Arm Compliance Research Articles

Topology, dynamics, and control of a muscle-architected soft arm

Muscular hydrostats, such as octopus arms or elephant trunks, lack bones entirely, endowing them with exceptional dexterity and reconfigurability. Key to their unmatched ability to control nearly infinite degrees of freedom is the architecture into which muscle fibers are weaved. Their arrangement is, effectively, the instantiation of a sophisticated mechanical program that mediates, and likely facilitates, the control and realization of complex, dynamic morphological reconfigurations. Here, by combining medical imaging, biomechanical data, live behavioral experiments, and numerical simulations, an octopus-inspired arm made of [Formula: see text]200 continuous muscle groups is synthesized, exposing "mechanically intelligent" design and control principles broadly pertinent to dynamics and robotics. Such principles are mathematically understood in terms of storage, transport, and conversion of topological quantities, effected into complex 3D motions via simple muscle activation templates. These are in turn composed into higher-level control strategies that, compounded by the arm's compliance, are demonstrated across challenging manipulation tasks, revealing surprising simplicity and robustness.

Compliance control of a rehabilitation massage robot in dynamic scenes

Abstract Medical robots encounter challenges when interacting with people or operating in complex and dynamic environments due to the variability of human morphology and the unpredictability of environmental changes. Compliance of human-robot interaction is the primary goal of medical robots when in contact with the human body. Therefore, robots must be able to adaptively adjust their forces and actions to ensure safety and comfort during the contact process. This paper focuses on the compliance control of rehabilitation massage robots in dynamic scenes. We propose a mechanical arm compliance control method based on the Soft Actor-Critic (SAC) algorithm. We construct a simulated massage environment in a dynamic scene according to the task requirements and design a massage path covering the entire back. Under the framework of deep reinforcement learning, the optimal reward function is designed to achieve constant force control under dynamic scenes. Through numerous simulation experiments, we have verified that the robotic arm can move along the predetermined path under the massage while maintaining a constant contact force with the body simulation module. The actual contact force and target contact force control are realized within 0.1 N.

AquaClimber: a limbed swimming and climbing robot based on reduced order models

Many legged robots have taken insight from animals to run, jump, and climb. Very few, however, have extended the flexibility of limbs to the task of swimming. In this paper, we address the study of multi-modal limbed locomotion by extending our lateral plane reduced order dynamic model of climbing to swimming. Following this, we develop a robot, AquaClimber, which utilizes the model’s locomotive style, similar to human freestyle swimming, to propel itself through fluid and to climb vertical walls, as well as transition between the two. A comparison of simulation and model results indicate that the simulation can predict how hand design, arm compliance, and driving frequency affect swimming speed and behavior. Using this reduced order model, we have successfully developed the first limbed aquatic-scansorial multi-modal robot.

Analysis of the Compliance Properties of an Industrial Robot with the Mozzi Axis Approach

In robotic processes, the compliance of the robot arm plays a very important role. In some conditions, for example, in robotic assembly, robot arm compliance can compensate for small position and orientation errors of the end-effector. In other processes, like machining, robot compliance may generate chatter vibrations with an impairment in the quality of the machined surface. In industrial robots, the compliance of the end-effector is chiefly due to joint compliances. In this paper, joint compliances of a serial six-joint industrial robot are identified with a novel modal method making use of specific modes of vibration dominated by the compliance of only one joint. Then, in order to represent the effect of the identified compliances on robot performance in an intuitive and geometric way, a novel kinematic method based on the concept of “Mozzi axis” of the end-effector is presented and discussed.

Hypertrophic cardiomyopathy disease results from disparate impairments of cardiac myosin function and auto-inhibition

Hypertrophic cardiomyopathies (HCM) result from distinct single-point mutations in sarcomeric proteins that lead to muscle hypercontractility. While different models account for a pathological increase in the power output, clear understanding of the molecular basis of dysfunction in HCM is the mandatory next step to improve current treatments. Here, we present an optimized quasi-atomic model of the sequestered state of cardiac myosin coupled to X-ray crystallography and in silico analysis of the mechanical compliance of the lever arm, allowing the systematic study of a large set of HCM mutations and the definition of different mutation classes based on their effects on lever arm compliance, sequestered state stability, and motor functions. The present work reconciles previous models and explains how distinct HCM mutations can have disparate effects on the motor mechano-chemical parameters and yet lead to the same disease. The framework presented here can guide future investigations aiming at finding HCM treatments.

An Interventional Quality Improvement Study to Assess the Compliance to Cardiopulmonary Resuscitation Documentation in an Indian Teaching Hospital.

Background:Cardiopulmonary resuscitation (CPR) should be performed as per the international guidelines; however, compliance to these guidelines is difficult to assess. This study was conducted to determine the compliance to American Heart Association (2010) guideline on CPR documentation by among resident physicians before and after resident training (two arms).Methods:This pre–postinterventional quality improvement study was conducted in a referral center, North India. Data of hospitalized in-hospital CPR patients were collected in the form of quality indicators (checklists) as defined by the guideline and compared between two arms of before–after resident training. Residents were given appropriate training in CPR technique as per the guideline. The compliance of CPR documentation was assessed pre- and post-intervention.Results:The baseline arm compliance of various components of CPR documentation was low. The postintervention arm compliances of all components significantly increased (baseline, 2.5% to postintervention, 15.11%, P = 0.03). Individual components assessed were documentation of assessment of responsiveness (65% to 77.9%, P = 0.19), assessment of breathing (37.5% to 58.1%, P = 0.03), assessment of carotid pulse (62.5% to 79%, P = 0.05), rate of chest compressions (20% to 39.5%, P = 0.04), airway management (62.5% to 82.5%, P = 0.02), and compressions to breaths ratio (12.5% to 31.4%, P = 0.02). Documentation of chest compression rate compared to nondocumentation (12 of 42 vs. 11 of 84, P = 0.04) was independently associated with a higher rate of return of spontaneous circulation. The study however did not show any survival benefits.Conclusions:This study establishes that the compliance to CPR documentation is poor as assessed by CPR documentation content and quality, which improves after physician training, but not up to the mark level (100%) that may be due to busy Indian hospital settings and human behavioral factors. Due to ethical constraints of live CPR assessment, this document checklist approach may be considered as an internal quality assessment method for CPR compliance. Furthermore, correct instruction in CPR technique along with proper documentation of the procedure is required, followed up with periodic re-education during the residency period and beyond.

Octopus-inspired multi-arm robotic swimming

The outstanding locomotor and manipulation characteristics of the octopus have recently inspired the development, by our group, of multi-functional robotic swimmers, featuring both manipulation and locomotion capabilities, which could be of significant engineering interest in underwater applications. During its little-studied arm-swimming behavior, as opposed to the better known jetting via the siphon, the animal appears to generate considerable propulsive thrust and rapid acceleration, predominantly employing movements of its arms. In this work, we capture the fundamental characteristics of the corresponding complex pattern of arm motion by a sculling profile, involving a fast power stroke and a slow recovery stroke. We investigate the propulsive capabilities of a multi-arm robotic system under various swimming gaits, namely patterns of arm coordination, which achieve the generation of forward, as well as backward, propulsion and turning. A lumped-element model of the robotic swimmer, which considers arm compliance and the interaction with the aquatic environment, was used to study the characteristics of these gaits, the effect of various kinematic parameters on propulsion, and the generation of complex trajectories. This investigation focuses on relatively high-stiffness arms. Experiments employing a compliant-body robotic prototype swimmer with eight compliant arms, all made of polyurethane, inside a water tank, successfully demonstrated this novel mode of underwater propulsion. Speeds of up to 0.26 body lengths per second (approximately 100 mm s−1), and propulsive forces of up to 3.5 N were achieved, with a non-dimensional cost of transport of 1.42 with all eight arms and of 0.9 with only two active arms. The experiments confirmed the computational results and verified the multi-arm maneuverability and simultaneous object grasping capability of such systems.

Calibration of Kinematic Parameters of Robot Arm Using Laser Tracking System: Compensation for Non-Geometric Errors by Neural Networks and Selection of Optimal Measuring Points by Genetic Algorithm

Offline teaching based on high positioning accuracy of a robot arm is desired to take the place of manual teaching. In offline teaching, joint angles are calculated using a kinematic model of the robot arm. However, a nominal kinematic model does not consider the errors arising in manufacturing or assembly, not to mention the non-geometric errors arising in gear transmission, arm compliance, etc. Therefore, a method of precisely calibrating the parameters in a kinematic model is required. For this purpose, it is necessary to measure the three-dimensional (3-D) absolute position of the tip of a robot arm. In this paper, a laser tracking system is employed as the measurement apparatus. The geometric parameters in the robot kinematic model are calibrated by minimizing errors between the measured positions and the predicted ones based on the model. The residual errors caused by non-geometric parameters are further reduced by using neural networks, realizing high positioning accuracy of sub-millimeter order. To speed up the calibration process, a smaller number of measuring points is preferable. Optimal measuring points, which realize high positioning accuracy while remaining small in number, are selected using Genetic Algorithm (GA).

Effects of walking with blood flow restriction on limb venous compliance in elderly subjects

Venous compliance declines with age and improves with chronic endurance exercise. KAATSU, an exercise combined with blood flow restriction (BFR), is a unique training method for promoting muscle hypertrophy and strength gains by using low-intensity resistance exercises or walking. This method also induces pooling of venous blood in the legs. Therefore, we hypothesized that slow walking with BFR may affect limb venous compliance and examined the influence of 6 weeks of walking with BFR on venous compliance in older women. Sixteen women aged 59-78 years were partially randomized into either a slow walking with BFR group (n = 9, BFR walk group) or a non-exercising control group (n = 7, control group). The BFR walk group performed 20-min treadmill slow walking (67 m min(-1) ), 5 days per week for 6 weeks. Before (pre) and after (post) those 6 weeks, venous properties were assessed using strain gauge venous occlusion plethysmography. After 6 weeks, leg venous compliance increased significantly in the BFR walk group (pre: 0·0518 ± 0·0084, post: 0·0619 ± 0·0150 ml 100 ml(-1) mmHg(-1) , P<0·05), and maximal venous outflow (MVO) at 80 mmHg also increased significantly after the BFR walk group trained for 6 weeks (pre: 55·3 ± 15·6, post: 67·1 ± 18·9 ml 100 ml(-1) min(-1) , P<0·01), but no significant differences were observed in venous compliance and MVO in the control group. In addition, there was no significant change in arm compliance in the BFR walk group. In conclusion, this study provides the first evidence that 6 weeks of walking exercise with BFR may improve limb venous compliance in untrained elder female subjects.

2A1-A10 レーザートラッキングシステムを用いたロボットの機構キャリブレーション : ギア伝達誤差とアームコンプライアンスのNNによる補正とGAによる最適計測点の選択

2A1-A10 レーザートラッキングシステムを用いたロボットの機構キャリブレーション : ギア伝達誤差とアームコンプライアンスのNNによる補正とGAによる最適計測点の選択

Effects Of 6-week Kaatsu Walking Training On Limb Venous Compliance In Elderly Subjects

Venous compliance declines with age and improves with chronic endurance exercise. KAATSU-walking is a unique training method for promoting muscle hypertrophy and strength gains under the conditions with restricted venous blood flow, and inducing venous pooling of blood, which may affect limb venous compliance. However, the effects of KAATSU training on venous properties have not been investigated. PURPOSE: This study investigated the influence of a 6-week-walk training combined with KAATSU on venous properties in older men and women. METHODS: Twenty-two elderly men and women, aged 60-78 years, were randomized into either a KAATSU-walk training group (n=11, KAATSU-walk) or a non-exercising control group (n=11, Control). The KAATSU-walk group performed 20 min treadmill walking (67 m/min), five days/wk for 6 wk. A non-exercising group was advised to perform daily slow walk for 20 min five days/wk during the study. Before (pre) and after (post) 6 wk, strain gauge venous occlusion pletysmography was used to assess limb venous vascular properties. Venous volume variation (VVV) was defined as the maximal relative volume increase in the limb at a certain cuff pressure, and VVV at different occlusion pressures represents the pressure-volume curve. Compliance was derived from the slope of the pressure-volume curve. Venous emptying rate was calculated as the slope of the tangent at the curve 0.5 s after cuff release. The time 0.5 s after cuff deflation was chosen to avoid any cuff artifact, and the effective pressure of the cuff on the venous system at 0.5 s was calculated by using the pressure-volume curve. RESULTS: Leg venous compliance was significantly increased in KAATSU-walk group (pre 0.066±0.004 ml·100ml-1·mmHg-1, post 0.078±0.007, P<0.05), compared with control group (pre 0.069±0.008; post 0.068±0.04). Leg venous flow resistance decreased (pre 1.31±0.1 mmHg·ml-1·100 ml·min; post 1.08±0.08) in KAATSU-walk group, compared with control group (pre 1.23±0.12; post 1.38±0.07). In contrast, arm compliance did not change significantly in KAATSU-walk and control group. CONCLUSIONS: The present study provides the first evidence that daily KAATSU-walk may be a unique and novel training for improving limb venous compliance in untrained older subjects.

G1501-3-3 三次元マジックハンドの研究 : 第8報,手先負荷に対する静力学的検討(作業ロボット・その他)

This paper is a research on the improvement of a three-dimensional magic-hand (super-multi joint manipulator),which is able to extend and bend spatially. That is, to make use of wire length of three wire-encoders built into the manipulator to reduce the bend of it was examined for estimation of the load and moment toward the hand. The relation of the arm compliance and force was led, and simulated for the relation of the length of the wire to displacement of unit. Moreover, it was clarified to be able to estimate force and direction of the load according to the amount of extension of wires.

Closed-loop multivariable system identification for the characterization of the dynamic arm compliance using continuous force disturbances: a model study

This study presents a new multivariable closed-loop identification technique for estimating the dynamic compliance of the multijoint human arm during posture maintenance. The method is designed for the application of continuous force disturbances that facilitate interaction of the limb with the environment. The dynamic compliance of the arm arises from different physiological mechanisms and is important for maintaining stable postures and to suppress disturbances. Estimates can be useful to analyze the ability of the nervous system to adapt the arm compliance to different types of disturbances and environments. The technique is linear and requires no a priori knowledge of the system. Linear system behavior is justified for posture tasks where the hand position deviates slightly from a reference position. Interaction results in a closed-loop configuration of arm and environment. The problem with previous methods is the restriction to open-loop systems. With the current technique, the dynamic arm compliance is separately estimated from the closed-loop. The accuracy of the identification technique is tested by simulations for different values of the dynamic compliance of the arm and environment and for different methodological parameters. It is concluded that the identification technique is accurate, even for short observation periods and severe noise.

Mechanical Analysis of high precision manipulator

It is of great importance that high precision manipulators are well designed from a mechanical point of view. A thorough analysis of all mechanical aspects concerning an accurate manipulator will make a good basis for further design. This paper presents a new approach to mechanical analysis of high-precision manipulators. A typical six axis anthropomorphic manipulator configuration is chosen as a model for the analysis. The paper is divided into two main parts ; static deformation analysis and dynamic analysis. The static deformation analysis consists of three sub-parts ; link deformation, joint deformation and total mechanical deformation. A simple fixed beam deformation model is used to simulate every link. Both specific gravity and a load attached at the end of the beam is considered. By varying material, outer dimensions and wall thickness it is possible to determine optimal values. Looking at the whole structure with an attacking force at the end, it is possible to select appropriate motor/transmission combinations. Each combination represents compliance and combined with the arm compliance the total deformation can be found. The result shows that deformation due to compliance in the joints represents 97% of the total. Based on the result of the previous section, the dynamic model can be simplified significantly. The arm elements are supposed to be rigid and all the compliances are due to the joint deformation. This gives a coupled mass/spring system to be analysed. The resonance frequencies of the system are found through theoretical analysis and through simulation in a Finite Element based program for Dynamic analysis of Elastic Mechanisms (FEDEM) (Sintef Production Engineering 1993).

A direct compliance control for a parallel link arm. (2nd Report, The stability analysis for the arm with negative stiffness joints).

In the Direct compliance Control (DCC) of robotic arms, the arm compliance which can be selected is limited when only the positive joint stiffness is allowed. This is drawback of the DCC, as the previous paper suggested. One way of removing this is to expand the adjusting ranges of the joint stiffness to negative values. However, this may cause unstable motion of the arm. This paper discusses the stability of the parallel link arm which includes joints with negative stiffness. Through potential energy analysis, the stability condition for the arm is derived, and it is suggested that a parallel link arm structure provides a great benefit in obtaining get stable control motions by robotic arms with negative stiffness joints. A planar parallel link arm with three variable stiffness joints was designed. Using the arm, two compliant motion tasks were carried out and the analytical results were confirmed.