Constraints for joint angle control of the human arm

Cruse, Holk

doi:10.1007/bf00320483

Cited by 189 publications

(49 citation statements)

References 5 publications

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“…3) shows that there is not a full agreement between both types of cost functions. Nevertheless, the difference is small enough that the results can be considered to support the assumption that the psychophysically measured comfort functions provide a measure for the hypothetical cost functions postulated to explain the targeting movement (Cruse 1986). The result that the hypothetical cost functions depend on the physiological costs further supports the speculation that the physiological costs and the psychophysically measured comfort functions are also related.…”

Section: Discussionmentioning

confidence: 54%

“…The aim of the current investigation was to look for measurable values corresponding to the hypothetical cost functions which were postulated earlier for the control of the redundant arm (Cruse 1986;Cruse and Briiwer 1987). The first question investigated was whether the choice of the arm position depends solely on the values of the joint angles or also on the length of the limbs.…”

Section: Discussionmentioning

confidence: 99%

“…As described in two earlier papers (Cruse 1986, Cruse andBriiwer 1987), the movement of the arm is restricted to the horizontal plane and the three joints at shoulder, elbow and wrist are free to move. To measure the values of the joint angles the arm of the subject was laid on an artificial arm having three joints which was free to glide over a horizontal plane.…”

Section: Methodsmentioning

confidence: 99%

“…The question arises of how the control system selects one of the infinite number of possible positions when trying to reach a given point. In an earlier paper considering the control of the human arm the following hypothesis was proposed (Cruse 1986). To each joint a cost function is attached which defines a cost value for each joint angle.…”

Section: Introductionmentioning

confidence: 99%

“…For this purpose targeting experiments in which the subject was asked to move the arm from a given start point to a given end point (Cruse 1986) are repeated after changing the geometrical configuration of the arm or loading the arm in such a way that different forces have to be developed to perform the movements. Furthermore psychophysical investigations were carried out to find a subjective measure for the comfort of a given joint angle.…”

Section: Introductionmentioning

confidence: 99%

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On the cost functions for the control of the human arm movement

et al. 1990

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Abstract. The aim of our investigation is to understand the mechanisms which control the movement of the human arm. The arm is here considered as a redundant system: the shoulder, elbow and wrist joints, which provide three degrees of freedom, combine to move the hand in a horizontal plane, i.e. a two dimensional space. Thus the system has one extra degree of freedom. Earlier investigations of the static situation led to the hypothesis that independent cost functions were attached to each of the three joints and that the configuration chosen for a given target position is that which provides the minimum total cost (Cruse 1986). The aim of the current investigation was to look for measurable values corresponding to the hypothetical cost functions. Experiments using pointers of different lengths attached to the hand showed that the strategy in choosing the joint angles are independent of the limb length. The muscle force necessary to reach a given angle is increased by a spring mounted across a joint. In this situation the angles of the loaded joint are changed for a given target point to give way to the force effect. This leads to the conclusion that the hypothetical cost functions are not independent of the physiological costs necessary to hold the joint at a given angle. The cost functions seem to depend on joint angle and on the force which is necessary to hold the joint in a given position. Cost functions are measured by psychophysical methods. The results show U-shaped curves which can be approximated by parabolas. The position of minimum cost (maximum comfort) for one joint showed no or weak dependency on the angles of the other joints. For each subject these "psychophysical" cost functions are compared with the hypothetical cost functions. The comparison showed reasonable agreement. This supports the assumption that the psychophysically measured "comfort functions" provide a measure for the hypothetical cost functions postulated to explain the targeting movements. Targeting experiments using a four joint arm which has two extra degrees of freedom showed a much larger scatter compared to the three joint arm. Nevertheless, the results still conform to the hypothesis that also in this case the minimum cost principle is applied to solve the redundancy problem. As the cost function for the whole arm shows a large minimum valley, quite a large range of arm positions is possible of about equal total costs. The scatter does not result from pure randomness but seems to be mainly produced by the fact that the angles at the end of the movement depend on the value of the joint angles at the beginning of the movement.

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Section: Discussionmentioning

confidence: 54%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the cost functions for the control of the human arm movement

et al. 1990

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Motor Control

Heuer

2003

Handbook of Psychology

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Skilled movements require the determination of motor outflow which is appropriate for a certain intended motor pattern; this poses an intricate control problem because of the complex transformations on the way from neural activity to actual limb movements. Solutions are reached by combinations of feedforward and feedback processes. Feedforward processes start before the physical movement and embrace a representation which anticipates it. This anticipatory representation is involved in control and can be modeled in different ways, for example, as a generalized motor program or as a neural network. Sensory information is required both to adapt the anticipatory movement representation to the environment and for feedback‐based corrections, but it is not necessarily the same kind of information on which perceptual awareness is based. Many tasks require the coordinated action of different limbs. While the interactions between the limbs involved are largely tuned to the task requirements, there are constraints which are hard or even impossible to overcome. These constraints originate at different levels of motor control. Overall motor control reveals a remarkable degree of flexibility in adjusting to new visuo‐motor transformations and force fields.

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Robotic Pick‐and‐Place Operations in Multifunctional Liquid Crystal Elastomers

Lyu

Astam

Sánchez‐Somolinos

et al. 2022

Advanced Intelligent Systems

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Pick‐and‐place operations for transporting objects precisely to a target position are a prominent function of (soft‐) robotic systems. Therefore, there is great interest in industry to improve the characteristic gripping, holding, and releasing methods involved in pick‐and‐place operations. Within living organisms such as octopi, nature demonstrates that multiple types of conjointly working actuators are required for flexible pick‐and‐place operations. Herein, a multifunctional soft robotic arm is developed, capable of transporting an object within 3D space. The soft robotic arm consists of two structural actuators (rotating base and lifting unit) and a suction cup‐based gripper. The structural actuator acts as both the load bearing and actuating components of the robotic system. Yet, the gripper is the crucial innovation within the robotic arm. A cephalopod‐limb‐inspired gripper functioning through the reversible flat‐to‐conical deformation of azimuthally aligned liquid crystal elastomer (LCE) films is proposed. The pressure‐generating actuation mechanism of the gripper means that no external device is needed to operate the gripping function. Akin to natural systems, the in‐tandem operation of the actuators in the soft robotic arm allows for multifactored tasks. Yet, the design achieves this through the use of a single material, which is not innate in natural archetypes.

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Constraints for joint angle control of the human arm

Cited by 189 publications

References 5 publications

On the cost functions for the control of the human arm movement

On the cost functions for the control of the human arm movement

Motor Control

Robotic Pick‐and‐Place Operations in Multifunctional Liquid Crystal Elastomers

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