Abstract:
A method and a system for controlling a force feedback member able to interact with another member, including a local model for calculating a set point addressed to the force feedback member from a plurality of variables, and a remote model for estimating interactions and variables of the other member, with updating on receiving data from another remote system, and resynchronizer means able to send a resynchronization message to the other system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to transmission of force feedback over a long distance, in particular in the context of developing distributed virtual worlds and telepresence systems.  
           [0003]    2. Description of the Prior Art  
           [0004]    In the same way that digital video coding techniques are based on a knowledge of visual perception and voice recognition techniques are based on a knowledge of hearing, haptic techniques (from the Greek haptos: hand) are based on a knowledge of gestures.  
           [0005]    There are two sorts of fine gesture that can be executed by the hand: ballistic gestures, such as moving the hand toward a glass before taking hold of it, and gestures with touch feedback, such as moving the glass toward the mouth after taking hold of it and closing the clamp formed by the thumb and the fingers. The brain is then informed continuously of the force with which the hand is gripping the glass and of the weight of the glass, which depends on the quantity of liquid in it. The brain then reacts by giving the motor instruction to “grasp” the glass sufficiently tightly for it not to be dropped, but not too tightly, so as not to break it or expend energy uselessly.  
           [0006]    Ballistic gestures activate the motor reflex arc but they do not activate the touch feedback sensing reflex arc. Force feedback can be a visual representation of the space, but also a gestural map, that is to say a learned or innate mental representation hardwired into the brain and which automatically generates the sequence of motor instructions to the muscles of the shoulder, the arm and the hand to perform the ballistic gesture as a function of a particular mental representation of the space, in particular of the assumed hand-glass distance.  
           [0007]    For ballistic gestures, it is sufficient to transmit information on the gesture to the brain with a sampling frequency of 100 Hz. This means that if a sample of the signal is sent every 10 ms, the signal transmitted will contain all the information pertinent to the ballistic gesture.  
           [0008]    Gestures with touch feedback simultaneously activate the motor reflex arc and the sensing reflex arc. The brain closes the loop and in humans the complete cycle takes less than 1 ms. The bandwidth of the sensing neurons in the ends of the fingers, i.e. the maximum mechanical signal frequency that the neurons can detect and transmit to the brain, is greater than 500 Hz. To be able to code a fine gesture in a computer, the force feedback system used must itself have a high operating frequency, in accordance with Shannon&#39;s theorem a frequency of at least twice the bandwidth of the fingers.  
           [0009]    In practice, force feedback systems on a local machine typically operate at a frequency of 1 kHz and in a local closed loop, meaning that feedback is calculated and then applied to their motors and then perceived by the hand every {fraction (1/1000)} second. This avoids the effect known as the “electric toothbrush” effect: the instrument held in the hand must not give the impression of vibrating.  
           [0010]    The frequency of 1 kHz results from the following compromise: it must not be too low, if the tactile impression is to be reproduced finely, or too high, if the computer is to have sufficient time to calculate the feedback force that will represent the fine simulation of the gesture executed in the virtual mechanical world.  
           [0011]    If it is necessary to transmit via a telecommunication network fine gestures coded by the force feedback system and fine gestures with feedback, the problem is more complicated because of the generally much greater latency introduced by the network itself.  
           [0012]    Using the ISDN technology, the latency is 30 ms, using the ADSL technology it is of the order of 200 ms, and on the Internet it can be as much as 6 s or even lead to the message being purely and simply rejected. The ADSL and Internet latency varies because of the asynchronous nature of the networks. The frequency of 1 kHz is therefore much too high to be maintained if the closed loop includes a return trip via the network—the gesture is coded and then transmitted via the network, applied to a remote object, and feedback from the object is in turn coded and sent back via the network.  
           [0013]    A ballistic gesture can be transmitted with a time-delay of the order of 10 ms. Sight is a monodirectional sense: the eye is a kind of camera recording a scene and, ignoring a tolerance value, the brain can perceive the precise visual film with a slight time-delay without disturbing the execution of the gesture.  
           [0014]    On the other hand, a fine gesture with feedback requires a loop of less than one millisecond for the return trip to make the decision on the intensity of the force to be applied:  
           [0015]    sending of the instruction to the muscle via the motor sensing reflex arc,  
           [0016]    mechanical action of the hand on the glass,  
           [0017]    sensation at the ends of the fingers of touching the glass (increased contact pressure), and  
           [0018]    return of information to the brain via the tactile sensing reflex arc to enable the brain to decide to adjust the force applied to the “clamp”.  
           [0019]    A method known as the “wave transform”method for transmitting this kind of fine gesture is nevertheless described by John Wilson and Neville Hogan of MIT in “Algorithms for Network-Based Force Feedback”, Fourth PHANTOM Users Group Workshop (PUG 99). The method simulates the time-delay introduced by the network by means of an artificial viscosity that stabilizes the feedback loop: the greater the time-delay introduced by the network, the more viscous the system.  
           [0020]    The “wave transform” method transposes into the force/speed space the theory of passive quadripole networks with pure time-delay that is well known to the skilled person for electrical voltage/current parameters. The theory is used to calculate the incident and reflected electrical waves as a function of the characteristic impedance of the line. Transmission of the electrical signal is optimized if the line is terminated with the same characteristic impedance.  
           [0021]    Ohm&#39;s law U=Z×I is transposed into the mechanical space by the law F=Viscosity×Speed and the “wave transform” method consists of adapting a virtual pure time-delay line by assigning it a characteristic impedance (in reality a viscosity), which is that of the remote-controlled robot. The signal is transmitted in the form of its Z transform, S(z)=Σ(s(t)×e (2i×π×n×T) ) in which T is the fixed time-delay of the network. The greater the time-delay introduced by the network, the greater the artificial viscosity that must be introduced into the line to stabilize the distributed mechanical simulation of the fine gesture in a closed loop in the network.  
           [0022]    The gestural sensation is undoubtedly distorted, but transmission of the useful signal is optimized. This method was published following the Fourth Users Group Workshop (PUG99).  
           [0023]    The “wave transform” method requires a synchronous network, i.e. a network whose time-delay is fixed and known, for example an ISDN. It is based on the Z representation of sampled discrete signals whose period is equal to the known fixed time-delay of the network.  
           [0024]    It is therefore inapplicable to message-based asynchronous Internet, ATM or UMTS type networks, which are characterized by a variable transmission time-delay and by a rejection if the message is lost or takes too long to cross the network.  
           [0025]    The problem of the excessively fast timing of force feedback systems is exacerbated in asynchronous networks, for which:  
           [0026]    messages can be lost or rejected or fail to arrive if the acknowledgement is delayed for too long (TCP/IP),  
           [0027]    messages which reach the correct destination take a variable time to cross the network,  
           [0028]    they do not necessarily arrive in the order in which they were sent, and  
           [0029]    there is no common clock for the two machines accurate to within one millisecond.  
           [0030]    The invention proposes to remedy the drawbacks of the prior art systems.  
         SUMMARY OF THE INVENTION  
         [0031]    The invention proposes a control system for a force feedback member able to interact with another member, of the type with a time constant less than that associated with remote control, which system includes a local model for calculating a set point addressed to the force feedback member from a variable measured by the force feedback member, variables intrinsic to the force feedback member, an estimate of an external interaction with the force feedback member, and a state variable of the force feedback member, a remote model for estimating interactions and state variables of the other member with updating on receipt of data from another remote system, and resynchronizer means able to send a resynchronization message to the other system.  
           [0032]    Thus the behavior of the remote element is simulated locally.  
           [0033]    The system advantageously includes a phantom model for obtaining an estimate of state variables of the force feedback member and resynchronizing the estimate on reception of the resynchronization message. The phantom model is used to simulate locally the remote model of the remote control system.  
           [0034]    In one embodiment of the invention, the resynchronizer means include comparator means for comparing the estimate of state variables from the phantom model and state variables from the local model so that in the event of a difference exceeding a predetermined threshold the resynchronization means can send a resynchronization message to the phantom model and to the other system.  
           [0035]    In one embodiment of the invention, the system includes extrapolator means for processing a resynchronization message for updating the remote model received from the other system.  
           [0036]    The invention also proposes a system for controlling two force feedback members situated at a distance from each other. Each member is provided with a control system including a local model for calculating a set point addressed to the force feedback member from a variable measured by the force feedback member, variables intrinsic to the force feedback member, an estimate of an external interaction with the force feedback member, and a force feedback member status variable, a remote model for estimating interactions and state variables of the other member, with updating on reception of data received from another, remote system, and resynchronization means adapted to send a resynchronization message to the other system.  
           [0037]    The invention also proposes a method of controlling a force feedback member able to interact with another member, the method including:  
           [0038]    local modeling to obtain a set point sent to the force feedback member from a variable measured by the force feedback member, variables intrinsic to the force feedback member, an estimate of an external interaction with the force feedback member, and a state variable of the force feedback member;  
           [0039]    remote modeling of the interactions and the state variables of the other member with updating on receiving data from another remote system;  
           [0040]    generating a resynchronization message and sending it to said other system.  
           [0041]    The method advantageously includes phantom modeling of state variables of the force feedback member with resynchronization on receiving the resynchronization message.  
           [0042]    In one embodiment of the invention, at the time of resynchronization, the estimate of state variables from the phantom modeling and state variables from the local modeling are compared so that in the event of a difference exceeding a predetermined threshold a resynchronization message can be sent to the other system with a view to new phantom modeling.  
           [0043]    One embodiment of the invention includes extrapolation to process a resynchronization message from the other system and to update the remote modeling.  
           [0044]    The invention also provides a computer program including program code means for executing the steps of the method when said program runs on a computer.  
           [0045]    The invention also provides a medium capable of being read by a reader and storing program code means for executing the steps of the method when said program runs on a computer.  
           [0046]    The present invention applies with advantage to bidirectional systems, for example video games with control handgrips provided with force feedback actuators, and to robotized remote ultrasound scanning, which can be used in the field of obstetrics and for abdominal examinations.  
           [0047]    In the case of ultrasound scanning, the skin of the patient is generally coated with a gel to ensure correct transmission of the ultrasound. The ultrasound probe can be manipulated at a distance by an operator. Because of the presence of the gel, the components of force exerted by the patient on the probe can be considered as normal to the local surface of the skin. The probe has six degrees of freedom with force feedback with respect to three axes of a three-dimensional system of axes and torque feedback, also with respect to the three axes of a three-dimensional system of axes. The system can also apply to remote combat games, fencing games or industrial applications of the telemachining type.  
           [0048]    The present invention will be better understood and other advantages will become apparent on reading the following detailed description of a few embodiments, which description is given by way of non-limiting example only and illustrated by the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0049]    [0049]FIG. 1 is a diagrammatic view of a first embodiment of a system according to the invention.  
         [0050]    [0050]FIG. 2 shows a detail from FIG. 1.  
         [0051]    [0051]FIG. 3 shows evolution curves for some parameters of the system.  
         [0052]    [0052]FIG. 4 is a diagrammatic view of a second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0053]    As can be seen in FIG. 1, a game system in which players J 1  and J 2  compare their strength remotely—this kind of game is often referred to as an “iron arm” game—includes a handgrip P 1  for the player J 1  and a handgrip P 2  for the player J 2 . Each handgrip P 1 , P 2  is connected to an interface I 1 , I 2  including means for exerting a force on the handgrip P 1 , P 2 , for example an electric actuator, and means for measuring the force exerted by the player J 1 , J 2  on the handgrip P 1 , P 2 , for example a torque sensor or a strain gauge. The interface I 1 , I 2  also includes an acquisition card connected to the means for exercising a force and to the measuring means and able to exchange digital data with another digital system such as a computer.  
         [0054]    Each interface I 1 , I 2  is connected to a control system S 1 , S 2 . In the case shown here, the systems S 1  and S 2  are identical. Only the system S 1  is described. However, embodiments in which one of the two systems is of simplified structure compared to the other one can be envisaged.  
         [0055]    Generally speaking, the system S 1  can take the form of a personal computer, generally provided with at least one microprocessor, random access memory and read-only memory, a communication bus, input and output ports and one or more programs stored in memory and executed by the microprocessor.  
         [0056]    The system S 1  is connected on the one hand to the interface I 1 , for example by an RS 232 bus, and to the system S 2  by a communication network  3 , which can be a synchronous network (for example an ISDN) or an asynchronous network (for example an ATM or UMTS network or a TCP/IP network like the Internet). The system S 1  is located near the player J 1 , for example in the same room. The system S 2  is at a distance from the system S 1  from a few meters to a few thousand kilometers. In other words, the system S 1 , the interface I 1 , the handgrip P 1  and the player J 1  can be described as “local” and the system S 2 , the interface I 2 , the handgrip P 2  and the player J 2  can be described as “remote”.  
         [0057]    To be more precise, the system S 1  includes a local model ML 1  able to send the interface I 1  a set point F e  and to receive from said interface I 1  a variable measured by the interface I 1 , for example the position X of the handgrip P 1 . The set point can be a force or torque variable. The system S 1  includes a remote model MD 2  adapted to estimate a state of the local model ML 2  of the system S 2 . The remote model MD 2  of the system S 1  can receive data from the system S 2  and from the local model ML 1  and can send data to the local model ML 1 . To be more precise, the system S 1  includes an extrapolator EXT 2  receiving data from the system S 2  via the communication network  3  in order to process a resynchronization message from the system S 2  and transmit update data to the remote model MD 2  as a function of the resynchronization message received last.  
         [0058]    The system S 1  includes a screen E 1  connected to the local model ML 1  to display data from the local model ML 1 , for example a curve tracing the evolution of the forces exerted on and the positions of the handgrips P 1  and P 2 .  
         [0059]    The system S 1  includes a resynchronizer R 1  receiving data from the local model ML 1  and adapted to send output data to the system S 2 , in particular to the extrapolator EXT 1  of the system S 2 . The resynchronizer R 1  can handle data preparation for sending the data in the form of a resynchronization message that can include a time/date, the position X of the handgrip P 1 , the force F exerted on the handgrip P 1  at said time/date and the force exerted on the handgrip P 1  at an earlier time/date.  
         [0060]    The system S 1  further includes a phantom model MF 1  which also receives the resynchronization messages from the resynchronizer R 1  of the system S 1  and estimates state variables of the interface I 1  from the resynchronization messages set by the resynchronizer R 1  and received by the system S 2 . In other words, the phantom model MF 1  produces an estimate based on the same data as that received by the remote model MD 1  of the system S 2 . Thus the phantom model MF 1  is used to model the variables of the interface I 1  as modeled by the system S 2 .  
         [0061]    The output of the phantom model MF 1  is connected to the resynchronizer R 1  which compares the estimate of the state variables from the phantom model MF 1  and the state variables from the local model ML 1 . If the difference exceeds a predetermined threshold, the resynchronizer R 1  sends a resynchronization message to the phantom model MF 1  and to the extrapolator EXT 1  of the system S 2 . Thus the volume of data exchanged between the systems S 1  and S 2  is relatively small because a resynchronization message is sent only if one of the two systems S 1 , S 2  estimates that the other system S 2 , S 1  is no longer able to estimate the variables correctly.  
         [0062]    How the system works is clear from FIG. 2. For the player J 1 , the state vector X breaks down into three parts: a variable part X e  at the interface with the handgrip P 1 , a variable part X m  internal to the mechanical model of the player J 1 , and an interaction variable X i  at the interface with the other player. Similarly, the associated force or torque variable F breaks down into: a force F e  exerted by the player J 1  on the handgrip P 1 , a force F m  exerted by gravity, other objects, or any other players, and the force F i  exerted by the player J 1  on the player J 2 . In a similar manner, the state vector Y of the player J 2  breaks down into parts Y′ e , Y′ m  and Y′ i  and the associated torque force vector G breaks down into parts G′ e , G′ m  and G′ i . The two players J 1  and J 2  are in virtual contact. Thus X i =Y i . The law of action and reaction then yields: F i +G′ i =0.  
         [0063]    On each time increment, the interface I 1  captures the position X e   n  and transmits it to the local model ML 1 . The interface I 1  receives the set point force F e   n  from the local model ML 1  and uses the force feedback force −Fe e   n  to control its actuator(s) Similarly, the interface I 2  captures the position Y′ e   n  and transmits it to the local model ML 2  and receives the force G′ e   n  from the local model ML 2  and controls its actuator(s) with the force feedback force −G e   n .  
         [0064]    At the beginning of the time period n+1 the local model ML 1  receives the position X e   n+1  from the interface I 1 , the interaction estimate {tilde over (G)} i   n+1  from the remote model MD 2  and the prestored intrinsic variables F m   n+1 . The local model ML 1  calculates the force exerted by the player J 1  on the player J 2 :  
         F i   n+1 ={tilde over (G)}i n+1    
         [0065]    and the force exerted by the player J 1  on the handgrip P 1 :  
           F   e   n+1   B   ee−1{X   e   n+1   −X   e   n   −A   e   X   N   −B   em   F   m   n+1   +B   ei    {tilde over (G)}   i   +1 },  
         [0066]    the matrices A and B being those for the evolution of the player J 1  with X=AX+BF. The local model ML 1  then calculates:  
         X     n   +   1       m   ,   i       =       X   n     m   ,   i       +       A     m   ,   i            X   n       +       B     m   ,   i            [           F     n   +   1     e               F     n   +   1     m               -       G   ~       n   +   1               ]                               
 
         [0067]    The local model ML 1  sends X n+1  and F n+1  to the resynchronizer R 1 , the set point −F e   n+1  to the interface I 1  and the position variable X i   n+1  to the remote model MD 2 .  
         [0068]    In the event that it does not receive a message from the resynchronizer R 1 , the phantom model MF 1  calculates  {circumflex over (F)}   n+1 = {circumflex over (F)}   n +K 1 , K 1  being provided by the system S 2 , and the position estimate  {circumflex over (X)}   n+1 =(I+A) {circumflex over (X)}   n +B {circumflex over (F)}   n+1 , in other words the mechanical state of the player J 1  such as it can be predicted by the system S 2 . Here I is the identity matrix.  
         [0069]    When the phantom model MF 1  receives a resynchronization message M n ={n, {overscore (X)} n , {overscore (F)} n  and {overscore (F)} n−1 } from the resynchronizer R 1 , it carries out the following resynchronization: {circumflex over (X)} n ={overscore (X)} n , {circumflex over (F)} n ={overscore (F)} n and K 1 ={overscore (F)} n −{overscore (F)} n−1 .  
         [0070]    In each time increment n the resynchronizer R 1  receives the position variable X n  and the force variable F n  and F n+1  from the local model ML1 and the estimate  {circumflex over (X)}   n  from the phantom model MF 1 . It compares the absolute value of the difference between the position variable X n  and the estimate  {circumflex over (X)}   n , to a predetermined threshold and does nothing if said absolute value is below said threshold. If said absolute value is not below said threshold, it composes a resynchronization message M n ={n, X n , F n , F n−1 }. The resynchronizer R 1  sends the resynchronization message M n , to the phantom model MF 1  so that it resynchronizes itself immediately and to the remote model MD 1  via the extrapolator EXT 1  of the system S 2  so that it resynchronizes itself as soon as possible.  
         [0071]    The extrapolator EXT 2  of the system S 1  is used for synchronization. The message M p ={p, Y p , G p , G p−1 } sent by the resynchronizer R 2  of the system S 2  reaches the system S 1  at a time from n to n+1. However, the message M p  is stamped with the time/date p from the system S 2 . The extrapolator EXT 2  calculates K 2 =G p −G p−1  and resynchronizes the remote model MD 2  as follows: {overscore (G)} p =G p  and {overscore (Y)} p =Y p ,and then at the subsequent times, and regardless of the outcome: j=p, . . . , n, {overscore (G)} j+1 ={overscore (G)} j +K 2  and {overscore (Y)} j+1 ={overscore (Y)} j +C{overscore (Y)} j +D{overscore (G)} j+1 , C and D being the matrices equivalent to the matrices A and B for the player J 2 . The extrapolator EXT 2  sends the remote model MD 2  the resynchronization result {overscore (Y)} n+1 ,{overscore (G)} n+1  and K 2 .  
         [0072]    The remote model MD 2  of the system S 1  resynchronizes itself on receiving a message from the extrapolator EXT 2 , taking the values supplied by said extrapolator EXT 2 :  
         {tilde over (G)} n+1 ={overscore (G)} n+1 ,{tilde over (Y)} n+1 ={overscore (Y)} n+1  and {tilde over (K)} 2 =K 2    
         [0073]    When not receiving any such message, and on each time increment, the remote model MD 2  receives the position variable X i   n+1  from the local model ML 1  and performs a predictive calculation:  
         {tilde over (G)} e′,m′   n+1 ={tilde over (G)} e′,m′   n {tilde over (K)} e′,m′ 2  
           {tilde over (G)}   i   n+1   =D   ii−1   {X   i   n+1   −{tilde over (Y)}   i   n   −C{tilde over (Y)}   i   n   −D   e′   G   e′   n+1   −D   m′   G   m′   n+1 } 
         
       {tilde over (Y)} 
       e′,m′ 
       n+1 
       ={tilde over (Y)} 
       e′,m′ 
       n 
       +C 
       e′,m′ 
       {tilde over (Y)} 
       n 
       +D 
       e′,m′ 
       {tilde over (G)} 
       n+1  
     
         {tilde over (Y)} i   n+1   =X   i   n+1    
         [0074]    The remote model MD 2  sends the local model ML 1  the position variable prediction  {tilde over (G)}   n+1  relating to the player J 2 .  
         [0075]    The extrapolator EXT 2  preferably effects a bevel resynchronization which smoothes the changes. One example of such resynchronization is shown in the FIG. 3 curves. Instead of changing the estimate of the position variable Y suddenly to the variable {overscore (Y)}as calculated by the extrapolator EXT 2  in the manner explained above, the resynchronization is effected in four steps between times n and n+4, as follows:  
         k=| {tilde over (Y)}   n+1 −{overscore (Y)} n+ |/threshold+1.  
         If k=1, then  {tilde over (Y)}   n+1 :={overscore (Y)} n+1 .  
         If not, j=n,  
           {overscore (G)}   j+1   ={overscore (G)}   j   +K 2  
         
       {overscore (Y)} 
       j+1 
       = 
       j 
       +C{overscore (Y)} 
       j 
       +D{overscore (G)} 
       j+1  
     
         
       {tilde over (Y)} 
       j+1 
       :={tilde over (Y)} 
       j 
       +C{tilde over (Y)} 
       j 
         130  D{overscore (G)} 
       j+1  
     
           {tilde over (Y)}   j+1 =( {overscore (Y)}   j+1 +( K− 1) {tilde over (Y)}   j+1 )/ K    
         j:=j+1  
         [0076]    If k is greater than 2, then k:=k−1  
         [0077]    Otherwise the loop is left and Y j+1 ={overscore (Y)} j+1 . The bevel resynchronization enables the system to operate more smoothly, which is better appreciated by users and entails fewer mechanical constraints.  
         [0078]    More generally, the phantom model MF 1  receives the same data as the remote model MD 1  of the other system and can effect the same simulation as said other system. In other words, a search is conducted to find out what the other system does not know for the purposes of resynchronization. The resynchronizer works blind relative to the other system and enables simulation to continue in the absence of pertinent data transmitted by a resynchronization message from the other system. Especially in the case of bevel resynchronization, the extrapolator EXT 2  takes account of movement as measured by the other system during the transmission time-delay caused by the communication network. In a simplified variant, it is perfectly conceivable for either or both systems to have no phantom model. A number of systems greater than two can equally be made to work together.  
         [0079]    The local models represent the mechanical models of the two users. The remote models represent a remote replication of the local mechanical models which is necessarily approximate because of the time-delays on transmitting the states of the local models via the communication network. The phantom models represent an approximate local copy of the remote model. The remote models and the phantom models both work in predictor-corrector mode. The extrapolators extrapolate messages received with a certain time-delay to resynchronize the remote models to the clock value of the other system. The resynchronizers evaluate the necessity to launch a resynchronization message into the communication network as soon as there is too great a difference between the local models and the local witness predictive phantom models of the remote predictive models. The resynchronizers limit the number of messages sent via the communication network to avoid congestion on the network. Within a system, information can be exchanged at the rate of 1 kHz. Between the systems, and therefore via the communication network, messages are exchanged if one of the resynchronizers considers it to be necessary.  
         [0080]    [0080]FIG. 4 shows an embodiment of the invention intended for ultrasound scanning. A control system S 1  is installed in an establishment that does not specialize in obstetrics, for example in an establishment of a small town or in a vehicle serving rural areas. The system S 2  is installed in a specialized hospital establishment in which highly qualified operators are available to perform the ultrasound scanning operations, for example a regional or teaching hospital. A patient J 3  lies on a bed or a table T. An ultrasound scanning probe SE is in contact with their abdomen. A panel TR for adjusting parameters of the probe SE is installed nearby. The probe SE is connected to the system S 1  and transmits ultrasound scanning image data to said system S 1 ; it also exchanges data relating to the position of and to the actions exerted by the system S 1 . To clarify the drawing, the support of the probe SE is not shown; it can be an articulated arm. Nevertheless, it is to be understood that this support provides movement in space with several degrees of freedom, in general at least six degrees of freedom, so that a suitable position in contact with the abdomen of the patient J 3  can be adopted. A microphone MI 3  and a loudspeaker HP 3  are connected to the system S 1  to enable the patient to converse with the remote operator. A video camera CA 3  points toward the patient J 3  and a video screen EV 3  enables the patient to see either the remote operator or the ultrasound scanning images. The video camera CA 3  and the video screen EV 3  are also connected to the system S 1 . In addition to the items described with reference to FIGS. 1 and 2, the systems S 1  and S 2  each include a multiplexer-demultiplexer DM 1  and DM 2  for transmitting data via the network  3 , which can be an ADSL network, for example.  
         [0081]    The operator J 4  of the system S 2 , who can be a doctor specializing in ultrasound scanning, manipulates a handgrip P 3  whose position in space is replicated by the probe SE. The handgrip P 3  is connected to an articulated arm BA which is in turn connected to an interface I 3  which is of the same kind as the interfaces I 1  and I 2  described above and includes one or more actuators and one or more position sensors and force sensors. The effect can be measured by measuring an actuator energy parameter, for example the current drawn, or by means of a strain gauge. The interface I 3  is connected to the system S 2 .  
         [0082]    A video camera CA 4  points toward the operator J 4  and the pictures it generates can be displayed on the screen EV 3 . A microphone MI 4  and a loudspeaker HP 4  enable the operator J 4  to converse with the patient J 3 . These items are connected to the system S 2 . A large video screen EV 4  displays a plurality of images simultaneously, for example an ultrasound scanning image, an image of the face of the patient J 3  and an image showing the position of the probe SE on the abdomen of the patient.