Principles of superposition for controlling pinch motions by means of 
robot fingers with soft tips

Arimoto, Suguru; Tahara, Kenji; Yamaguchi, M.; Nguyen, Pham Thuc Anh; Han, Mo

doi:10.1017/s0263574700002939

Cited by 122 publications

(37 citation statements)

References 4 publications

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“…The decoupling of total force and total moment stabilization also supports the principle of superposition suggested originally in robotics (Arimoto et al 2000(Arimoto et al , 2001. According to this principle, some actions by manipulators may benefit from having separate controllers for components of the action such as gripping (force production) and rotation action (moment production).…”

Section: Multi-digit Synergies Stabilizing the Total Momentsupporting

confidence: 60%

Accurate production of time-varying patterns of the moment of force in multi-finger tasks

2006

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We investigated the production of time profiles of the total moment of force produced in isometric conditions by the four fingers of a hand. We hypothesized that these tasks would be associated with multi-finger synergies stabilizing the time profile of the total moment across trials but not necessarily stabilizing the time profile of the total force produced by the fingers. We also expected the multifinger synergies to prevent an increase in the moment variability with its magnitude. Seated subjects pressed on force sensors with the four fingers of the right hand and produced two time profiles of the total moment of force, starting from a certain pronation effort, leading to a similar supination effort, and back to the initial pronation effort. One of the profiles was a sequence of straight lines (M-Ramp) while the other was a smooth curve (M-Sine). The subjects showed an increase in the total force during each task. This was accompanied by an increase in the force produced by the fingers opposing the required direction of the total moment-antagonist fingers. Variability of the total force and of the total moment showed complex, non-monotonic changes with the magnitude of the force and moment, respectively. In both tasks, the subjects showed patterns of co-variation of commands to fingers that stabilized the required moment profile over trials. The time profile of the total force was stabilized to a lesser degree or not stabilized at all. The share of fingers with larger moment arms (index finger for pronation efforts and little finger for supination efforts) was higher when the fingers acted to produce moments in a required direction but not necessarily when they acted as antagonists. The results demonstrate the existence of multi-finger synergies stabilizing the combined rotational action. They fit a hypothesis that stabilization of rotational actions may be a default strategy conditioned by everyday experience. The data also suggest that the mechanical advantage hypothesis is valid for sets of effectors that act in the required direction but not for sets of effectors that act as antagonists.

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Section: Multi-digit Synergies Stabilizing the Total Momentsupporting

confidence: 60%

Accurate production of time-varying patterns of the moment of force in multi-finger tasks

2006

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“…To linearize the above equation we used the following experimentally established fact: humans control grasping force and rotational equilibrium of hand-held objects independently-the f G magnitude does not correlate with the moment that the f G generates (Shim et al 2003;Zatsiorsky and Latash 2004). This pattern of coordination exemplifies the principle of superposition suggested in robotics (Arimoto et al 2001). Following the principle of superposition for the handle shown in Fig.…”

Section: Discussionmentioning

confidence: 98%

Internal forces during object manipulation

2005

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Internal force is a set of contact forces that does not disturb object equilibrium. The elements of the internal force vector cancel each other and, hence, do not contribute to the resultant (manipulation) force acting on the object. The mathematical independence of the internal and manipulation forces allows for their independent (decoupled) control realized in robotic manipulators. To examine whether in humans internal force is coupled with the manipulation force and what grasping strategy the performers utilize, the subjects (n=6) were instructed to make cyclic arm movements with a customized handle. Six combinations of handle orientation and movement direction were tested. These involved: parallel manipulations (1) VV task (vertical orientation and vertical movement) and (2) HH task (horizontal orientation and horizontal movement); orthogonal manipulations (3) VH task (vertical orientation and horizontal movement) and (4) HV task (horizontal orientation and vertical movement); and diagonal manipulations (5) DV task (diagonal orientation and vertical movement) and (6) DH task (diagonal orientation and horizontal movement). Handle weight (from 3.8 to 13.8 N), and movement frequency (from 1 to 3 Hz) were systematically changed. The analysis was performed at the thumb-virtual finger level (VF, an imaginary finger that produces a wrench equal to the sum of wrenches produced by all the fingers). At this level, the forces of interest could be reduced to the internal force and internal moment. During the parallel manipulations, the internal (grip) force was coupled with the manipulation force (producing object acceleration) and the thumb-VF forces increased or decreased in phase: the thumb and VF worked in synchrony to grasp the object more strongly or more weakly. During the orthogonal manipulations, the thumb-VF forces changed out of phase: the plots of the internal force vs. object acceleration resembled an inverted letter V. The HV task was the only task where the relative phase (coupling) between the normal forces of the thumb and VF depended on oscillation frequency. During the diagonal manipulations, the coupling was different in the DV and DH tasks. A novel observation of substantial internal moments is described: the moments produced by the normal finger forces were counterbalanced by the moments produced by the tangential forces such that the resultant moments were close to zero. Implications of the findings for the notion of grasping synergies are discussed.

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“…Those studies have suggested that the control of two performance variables with the same set of effectors may be based on a principle of superposition (Arimoto et al 2001;Zatsiorsky et al 2004). According to this principle, separate controllers ensure co-variation within the same set of elemental variables that stabilizes each of the performance variables, and the effects of the two control signals sum up at the level of elemental variables.…”

Section: Stabilization Of Two Performance Variables By the Same Set Omentioning

confidence: 99%

Multi-muscle synergies in an unusual postural task: quick shear force production

2008

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We considered a hypothetical two-level hierarchy participating in the control of vertical posture. The framework of the uncontrolled manifold (UCM) hypothesis was used to explore the muscle groupings (M-modes) and multi-M-mode synergies involved in stabilization of a time profile of the shear force in the anterior-posterior direction. Standing subjects were asked to produce pulses of shear force into a target using visual feedback while trying to minimize the shift of the center of pressure (COP). Principal component analysis applied to integrated muscle activation indices identified three Mmodes. The composition of the M-modes was similar across subjects and the two directions of the shear force pulse. It differed from the composition of M-modes described in earlier studies of more natural actions associated with large COP shifts. Further, the trial-to-trial M-mode variance was partitioned into two components: one component that does not affect a particular performance variable (V UCM ), and its orthogonal component (V ORT ). We argued that there is a multi-M-mode synergy stabilizing this particular performance variable if V UCM is higher than V ORT . Overall, we found a multi-M-mode synergy stabilizing both shear force and COP coordinate. For the shear force, this synergy was strong for the backward force pulses and non significant for the forward pulses. An opposite result was found for the COP coordinate: the synergy was stronger for the forward force pulses. The study shows that M-mode composition can change in a task-specific way and that two different performance variables can be stabilized using the same set of elemental variables (Mmodes). The different dependences of the ΔV indices for the shear force and COP coordinate on the force pulse direction supports applicability of the principle of superposition (separate controllers for different performance variables) to the control of different mechanical variables in postural tasks. The M-mode composition allows a natural mechanical interpretation.

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Principles of superposition for controlling pinch motions by means of robot fingers with soft tips

Cited by 122 publications

References 4 publications

Accurate production of time-varying patterns of the moment of force in multi-finger tasks

Accurate production of time-varying patterns of the moment of force in multi-finger tasks

Internal forces during object manipulation

Multi-muscle synergies in an unusual postural task: quick shear force production

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