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Haptic Teaching using Opposite Force Presentation

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                                             Haptic Teaching                                                                                                                                                                             This poster is associated
                                                                                                                                                                                                                                         with a Hands-On Demo
                                     using Opposite Force Presentation
                                             Satoshi Saga* Naoki Kawakami* Susumu Tachi*
                                              (*) The University of Tokyo, Japan
                         E-mail: satoshi_saga@ipc.i.u-tokyo.ac.jp,{kawakami,tachi}@star.t.u-tokyo.ac.jp

1. Abstract
                                                            devices
    We propose a haptic teaching system that uses haptic devices to teach hand skills.
                                             pencil-
  Specifically, we chose some tasks with pencil-like devices and examined how to
           expert’
  teach an expert’s hand skills. We proposed a new haptic teaching method, in which
                                                                                     tries
  the haptic device produces force that is in the opposite in direction. The trainee tries
                                                               ‘‘proactively’’
  to cancel the force and consequently, necessary force is ‘‘proactively’’ generated.
                                ‘‘proactiveness’’
  Our hypothesis is that this ‘‘proactiveness’’ is essential for haptic teaching. We
  made a prototype system and compared our methods with existing teaching        teaching
  methods.
                                                                                                                                                                      Fig.1: Existing methods
2. Description
   Let FE and FT be output force of the expert and the trainee. ‘‘Proactive’’
                                                                  ‘‘Proactive’’
                                                                                                                                                      Expert’s Phase                                                                     Trainee’s Phase
                                                                                                                                            Haptic Device                                    Haptic Device
                                                           necessary
  operation means that a trainee outputs the force that is necessary for operation and
  equal to the force FE. We propose the following methods to realize this situation.                                                                                       Expert            Inverse                                                       Trainee
                                                                                                                                    Reaction                                                 Internal
                                                                                                                                    Force                                                    Force
Expert’
Expert’s Phase: The expert’s model motion and force FE are recorded. The
                    expert’                                                                                                                  Freact
                                                             measuring
  haptic device with a tool attached at the tip is used as a measuring machine.                                                                                                                                  Finv                                      FT
                                                                                                                                                                           FE Manipulate                                                                             Manipulate
                                                                                                                                                                                Force                                                                               Force
Trainee’
Trainee’s Phase: Following two methods are combined.
                                                                                                                                                                            Trajectory                                                                     Virtual Trajectory

  A) Opposite presentation of expert’s force along trajectory (Finv)                                                                                                                         Virtual Fixtures                                              Fvf
                                                                 amplitude
    • The haptic device generates the force that has the same amplitude of the expert,
                                                                                                                                                                     Fig.2: Proposed method
      but in opposite direction. The trainee tries to cancel the force and
                      direction.             tries
                                                 “proactively”
      consequently, necessary internal force is “proactively” generated.
                 F
           FT = -Finv = FE
                                                                                                                                                                                                                                  Normal & Vertical
  B) The utilization of Virtual Fixtures [2] orthogonal to the trajectory (Fvf )                                                                                                                                                  to the trajectory
                                                    (figure2
     • Information of the expert’s motion is given (figure2), and the pathway is used                                                                                                                   Normal & Horizontal
       as a ruler by using Virtual Fixtures technique.                                                                                                                                                                                                                        Tangential
                                                                                                                                                                                                        to the trajectory
                                                                                                                                                                                                                                                                              to the trajectory
           Fvf = - k (xT - xE) 3                                                                                                                                                                                                      Trajectory

           Fdisp = Finv + Fvf

3. Experiment / Result                                                                          Fig.3: System overview                                                                                                          Fig.4: Separating force
                                                                   method,
      The proposed method was compared with the following existing method,
  through an experiment of letter writing tasks.                                                                                                Correlation of Force History
                                                                                                                         0.7
                                                                                                                                                                      Existing Method
                                                                                                                                                                      Proposed Method
                                                                                          Correlation of Force History




                                                                                                                         0.6
                       Slaved-
  • [Existing method] (Slaved-Tracking Mode)
                                          Mode)
      Passively               expert’
      Passively following the expert’s positional information as presented by the                                        0.5
      haptic device.                                                                                                     0.4
                                                                                                                                                                                                                                                  NormalVerticalForce Error
                                                                                                                                                                                                                                0.75
                                                                       reversed”
      We recorded force history data while subjects wrote “mirror reversed” Greek          0.3                                                                                                                                                                                            proposed
                                                                                                                                                                                                                                                                                          exisiting
                                                                   estimate
  letters with both the proposed and existing methods. First, to estimate the effect of    0.2
                                                                                                                                                                                                                                 0.7
                                                                                                                                                                                                         Force Error(N/frame)




                                                                 subject’      expert’
  these methods, we calculate these correlations between the subject’s and expert’s                                                                                                                                             0.65
                                                                                           0.1
                                                               normal
  history data. Three components of the force (tangential, normal vertical, normal
  horizontal part(Fig.4)) were separately evaluated. The result is shown in Fig.5.           0
                                                                                                                                            Tangent           Normal & V    Normal & H
                                                                                                                                                                                                                                 0.6

  Through comparison, we found our method can transmit tangential and normal                                                                          Each Force Direction
                                                                                                                                                                                                                                0.55
  horizontal force history to the trainee better than the existing method.              Fig.5:                                             Correlations of force history
                                                                                                                                                                                                                                 0.5

                                                                       and
      Second, we examine the learning effect of our proposed method and existing                                                                          TangentForce Error                                                    0.45
  method by recording force history data between the iteration of practices. The result                                             0.36
                                                                                                                                              proposed
                                                                                                                                                                                                                                    0         1        2        3         4          5         6         7
                                                                                                                                                                                                                                                   Number of Trial(times)
                                                                   learning
  is shown in Fig6. We found our method achieves some result in learning tangential                                                 0.35      exisiting

  force and normal horizontal force.                                                                                                0.34
                                                                                                             Force Error(N/frame)




                                                                                                                                                                                                                                              NormalHorizontalForce Error
                                                                                                                                    0.33                                                                                0.44
                                                                                                                                                                                                                                                                                         proposed
                                                                                                                                    0.32                                                                                                                                                 exisiting
                                                                                                                                                                                                                        0.42

4. References
                                                                                                                                                                                                Force Error(N/frame)




                                                                                                                                    0.31
                                                                                                                                                                                                                                0.4
                                                                                                                                     0.3
                                               Psychol.                 477-
[1] Gibson J.J.: Observations on active touch. Psychol. Rev, 69: pages 477-491, 1962.                                                                                                                                   0.38
                                                                                                                                    0.29
[2] L. Rosenberg. Virtual fixtures: Perceptual tools for telerobotic manipulation. In
                                                                                                                                    0.28                                                                                0.36
                                 Int’ Symposium,          76–
  Proc. of IEEE Virtual Reality Int’l. Symposium, pages 76–82, 1993.
                    Nakao,                Oyama,
[3] Y. Kuroda, M. Nakao, T. Kuroda, H. Oyama, M. Komori and T. Matsuda,                                                             0.27
                                                                                                                                        0       1         2     3      4    5     6      7                              0.34

  “Interaction Model between Elastic Objects for Accurate Haptic Display”,                                                                             Number of Trial(times)
                                                                     Display”                                                                                                                                           0.32
                                                      Tele-          (ICAT),
  International Conference of Artificial Reality and Tele-Existence (ICAT), pages.
                                                                                                                                                                                                                                0.3
  148-
  148-153, 2003                                                                                                                                                                                                                    0      1        2        3         4          5         6         7
                                                                                                                                                                                                                                                  Number of Trial(times)
                  Burdet,
[4] C. L. Teo, E. Burdet, and H. P. Lim. A robotic teacher of Chinese handwriting. In
                                                              Environment
  Proc. of 10th Symposium on Haptic Interfaces for Virtual Environment and
                 Systems,       335–
  Teleoperator Systems, pages 335–341, 2002.
                                                                                                                                                               Fig.6: Learning Curves of Each Force

				
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