Wrist Orientation Research Articles

Physical Human Interactive Guidance: Identifying Grasping Principles From Human-Planned Grasps

We present a novel and simple experimental method called physical human interactive guidance to study human-planned grasping. Instead of studying how the human uses his/her own biological hand or how a human teleoperates a robot hand in a grasping task, the method involves a human interacting physically with a robot arm and hand, carefully moving and guiding the robot into the grasping pose, while the robot's configuration is recorded. Analysis of the grasps from this simple method has produced two interesting results. First, the grasps produced by this method perform better than grasps generated through a state-of-the-art automated grasp planner. Second, this method when combined with a detailed statistical analysis using a variety of grasp measures (physics-based heuristics considered critical for a good grasp) offered insights into how the human grasping method is similar or different from automated grasping synthesis techniques. Specifically, data from the physical human interactive guidance method showed that the human-planned grasping method provides grasps that are similar to grasps from a state-of-the-art automated grasp planner, but differed in one key aspect. The robot wrists were aligned with the object's principal axes in the human-planned grasps (termed low skewness in this paper), while the automated grasps used arbitrary wrist orientation. Preliminary tests show that grasps with low skewness were significantly more robust than grasps with high skewness (77-93%). We conclude with a detailed discussion of how the physical human interactive guidance method relates to existing methods to extract the human principles for physical interaction.

ACCELEROMETER−BASED CONTROL OF WEARABLE AUDIO RECORDERS

Accelerometer-based orientation and/or movement detection for controlling wearable audio recorders, such as wrist-worn audio recorders, resulting in button-free operation of the audio recorders. Operating a button-free wearable audio recorder does not rely on conventional switches that are often small, difficult to operate, and not very reliable. A wrist-worn audio recorder can use an accelerometer to detect the natural orientation and/or movement of a user's wrist and subsequently activate a corresponding audio-recorder function, for instance recording or playback, without requiring the user to remember to activate the audio-recorder function. In addition, a wearable audio recorder with a vibration mechanism can use this method to remind a user of an undesirable repeated movement, such as restless leg movement. In such applications, and many others, accelerometer-based control of a wearable audio recorder offers significant advantages over conventional means of control, particularly in terms of ease of use and durability.

Grasp Movement Decoding from Premotor and Parietal Cortex

Despite recent advances in harnessing cortical motor-related activity to control computer cursors and robotic devices, the ability to decode and execute different grasping patterns remains a major obstacle. Here we demonstrate a simple Bayesian decoder for real-time classification of grip type and wrist orientation in macaque monkeys that uses higher-order planning signals from anterior intraparietal cortex (AIP) and ventral premotor cortex (area F5). Real-time decoding was based on multiunit signals, which had similar tuning properties to cells in previous single-unit recording studies. Maximum decoding accuracy for two grasp types (power and precision grip) and five wrist orientations was 63% (chance level, 10%). Analysis of decoder performance showed that grip type decoding was highly accurate (90.6%), with most errors occurring during orientation classification. In a subsequent off-line analysis, we found small but significant performance improvements (mean, 6.25 percentage points) when using an optimized spike-sorting method (superparamagnetic clustering). Furthermore, we observed significant differences in the contributions of F5 and AIP for grasp decoding, with F5 being better suited for classification of the grip type and AIP contributing more toward decoding of object orientation. However, optimum decoding performance was maximal when using neural activity simultaneously from both areas. Overall, these results highlight quantitative differences in the functional representation of grasp movements in AIP and F5 and represent a first step toward using these signals for developing functional neural interfaces for hand grasping.

Pointing with the wrist: a postural model for Donders’ law

The central nervous system uses stereotypical combinations of the three wrist/forearm joint angles to point in a given (2D) direction in space. In this paper, we first confirm and analyze this Donders' law for the wrist as well as the distributions of the joint angles. We find that the quadratic surfaces fitting the experimental wrist configurations during pointing tasks are characterized by a subject-specific Koenderink shape index and by a bias due to the prono-supination angle distribution. We then introduce a simple postural model using only four parameters to explain these characteristics in a pointing task. The model specifies the redundancy of the pointing task by determining the one-dimensional task-equivalent manifold (TEM), parameterized via wrist torsion. For every pointing direction, the torsion is obtained by the concurrent minimization of an extrinsic cost, which guarantees minimal angle rotations (similar to Listing's law for eye movements) and of an intrinsic cost, which penalizes wrist configurations away from comfortable postures. This allows simulating the sequence of wrist orientations to point at eight peripheral targets, from a central one, passing through intermediate points. The simulation first shows that in contrast to eye movements, which can be predicted by only considering the extrinsic cost (i.e., Listing's law), both costs are necessary to account for the wrist/forearm experimental data. Second, fitting the synthetic Donders' law from the simulated task with a quadratic surface yields similar fitting errors compared to experimental data.

Efficient and practical determination of grasping configurations for anthropomorphic hands

AbstractThe paper presents a methodology to rapidly solve the inverse kinematics of anthropomorphic hands, which is particularized for a mechanical hand considering 27 degrees of freedom. Given the contact points and normal directions on an object surface, the proposed algorithm finds the joint values and the wrist position and orientation that make the fingertips satisfy the contact constraints. The approach combines an iterative algorithm with an off-line analysis that allows significant reductions of the execution time. The approach has been implemented and the paper includes application examples. The effectiveness and fast execution of the algorithm is demonstrated with statistical results.

The Dorsomedial Pathway Is Not Just for Reaching: Grasping Neurons in the Medial Parieto-Occipital Cortex of the Macaque Monkey

Brain control of prehension is thought to rely on two specific brain circuits: a dorsomedial one (involving the areas of the superior parietal lobule and the dorsal premotor cortex) involved in the transport of the hand toward the object and a dorsolateral one (involving the inferior parietal lobule and the ventral premotor cortex) dealing with the preshaping of the hand according to the features of the object. The present study aimed at testing whether a pivotal component of the dorsomedial pathway (area V6A) is involved also in hand preshaping and grip formation to grasp objects of different shapes. Two macaque monkeys were trained to reach and grasp different objects. For each object, animals used a different grip: whole-hand prehension, finger prehension, hook grip, primitive precision grip, and advanced precision grip. Almost half of 235 neurons recorded from V6A displayed selectivity for a grip or a group of grips. Several experimental controls were used to ensure that neural modulation was attributable to grip only. These findings, in concert with previous studies demonstrating that V6A neurons are modulated by reach direction and wrist orientation, that lesion of V6A evokes reaching and grasping deficits, and that dorsal premotor cortex contains both reaching and grasping neurons, indicate that the dorsomedial parieto-frontal circuit may play a central role in all phases of reach-to-grasp action. Our data suggest new directions for the modeling of prehension movements and testable predictions for new brain imaging and neuropsychological experiments.

Intrinsic Constraints of Neural Origin: Assessment and Application to Rehabilitation Robotics

Ideally, robots used for motor rehabilitation, in particular, during assessment, should minimally perturb the voluntary movements of a subject. In this paper, we show how a state-of-the-art back-drivable robot, i.e., a robot that can be moved by the user with a low perceived mechanical impedance, when used for assessment can still perturb the voluntary movements of a subject. In particular, we show that, despite its low mechanical impedance, a robot may still not comply with the intrinsic kinematic constraints, which are of neural origin and are adopted by the human brain to solve redundancy in motor tasks. Specifically, the redundant task under consideration is the 2-D pointing task, which is performed by a subject with the sole use of the wrist [3 degree of freedom (DOF) kinematics]. Wrist orientations during pointing tasks are assessed in two different scenarios. In the first experiment, a lightweight handheld device is used, which introduces no loading effect. In the second experiment, similar pointing tasks are performed with the subject interacting with a state-of-the-art robot for wrist rehabilitation. In the first case, intrinsic kinematic constraints arise as 2-D surfaces embedded in the 3-D space of wrist configuration. Such surfaces are typically subject-dependent and reveal personal motor strategies. In the second case, a strong influence of the robot is remarked. In particular, 2-D surfaces still arise but are similar for all subjects and are referable to a mechanical origin (excessive loading by the robot). The assessment approach described in this paper, including both the experimental apparatus and data-analysis method, can be used as a test for the degree of back-drivability of mechanisms and robots in relation to constraints of neural origin, thus allowing the design of robots that can actually cope with such constraints. The clinical potential impact is also discussed.

Postural instability does not necessarily correlate to poor performance: case in point

It is very important for surgeons who perform minimally invasive surgery (MIS) to maintain proper postural stability, which kinematic research can determine. Previous studies in surgical ergonomics have shown that postural stability is correlated to instrument type, task difficulty, and skill level. What should also be considered is that surgeons may strategically change stance or joint movement to achieve better surgical outcomes while potentially subjecting themselves to greater risk. Background information about subjects, e.g., joint impairment, should be considered an important surgical ergonomic element. Such information can lead to more realistic and accurate conclusions about postural stability and joint kinematics. A highly experienced and skilled right-handed surgeon developing carpal tunnel syndrome in both wrists was recruited into a small (6 subjects) performance study of pegboard transfer and circle-cutting tasks from the Fundamentals of Laparoscopic Surgery (FLS) skill set. Joint kinematics and postural data were collected using two associated force plates and a motion capture system of 12 digital, high-resolution, high-speed, infrared cameras. Each task was completed in less than 90 s. In pegboard transfer, the subject increased shoulder abduction angle to align his hand and forearm and minimize wrist flexion. When circle-cutting required excessive wrist flexion, the subject maintained his lower body position and stance while twisting his torso, a strategy that appeared to stabilize tangential direction related to cutting while maintaining a fixed orientation of forearm, wrist, and hand. In another circle-cutting trial, the subject changed his stance primarily by shifting foot position as necessary to obtain better scissor approach angles. These compensatory, strategic movements caused an increase in overall postural sway but did not represent postural instability. This case study indicated that poor joint kinematics or postural stability does not necessarily correlate to poor performance. Instead, they may indicate positive compensatory or strategic movements.

Functional properties of grasping-related neurons in the dorsal premotor area F2 of the macaque monkey.

We investigated the properties of neurons located in the distal forelimb field of dorsal premotor area F2 of macaque monkey using a behavioral paradigm for studying the neuronal discharge during observation (object fixation condition) and grasping of different 3-dimensional objects with and without visual guidance of the movement (movement in light and movement in dark conditions, respectively). The main result is that almost all studied neurons were selective for both the type of prehension and the wrist orientation required for grasping an object. Three categories of neurons were found: purely motor, visually modulated, and visuomotor neurons. The discharge of purely motor neurons was not affected by either object presentation or by the visual feedback of the hand approaching to and interacting with the object. Visually modulated neurons presented a different discharge in the 2 movement conditions, this determining a decrease in selectivity for the grip and wrist orientation in the movement in dark condition. Visuomotor neurons typically discharged during the object fixation task even in the absence of any grasping movement. Nine of them also displayed a different discharge rate between the 2 movement conditions. Congruence was observed between the neuron response during the most effective type of prehension and the neuron response during observation of the object requiring that particular prehension. These results indicate an important role of F2 in the control of goal-related hand movements.

Effects of lesions to area V6A in monkeys.

In order to assess the role played by area V6A in visuomotor control, two adult green monkeys ( Cercopithecus aethiops) were subjected to small, bilateral lesions in the anterior bank of the parieto-occipital sulcus. Before and after the lesions, monkeys were tested for naturally designed reaching, grasping and picking-up pieces of food from various positions on a plate and from a differently oriented narrow slit. All movements were recorded with closed circuit TV and analysed offline on a single-photogram basis for defective reaching and wrist orientation. V6A lesions provoked parietal weakness, reluctance to move, and specific deficits in reaching, wrist orientation and grasping. Recovery from the observed deficits was rapid, even after a second, contralateral lesion was given, creating a bilateral lesion. Thus, together with previous anatomical and electrophysiological data, these results directly support the hypothesis that area V6A is part of the network involved in the control of reaching movements and wrist orientation.

A solution to the velocity control of redundant robots

Abstract Flexible and dexterous manipulation of modern industrial applications requires the use of robots with extra (more than six) axes of motion (degrees of freedom). Thus the kinematic and control considerations of redundant robots are currently of increasing interest to both theorists and practitioners. For this type of robots, a closed-form solution of the inverse kinematic problem is not possible, and the classical approach is to use the pseudoinverse of the Jacobian matrix together with an extra criterion function. This paper presents an iterative technique for velocity control, which is suitable for redundant robots with a maximum of 11 d.o.f. This technique, which splits the Jacobian inversion problem into two subproblems (wrist position and wrist orientation), provides an exact solution for the arm tip position and an approximate solution for the wrist orientation. The convergence of the procedure is examined and a simulated example is included.

Peak volitional torques for wrenches and screwdrivers

Effects of grip shape (regular, circular, square, and triangular), wrist orientation (3 for screwdrivers and 7 for wrenches) and duration of repeated exertions on the maximum torque males and females could exert in different postures with 4 wrenches and 4 screwdrivers were investigated experimentally. Quantitative data were collected by conducting two independent sequential experiments. Circular grips for wrenches and triangular grips for screwdrivers maximized torque exertion capability. The peak torque declined with the duration of repeated exertions but stabilized after 180 s. Wrist orientation also had a significant influence on how much torque individuals could exert. A third experiment generated torque data for two additional body postures that were not included in previous works. From this investigation, correction factors were developed to generate peak torque exertion capability data of individuals with wrenches and screwdrivers for a variety of conditions dictated by body posture, wrist orientation, duration of repeated exertions, and grip shape. The paper includes the basic torque exertion capability design data tables and the correction factors.

Robot performance measurements using automatic laser tracking techniques

This paper describes two laser tracking techniques currently under development at the National Bureau of Standards for robot performance measurements. Tests indicate that the system can be used in real-time to determine the three-dimensional static and dynamic positioning accuracy of a robot end-effector to a few parts in 100,000 (i.e. 12.5–50 μm for a medium to large size robot), and wrist orientations to within 2 sec of arc. Both systems would be simple and compact enough to be considered as a general-purpose portable calibrating tool for robots (or CNC machines), or as an integral part of a robotic system providing real-time position feedback of the end-effector independent of the position and angle feedback of joint members. The ability to dynamically and statistically measure the position of an end-effector to the above accuracy has significant ramifications with regard to meaningful robot performance measurements, and the potential of these systems in other industrial and engineering applications.

Iterative coordinate transformation procedure for one class of robots

A necessary feature of robot systems is a capability to process robot paths in terms of Cartesian coordinates. However, the so-called articulated robot arms which represent the more advanced systems operate in terms of their revolute and sliding joint coordinates, and these do not lend themselves easily to translation into Cartesian equivalents. As a rule, the direct (joint-to-Cartesian space) coordinate transformation can be solved for in closed form. As for the inverse (Cartesian-to-joint) transformation, for some rather common arm designs practical solutions cannot be found in closed form. An iterative procedure for one such class of articulated robots is presented. The procedure produces an exact solution for the wrist tip position coordinates and an approximate solution for the wrist orientation coordinates. The convergence characteristics of the procedure are discussed.

An investigation of the relationship between displacements of the finger and wrist joints and the extrinsic finger flexor tendons

Several investigators have developed biomechanical models of finger flexor tendon displacements during pinching or gripping exertions of hands. Landsmeer has developed the most comprehensive set of models for this purpose. This paper describes experiments in which various sized cadaver hands were used to statistically evaluate the Landsmeer models. In so doing, the effects of hand and wrist anthropometry are included. The results indicate that the tendons displace in relation to joint positions as described by that Landsmeer model in which the tendon is depicted as sliding over the curved articular surface of the proximal bone of the joint. Joint thickness effects were found to modify the parameters in the model as intuitively expected. An empirical prediction model of the anthropometric effects was developed. Further, the tendon displacements for various wrist orientations were expressed empirically for the first time and were shown to be consistent with expected anatomical considerations.

The influence of forearm and wrist orientation on static grip strength as a design criterion for hand tools : Terrell, R., and Purswell, J.L. In: Proceedings of 6th Congress of the International Ergonomics Association “Old World, New World, One World” and Technical Programme of the 20th Annual Meeting of the Human Factors Society, Jul 1976, pp 28–32

The influence of forearm and wrist orientation on static grip strength as a design criterion for hand tools : Terrell, R., and Purswell, J.L. In: Proceedings of 6th Congress of the International Ergonomics Association “Old World, New World, One World” and Technical Programme of the 20th Annual Meeting of the Human Factors Society, Jul 1976, pp 28–32

The Influence of Forearm and Wrist Orientation on Static Grip Strength as a Design Criterion for Hand Tools

The amount of force required to use a hand tool and its relationship to the user's capacity to exert this force is a critical design criterion of hand tools, often affecting the immediate safety of the tool user and the propensity of the tool to cause injury to the user with long-term use. Because the wrist is often placed in deviated positions, the available data on grip strength with an undeviated wrist configuration may not be applicable to the design of many hand tools. This study demonstrates the decreases in grip strength due to wrist deviations and forearm rotation. The position of maximal static grip strength is the neutral wrist with a supinated forearm. Decrements from the neutral position for wrist flexion, hyperextension, radial flexion and ulnar flexion are 30%, 22%, 18% and 15%, respectively. The pronated forearm allows only 87% of the strength of the supinated forearm, and the differences between the supinated and the midposition forearm are not significant.