control signals
to each actuator could be modified by ~h ingin~ the
algorithms by which they are controlled, or by
introducing damping co~ffi~ i~onts and spring rates, which
may be time-varying, for example, as well as ~rf-~-r3 L
on further changes in the position of the user on the
simulator plane . By virtue of such control, the user
will feel that his own v ts are affecting the
v~ L of the surf-board or simulator plane.
It will be noted that in motion contro}
systems having a pl~3rality of actuators, it may be
sufficient for the control signals to the actuators to
be supplied in-3.op~n~ntly, possibly by separate computer
control systems, in order to cause a predet~-nminf-d
sequence of moves such as, for example, to simulate the
effect of waves on the surfboard described above. If,
0 2182372
-- 18 --
however, it is desired that the motion control apparatus
is ~o superimpose "soft" simulatioll effects on the
prede~Prmin-d "hard" simulation by detecting and
responding to v, ~c of a user, it is generally
necessary for more than one sensor to monitor ~ Ls
of the user. In preferred embodiments, in which
movements of the user are monitored by monitoring
ef f ects on the actuators such as the generation of
currents in conduct:ive loops in the cylinders of the
actuators as a res~llt of relative motion between magnets
mounted on the pistons and the conductive loops in the
cylinders, it will generally be n~cF-s5:1ry for signals by
some or all of the actuators to be monitored by a
central computer me!ans in order for a realistic response
to be calculated. If, for example, a user moves his
weight towards one of the three actuators in the
simulator shown in Figs. 1 and 2, and away from the
other two actuators, the first actuator may generate a
"positive error signal" while the other two generate
"negative error signals". It will generally be
nf'C~SSAry to compare or analyse the three signals in
order to determine new control signals.
A further particular Arpl 1 cati nr~ of
Ls of the present invention is in the field of
ac~ive suspension for vehicles
Cars and other vehicles generally are provided
with a suspension system. A typical sUCp~nci~n system
for a car consists of a set of Ls equivalent to
a complex spring/da~mper combination, mounted between the
main body of the car and the wheels. By selecting
appropriate sprin~ and damper characteristics it is
possible to provide a suspension system offering two
particular advantages to the driver of the car. The
first of these is tllat the effect of sudden jolts, such
as those caused whe~l a wheel of the car encounters a
bump or a hole in tlle road, may be absorbed by the
21~237~
system such as to allow the driver of the car a more
comfortable ride. The second af these is that the
wheels of the car may remain in contact with the road
even in situations in which a car without a 5ll~p~ncinn
system would temporarily lose contact with the road,
such as may occur, for example, i~ one drives with
excessive speed o~er a ramp. This advantage is linked
to the ~irst advarLtage, and additionally allows for
better road-holding, leading to more effective steerlng
and ~reaking, and to decrease wear and tear of the
vehicle in general.
~ nown types of sllcp~ncinn systems for cars and
other vehicles include - - nir~l, hydraulic and
p~eumatic sllcpPncinn systems.
It is gen¢rally possible to ad~ust the spring
and damper characteristic of suspension systems of
vehicles. It may be n~ceas~ry to stop the car in order
to allow such adj~i c to be ~ade, but it is possible
to ad~ust the sllcpPncinn characteristics of some cars,
and in particular those for use in motor-racing, hy
means of controls within the car while the car is in
motion. It is thu~ possible to adjust the firmness of
the 51lcponc i nr~ in (~c~coLddnce with rhAn~Ji n~ road
conditions, such a~ to allow the car to be approximately
"critically dampedl' as it passes over varying terrain.
More recently, and in particular in the field
o~ motor-racing, a type of 5llcp~n~inr~ known as "active
S" r~ncinn" has be~ developed With active Sl-cr~ncinn,
the spring and daml~er characteri_tic5 of the 5l-cp~-ncinn
system are ad}usted ~ icllly in L~ ",6e to
detected changes ill driving conditions, such as changes
i~ steering, tiltillg of the car due to irr~gular or
cambered road surfaces, changes in the distribution
and/or amount of mass being carrled by the car, and
other changes. A t:ypical aim of all active s--c~.-ncinn
system i5 to alter the spring and damper characteristiC
.
0 ~2372
-- 20 --
C~ fln~ ly as t~le Yehicle moves over a surface haviAg
a~ variety of irre~3ularities, such a~ to in~Ain the
system iA a condi1:ion of critical damping, the spring
aQd damper charact:eristics beiAg set aAd altered in
L~ 0118_ to dc L~_ L.e1 changes iA driviQg conditions,
without the need for the driver to provide direct
~ '- to the suspension system. Known active
sllqp~n~ n systems iA motor-racing geAerally utilize a
hydr~7 ir~lly damped suspeAsion system iQ which the
hydraulic pressure or the volume cf water in the system
is alter~di as a result of the detection of changes in
driving conditioAs. Such changes may be detected by
means of straiA gauge3 attached to the wheel support
structure, or otherwise.
ReferriA~ now to Figure I0, a S--~r--nci~n
system of a car iq shown in dia~ ic form. The
diagra~ ir~lr~tos a front view of a car, and illustrates
OAly those features of relevaQce to an 09rl.-n-l ~nn of aA
active sll~pencirn ~ystem.
The car }~ody indicated by box 60 is liAlced to
a steering box 70 by steeriAg colu~Q 65, which
,~ i r~tes steeri Ag '~ provided to it by a
steering control means 62 to the s1:eeriAg box 70. These
m~ly be el~!ctronic, --lir-l, hydraulic or
p tr 9ignals, or may be other typ~s of signals.
Tl~ steeri7~g box 7CI is liA~ced to the front wheels 80 by
au~-.rLs 75 via axle~ 78, the ,u~po, Ls being movable in
to steeriDg - suc7~ as to alter the axis
of rotation of the wheels and thu~s to chaQge the
direction of the car. 8etween the body of the car 60
Qd the wheel suppcrts 75 are s~qr~"Qir~ system~ a5,
shown iQ this diagram a~ piston aQd cyliQder syst~ms.
The suspeAsion systems 85 are shown a boiAg controlled
by S-l~ponqi~n coAtrol systems 82. The S17qponq jnn
control systems 82 need not be withiA the car body 60.
2182372
Further there may be a single suspension control system
82 controlling all of the Sllcppncit~n systems, or there
may be a suspension control system for each sllcpPncil n
system or for each pair of suspension systems, for
example. Sensors of a variety of types, such as strain
gauges, may be mounted within the support structures 75
or elsewhere in order to detect changes in driving
conditions such as irregularities in the road surface
95. In the diagram, these sensors are indicated as
strain gauges 76 mounted on a leaf spring 77, the strain
gauges being connected electrically to the S-lcp~ncinn
contrDl means 82 by connection means which are not
shown .
The suspension systems 85 may initially be
controlled to act as spring/damper combinations having
predetenni nP~l spring/damper characteristics that
approximate to, for example critical damping for the car
moving at an averagi speed over an averagely bumpy road
while carrying an average load. The spring/damper
characteristics may be adjusted such as to provide
critical damping under changed conditions by providing
different signals from the suspension control systems
82, which may be hydraulic signals if the suspension
systems are hydraulic. In order for the sucppncinn to
be considered "active suspension" however, the
suspension systems 85 must be controlled in a manner
de~Pnmin~d at least partially from the results of the
detection of a characteristic of the driving conditions,
such as for example, irregularities in the surface over
which the wheels are travelling, or changes in the
steering direction of the wheels. The control of the
suspension systems 8~ may be the alteration of the
damping factor, whic,~ may ~e done for example at regular
intervals, or wherever a change above a threshold level
is detected, or continuously. Alternatively the control
may be of the length of the piston and cylinder
21~2372
-- 22 --
assembly. With control of this type, it may be possible
to maintain the car body at a prede~F~rmi n~ absolute
height irrespective of any holes or bumps ~nrollnrpred by
the wheels 80 by adjusting the length between the car
body 60 and the support stLU-.:LULt:s 75 in response to the
estimated size of each irregularity.
Other types of control, with alternative aims,
utilizing the concept of monitoring driving conditions
and controlling the suspension system accordingly, will
be apparent.
The applicability of the present invention to
the field of suspension systems alld to active 5llcpf~ncion
systems in particular, stems in part from the speed and
accuracy with which electromagnetic rams may be
controlled. It also stems in part from the fact that
suitably constructed actuators, preferably
electromagnetic, may serve not only as force ~ eL~,
but also as sensors of their own motion as a result of
other forces.
Referring again to Figure 10, if each
suspension system 85 contains an elect~, , Lic ram,
the support structures 75 or the wheels 80 are
rnn~ red to be on a notional "ground level", and the
car body 60 is cnnqi~i~red to be the member whose motion
it is intended to control. It will be noted that in
contrast to the field of motion simulation, in which the
int~nticn is to cause a member to move in relation to a
stably mounted groun~ plane, in the field of active
s--cp~nci nn it is gen~erally intended to decrease the
motion of a member such as a car body in spite of the
motion of a ground plane such as a wheel or support
structure, caused fo!r example by a wheel rolling over a
hole or a bump in the road.
Utili2ing suitably constructed electromagnetic
actuators in the suspension systems 85, characteristics
of the relative motion between the car body 60 and the
support structures 75 may be monitored by detecting
i~ 2~g23~ ?
-- 23 --
currents generated in the electromagnetic: ~ of
the pistons or cylinders of the electromagnetics rams.
Signals indicative of those generated currents may then
l~e 'supplied (by connection means not shown in ~igure 10 )
to the suspension control means 82 which are thus able
to alter the spring and damper characteristics or other
characteristics of the suspension systems 75 in
accordance with predet~nmi n~d functions of the slgnals
or in accordance with other data ~p~n~ nt on the
conditions of the electromagnetic rams. It is thus
possible to dispense with the i n~iop~n~ nr sensor systems
76, 77 while still allowing for sufficient monitoring of
driving conditions to enable active suspension to be
provided. In fact, by monitoring the signals from the
electromagnetic rams instead of those from; nA-~p~n~l~nt
sensors, it is genel-ally possible to monitor
characteristics more directly indicative of relative
motion between the car body 60 and the wheels 80 or
support structures 75, and thus to ~onitor relevant
characteristics of driving conditions more directly. It
is thus preferab}e that the "error signals" are produced
by the actuators themselves in this manner, but it is
envisaged that the ~rror signals may be produced to
other ways according to other ' ~i Ls of the
invention .
In addition to the f ields of motion simulation
and suspension systems, it is envisaged that; ' 'i Ls
of the present invention will have applications in many
otl1er fields. U~ 7ing the particular advantages of
electromagnetic actuators over most types of force
generator it is fore~eeable that ' _ 'i Ls of the
present invention will have applications, in particular,
in situations in which people and objects must be moved,
or stAhi 1 i 7~ despite v~-- L of their support, wherein
the control of motioll depends in some way on the
detection of characteristics within or outside the
2~8237~
-- 24 --
system. For example, if electromagnetic rams are used
as the force-generators in elevators, characteristics
such as changes in the total weight of the p~qs~n1~rs in
the lift as people enter and exit the lift could be
monitored, thus allowing the control signals to the rams
to be altered according to such changes. Transport of
delicate objects which may be damaged by jolts may be
effected very smoothly by use of suitably controlled
electromagnetic rams.
The particular adYantages of electromagnetic
actuators have been explained above. These stem in
particular from the feature that in addition to being
able to produce thrusts when energized by a suitable
electrical signal, they are also able to produce
electrical signals directly when sub~ected to forces
which cause relative motion between the - c of
the actuator. r -'i Ls of the present invention are
not limited to those utilizing electromagnetic
actuators, however. Other types of actuators, such as
for example ball-screw actuators may be used, having
means within or thereon with which to monitor
characteristics of the relative positions or ~,~ Ls
of the member and the ground level, or the forces
between the ground level, the actuator and the member,
in order to obtain slgnals from whicll to estimate or
calculate ~ Ls, or changes in the forces applied to
the system. It is foreseeable that sensors able to
monitor forces, i n~l~pen~ntly of monitoring any relative
motion between the actuator ~ ~ Ls, may be used.
