Minimum Number Of Actuators Research Articles

Design and Synthesis of Eight-Legged Spider Robot

Abstract: Less than half the world’s landmass is accessible to existing wheeled and tracked vehicles. But people and animals using their legs can go almost anywhere. Our aim is to develop a new type of rough-terrain robots that capture the mobility, autonomy and speed of living creatures. Such robots will travel in outdoor terrain that is too steep, rutted, rocky, wet, muddy, and snowy for conventional wheeled vehicles. They will travel in cities as well as in our homes, doing chores and providing care, where steps, stairways and household clutter limit the utility of wheeled vehicles. Robots meeting these goals will have various sensors, sophisticated computing and power systems, advanced actuators and dynamic controls. It is marvellous that creatures can go over a rough terrain at speeds which are remarkably higher than practically possible with wheeled vehicles. Indeed, even an individual, by getting down on each of the eight legs if necessary, can travel or climb over terrain which is unreachable for a wheeled or followed vehicle. It is therefore of immense eagerness to realize what machines for land locomotion can do if they are intended to imitate nature. Legged robots can be used for space missions on extraterrestrial planets and in risky places, for example, within an atomic reactor, giving independent legged robots a great potential. less power consumption and weight are further advantages of walking robots, so it is important to use the minimum number of actuators. In this context, the objective of this project is to learn and design a prototype of the Theo-Jansen eight leg strolling robot. The goal is to develop a new mechanical automated walker utilizing eight bar link mechanism. The essential Theo Jansen device is a 13 bar framework that strolls when a crank is rotated. So, utilizing linkages we attempted to imitate nature and put together certain strolling robot which will suite off-road.

Redundancy and overactuation in cephalopod-inspired soft robot arms.

Current soft robotic arms commonly follow traditional - i.e., hard - robot design conventions. Omnidirectional soft arms most commonly consist of segments that contain three parallel longitudinal actuators, or actuator groups, of which one or two are activated to induce bending. This design uses the minimum number of actuators required for omnidirectional bending, which is consistent with traditional robot design but unnecessarily constrains the soft arm design space. The cephalopods that frequently inspire soft robot arms have tens of bundles of longitudinal muscle fibers, and these bundles are distributed around the limb circumference rather than grouped. This article analyzes fluid-driven soft arm architectures with up to 12 actuators, which mimic the redundant and distributed nature of cephalopod arms and tentacles. Over-constraints (activating more than two actuators) were considered, which are possible because soft robots - unlike traditional robots - can tolerate conflicting constraints without jamming. A previously-developed generalizable model was used to simulate design performance, and a subset of the examined architectures were constructed and tested. Many-actuator soft arms achieved high strokes under equivalent load without sacrificing no-load reach and were able to execute near constant-curvature turns with a simple actuation pattern. The framework introduced here also enables cross section variations that are not possible with minimalist designs.

Reducing Anthropomorphic Hand Degrees of Actuation with Grasp-Function-Dependent and Joint-Element-Sparse Hand Synergies

In this paper, a set of grasp-function-dependent and joint-element-sparse hand synergies was proposed. First, hand synergies were extracted from five basic categories of movements by principal component analysis (PCA). Then, varimax rotation was applied on these synergies, so each sparse synergy only represented a limited number of joints. Next, according to the contribution to these sparse synergies, finger joints were clustered into different joint modules. Finally, integrating the joint modules in different categories of hand movements, the minimum number of actuators and joint synergic modules for anthropomorphic hands were determined. The results showed that using 5 groups of joint modules and 7–9 actuators we can achieve the best performance of grasp function and motion flexibility. Furthermore, through the reasonable design of adaptive and hyperextension functional joint modules, anthropomorphic hands can better meet the requirements of different tasks like power grasping and precision pinching. Comparing with traditional finger-based actuation strategy, the joint coupling scheme achieved better anthropomorphic performance and larger workspace. These above findings will benefit the development of mechanical structure design and control method of anthropomorphic hands.

Mechatronics Design and Kinematic Analysis of SMA Spring Actuated Parallel Manipulator

Flexible parallel manipulators can be used as an orienting device because of their precise positioning ability and better stiffness. The flexibility to the manipulator induces challenges in the selection of actuator, sensors and control. The paper presents a novel mechatronics design of a flexible symmetric parallel manipulator with minimum number of actuators used as an orienting device. Shape memory alloy springs (SMA) are used as an actuator because of ease of integration and higher deflection. In order to avoid any contact type sensor which could affect the compliance of the manipulator, the position of SMA spring is calculated indirectly from the kinematic model with the end effector orientation data measured from IMU sensor. The complete experimental set up design including electrical and control circuitry is explained in detail in the work. Preliminary open loop test is conducted on the prototype to understand the SMA response to various current input and to verify the effectiveness of the kinematic model in the actuator length measurement. Closed loop control based on ON/OFF control is implemented in the controller and is tested for step input.

Integrated design optimization of actuator layout and structural ply parameters for the dynamic shape control of piezoelectric laminated curved shell structures

Compared with static shape control, dynamic shape control is more difficult due to its time-varying nature. To improve the control precision and reduce the number of actuators needed, an integrated design optimization model of structure and control is proposed. The following three sets of design variables are considered to minimize the time domain variance between the controlled and desired dynamic shapes: the time-varying actuator voltages, the actuator layout and the structural ply parameters. To satisfy the engineering performance requirements to the greatest extent possible, constraints on the structural mass, the energy, the maximum transient voltage and the number of actuators are considered. Because the control voltages are varying in time, a two-level optimization strategy is adopted. In the inner optimization problem, the Newmark integral method is applied to derive discrete time domain expressions for the shape control equations, and then, the Kuhn-Tucker condition is introduced to calculate the optimal time-varying voltage distribution. To solve the outer optimization problem, because of the coexistence of discrete variables and continuous variables, a simulated annealing algorithm is used. To address the shape control of complicated curved shells, a finite element formulation for an eight-node laminated curved shell element with piezoelectric actuators is derived. Numerical examples show that the proposed integrated design optimization method can significantly improve the control effect and that the optimization of the structural ply parameters plays an important role. Moreover, the control system can be simplified by taking the minimum number of actuators as the objective function when the control accuracy allows.

Optimum design of the reconfiguration system for a 6-degree-of-freedom parallel manipulator via motion/force transmission analysis

This research introduces a 6-degree-of-freedom parallel manipulator with a reconfigurable fixed base; the manipulator performance has been evaluated to select the most suitable reconfiguration system. The optimal design of the parallel manipulator refers to the enhancement of robot behavior achieved by the geometrical variation of the fixed platform. Motion/force transmission, with the aid of the principle of power conservation, defines the manipulator capacity to transmit its force from the actuated joints to the end-effector from different reconfiguration approaches and vice versa considering the stiffness analysis. Results allow inferring that reconfiguration of the fixed base enhances the performance of this parallel manipulator. The proposal of the reconfiguration system allows obtaining a reconfigurable parallel robot with the minimum number of actuators.

Vibration Regulation of Kinematically Constrained Cable-Driven Parallel Robots With Minimum Number of Actuators

Cable-driven parallel robots (CDPRs) provide fast motions over considerably large workspaces, however, they suffer from undesired vibrations. Kinematically constrained CDPRs (KC-CDPRs) are CDPRs that are designed intentionally to have certain kinematic constraints, which help minimizing undesired modes of motion, enhancing stiffness, and hence establishing robustness to external disturbances. This article focuses on the vibration regulation of KC-CDPRs using minimal number of actuators. Considering a generic vibration model with six mode shapes, the effects of configuration of a set of four attachable actuators on energy dissipation of a KC-CDPR system are investigated. Accordingly, a measure is developed to quantify each configuration's capacity of vibration suppression in all six degrees of freedom (DoFs) all over the KC-CDPR workspace. In order to demonstrate the use of the proposed measure, five different actuator configurations are analyzed in detail. Moreover, an optimal proportional–derivative (PD) controller is designed to minimize the maximum settling time of the vibration signals. The proposed actuator configuration effectiveness measure, the provided comparative analysis of configurations, and the proposed optimal PD controller are evaluated and verified to be effective via an experimental KC-CDPR setup, for a planar warehousing case study of vibration regulation in all six DoFs using only four actuators. Comparison of the experimental results of the proposed controller with ${H}_{\infty }$ -based vibration controllers of CDPR demonstrates the superior characteristics of the proposed control technique.

Co-Ex: A Torque-Controllable Lower Body Exoskeleton for Dependable Human-Robot Co-existence.

In this paper, we present our research study concerning the design and development of an exoskeleton that aims to provide 3D walking support with minimum number of actuators. Following a prior simulation study, the joint configuration was primarily determined. In order for the exoskeleton to possess advanced characteristics, the following design criteria were investigated: i) all the actuators (hip/knee/ankle) were deployed around the waist area to decrease leg weight and improve wearability, ii) custom-built series elastic actuators were used to power system for high fidelity torque-controllability, iii) 3D walking support is potentially enabled with reduced power requirements. As a result, we built the first actual prototype to experimentally verify the aforementioned design specifications. Furthermore, the preliminary torque control experiments indicated the viability of torque control.

Actuation distribution and workspace analysis of a novel 3(3RRlS) metamorphic serial-parallel manipulator for grasping space non-cooperative targets

Capturing non-cooperative targets in space is a cutting-edge technology in the aerospace field. In this study, a novel n(3RRlS) metamorphic serial-parallel manipulator (MSPM) with multiple working conditions is proposed, which can serve as the fingers of a large-scale reconfigurable space multifingered hand (LSRSMFH). First, a limb combination coding method is proposed to describe the topological graph and determine the isomorphism of the n(3RRlS) MSPM. Subsequently, the topological graphs and the limb combination codes (LCCs) of the 1(3RRlS) MSPM, 2(3RRlS) MSPM and 3(3RRlS) MSPM are further analyzed, and the isomorphism of all the actuation distribution configurations (ADCs) and metamorphic configuration states (MCSs) is determined. Second, a two-actuator method is applied for the n(3RRlS) MSPM, and the workspaces of all MCSs of all ADCs of the 1(3RRlS) MSPM, 2(3RRlS) MSPM and 3(3RRlS) MSPM are analyzed using a transformation method. The results show that the n(3RRlS) MSPM can realize their respective functions of the LSRSMFH under three working conditions with the minimum number of actuators, which can reduce the number of actuators and the weight of the LSRSMFH and can gain benefits in multitask adaptability, simplified control, precision and rigidity improvement, energy saving and risk reduction.

A Novel Monolithic Soft Robotic Thumb for an Anthropomorphic Prosthetic Hand

The thumb of a natural hand or a prosthetic hand plays a significant role in realizing a hand's grasping and manipulation activities. This requires that mechanical design of a prosthetic hand should allow its thumb to perform both abduction/adduction and flexion/extension in order to mimic a natural hand's grasping and manipulation abilities with a minimum number of actuators. In this letter, we propose a novel monolithic soft robotic thumb for an anthropomorphic and transradial prosthetic hand. The thumb and the whole prosthetic hand were fabricated using a low-cost three-dimensional printing technology, with sizes comparable to those of real human ones but with much lighter weights. Based on the concepts of soft robotics and underactuation, the thumb shows significant mechanical compliance and performs well in power grasps, precision grasps, and lateral grasps of different shaped and sized household objects. The soft thumb has two modes of operation based on an innovative and compact mechanism, and one actuator only offers grasping versatility (capable of both abduction/adduction and flexion/extension). This novel thumb minimizes the number of actuators and reduces the corresponding requirement on space consumption (for housing its actuators) and power consumption, which are favorable features to develop low-cost, low-power and low-weight prosthetic hands with intrinsic compliance.

Optimal structural synthesis of agricultural legged robot with minimal damage on soil

Optimal structural synthesis of agricultural legged robot is carried out, that causes minimal damage on soil and provide the most favorable conditions for plant growth. A rational structure of a legged robot with orthogonal propel based on kinematic decoupling of the motion is proposed. Most of traditionally used walking robots have universal “insect type” structure with multiple actuators to be synchronized which result in complex control. The alternative design is realizing a concept of functional independence of the actuators when each actuator is responsible for specified purpose: the main actuators are responsible for rectilinear translational motion of cabine/chassis whereas another group of actuators are responsible for adaptation purposes and anothers participate in turning/maneuvering. This allows to carry out the cabine/hull shifting and turning with a minimum number of actuators and simplified control. A new kinematic equivalent scheme of turning mechanism was proposed in order to optimize turning modes of the robot. The proposed planar model allows to determine the optimal parameters of the robot by applying multicriteria synthesis methods of parallel robot manipulators based on isotropy, maneuverability and other criteria.

Design of a Humanoid Shoulder Complex Emulating Human Shoulder Girdle Motion Using the Minimum Number of Actuators

This paper describes a design for a humanoid shoulder complex that replicates human shoulder girdle motion. The goal here is to use the minimum number of actuators to keep the mechanism as light as possible to help ensure that a humanoid is not too top heavy. The human shoulder girdle has two degrees-of-freedom (DOF), which means the minimum number of actuators is also two. The proposed mechanism is a novel parallel platform with two DOF that acts as a pointing mechanism. As the mechanism is articulated the end-effector moves, which results in contraction or elongation, mimicking the natural motion of the human shoulder girdle. A parallel platform was chosen because of the inherent rigidity and a large workspace is not necessary. The mechanism presented here was chosen because of its simplicity and ability to track human shoulder girdle motion. Motion studies were conducted to collect data representing human shoulder girdle motion, which was used to optimize the mechanism for tracking human shoulder girdle motion as closely as possible. A second optimization was performed to ensure that the mechanism avoids singularities throughout its entire range of motion. The results show that this design closely replicates human shoulder girdle motion and is well-suited for use as a humanoid shoulder girdle to increase the range of motion for a humanoid arm.

Simultaneous Displacement and Internal Force Prescription in Shape Control of Pin-Jointed Assemblies

This paper presents a direct method for controlling nodal displacements, internal bar forces, and simultaneously both nodal displacements and internal bar forces, of a prestressable pin-jointed assembly under load. The method is aimed at static shape control of geometrically sensitive structures through length actuations in selected bars. The paper discusses identification of the most effective bars for actuation so that the desired shape can be obtained, without incurring violation in bar forces, through both a minimal number of actuators and minimum actuation in those actuators. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces (e.g., in a cable nearing slack).

Optimum control system for earthquake-excited building structures with minimal number of actuators and sensors

For vibration control of civil structures, especially large civil structures, one of the important issues is how to place a minimal number of actuators and sensors at their respective optimal locations to achieve the predetermined control performance. In this paper, a methodology is presented for the determination of the minimal number and optimal location of actuators and sensors for vibration control of building structures under earthquake excitation. In the proposed methodology, the number and location of the actuators are first determined in terms of the sequence of performance index increments and the predetermined control performance. A multi-scale response reconstruction method is then extended to the controlled building structure for the determination of the minimal number and optimal placement of sensors with the objective that the reconstructed structural responses can be used as feedbacks for the vibration control while the predetermined control performance can be maintained. The feasibility and accuracy of the proposed methodology are finally investigated numerically through a 20-story shear building structure under the El-Centro ground excitation and the Kobe ground excitation. The numerical results show that with the limited number of sensors and actuators at their optimal locations, the predetermined control performance of the building structure can be achieved.

Underactuated anthropomorphic hands: Actuation strategies for a better functionality

This paper aims to analyze the number of actuators as well as the actuation strategy for underactuated prosthetic hands. Two comprehensive analyses were performed for this purpose. 16 possible actuation strategies in five categories of one to five actuators were defined. Based on these 16 strategies two analyses were performed: grasp diversity and grasp functionality. In the first analysis, we defined a performance metric based on all possible grasps by the human hand, while in the second analysis only the top grasps with the highest frequency of usage were considered. By comparing the performance of these strategies we obtained some interesting results regarding the best actuation strategies for the under-actuated anthropomorphic hands. Such study can be useful for designers in the early stages of designing a prosthetic terminal, for deciding the number of actuators and how such actuators are allocated to the DOFs of the hand. In other words, this study shows which joints of the hands should be coupled together and driven by a single actuator, in order to get the best performance with minimum number of actuators. This is important for developing hands, which have a small number of actuators (i.e. less than 5 actuators), and thus benefit from a simple electromechanical structure.

Active optics with a minimum number of actuators

Abstract Optics for astronomy implies powerful developments of active and adaptive optics methods applied to instrumentation from X-rays to the near infrared for the design of telescopes, spectrographs, and coronagraph planet finders. This presentation particularly emphasizes the development of active optics methods. Highly accurate and remarkably smooth surfaces from active optics methods allow new optical systems that use highly aspheric and non-axisymmetric – freeform – surfaces. Depending on the goal and performance required for a deformable optical surface, elasticity theory analysis is carried out either with small deformation thin plate theory, large deformation thin plate theory, shallow spherical shell theory, or the weakly conical shell theory. A mirror thickness distribution is then determined as a function of associated bending actuators and boundary conditions. For a given optical shape to generate, one searches for optical solutions with a minimum number of actuators.

Active optics: deformable mirrors with a minimum number of actuators

We present two concepts of deformable mirror to compensate for first order optical aberrations. Deformation systems are designed using both elasticity theory and Finite Element Analysis in order to minimize the number of actuators. Starting from instrument specifications, we explain the methodology to design dedicated deformable mirrors. The work presented here leads to correcting devices optimized for specific functions. The Variable Off-Axis paraboLA concept is a 3-actuators, 3-modes system able to generate independently Focus, Astigmatism and Coma. The Correcting Optimized Mirror with a Single Actuator is a 1-actuator system able to generate a given combination of optical aberrations.

Overactuation: A solution for the accuracy–throughput speed contradiction in parallel axis positioning systems

In parallel axis positioning systems an accuracy–throughput speed contradiction is present. The configuration is often such that the minimum number of actuators from kinematic point of view is used. The mechanical system should possess sufficient stiffness but also low mass. Structural stiffness, and hence accuracy, is obtained at the cost of mass. In intermittent motion systems the moving mass should be minimized, because it limits the attainable acceleration and thus the throughput speed. This dynamic performance barrier can be shifted with additional parallel actuators. To enhance prudence in the initial design phase, knowledge about the opportunities and limitations of parallel axis systems is required. The basic dynamical aspects of parallel axis positioning systems, with a minimum and additional number of parallel actuators, are examined for beam and plate systems. The results of the numerical models are verified with an experimental plate system.

Study on Active Vibration Control for High-Speed Elevators

When elevators travel at high speed, horizontal vibrations of the car tend to occur due to guide rail deformations, deteriorating ride comfort. Therefore, several active control systems have been developed to reduce these vibrations. These systems consist of six actuators, which independently move the guide rollers. To reduce costs and installation time, it is necessary to develop a system with a minimum number of actuators and a simplified controller. We developed a system with only three actuators. The controller incorporates an H-infinity control design method for maintaining stability of the system when there is a change in load. Furthermore, from a practical point of view, it is important to reduce the order of the controller so that the time for on-site parameter tuning can be reduced. Therefore, we reduced the H-infinity controller to a P controller. We demonstrated that the maximum amplitude of vibrations of a car with active control system can be reduced to almost half the vibration amplitude without control.

Adjustable Mechanism for Walking Robots with Minimum Number of Actuators

Recent literature on walking robots deals predominantly with multi-degrees-of-freedom leg mechanisms and machines capable of adopting several gaits.This paper explores the other end of the spectrum suggesting mechanisms derived from a four bar coupler curve for a one degree of freedom walking robot.Simulation of the walk indicates that body of the robot is able to move with low variation in velocity.The best strategy for changing the gait to enable the robot to walk over obstacles and the effect of change in length of different links are explored to open up the possibility of a two degree of freedom walking robot with the capability of changing its gait,suitable as a low cost unit for several applications.Such rugged units would permit the use of an IC engine as the primary source of power and could be of utility in installations where electronics may not be functional.In simple walking machines the foot of a leg is usually required to trace a D shaped curve with respect to the chassis.In this paper we begin with a Hoecken mechanism capable of tracing such a curve.The foot is required to move parallel to itself and the same could be achieved using a six or eight link mechanism.A few such devices have been synthesized in this paper and their motion properties compared.The study also covers the possibility of providing adjustments to vary the step length and height of the foot's movement.