A compliant mechanism can be constructed by mounting springs at joints of a crank-slider linkage. Different mounting schemes bring changes in the stiffness performance. In this paper, a unified stiffness model is developed for a comprehensive analysis of the stiffness performance. With the model, stiffness behaviors of spring-loaded crank-slider mechanisms are analyzed. Influences of each individual spring on the overall performance are characterized. Based on the analysis, a potential application of constructing mechanisms with desired stiffness behavior in a simple implementation is proposed, which is demonstrated by a constant-torque mechanism and a variable stiffness mechanism.

Dielectric elastomers (DE) exhibit remarkable properties that make them stand out among other electroactive polymers. Various types of actuators based on DEs have been used in applications that include artificial muscles, Braille displays, and robotic joints. In particular, conical dielectric elastomer actuators (CDEAs) are very attractive due to their multiple degrees of freedom (DOF) and easiness of construction. In this study, an energy method is used to derive an improved mathematical model for a double-cone dielectric elastomer actuator (DCDEA) capable of predicting horizontal and rotational displacements. To create the model, a new variable is introduced into the equations, the azimuth angle. In addition, a new pattern of electrodes is proposed as a method for achieving five DOF using only half of the electrode connections of traditional DCDEAs. Experimental tests are carried out and used to validate the proposed model. Results show very close agreement. A limiting aspect of the proposed model is that it relies on two experimental correction coefficients. Nonetheless, the model derived provides a means to more accurately implement automatic control to robotic systems that use DCDEAs (work in progress).

Presented in this paper is a method for analysis and control of an actuation-redundant parallel mechanism requiring synchronization. The said mechanism is made up of two branches that are connected to drive a common end-effector with only one degree-of-freedom of motion. The two actuators must share the load exerted on the common end-effector during motion. The underlying problem is to synchronize the motion of the two actuators while balancing the forces on them so that the entire mechanism can move smoothly under the applied load on the end-effector. Due to the space limitation, the two branches are geometrically different leading to opposite force profiles for the two actuators. The proposed method combines the mechanism kinematics with force analysis. First, a closed-form solution is derived that relates the actuator strokes to the rotation angle of the end-effector. Second, a velocity relationship is obtained to relate the actuator velocities to the angular velocity of the end-effector. Third, a force relationship is established relating the actuator loads to the external load. Fourth, a control strategy is designed to synchronize the motion of the two actuators while maintaining the force balance between them to avoid the problem of motion mismatching and force fighting that could lead to the failure of the mechanism. A prototype was built and tested with the proposed method, which is also presented in this paper.

Surgical navigation of small lumens during surgery is a challenging task, requiring expert knowledge and dexterity. The challenge pertains to the manipulation of the distal tip (inside the patient) from the proximal end (outside the patient). Limitations in down-scaling tendon based manipulation have led our group to investigate Shape-Memory-Alloy, curvature-based actuation for small lumen navigation. We demonstrate two prototype designs with different approaches and characterize the deflection angles for use in surgical navigation. Nitinol wire was shape trained to memorize a particular curvature and assembled without using micro-fabrication techniques. By varying actuation voltage and control signal pulse width, we show controlled deflections ranging between 5° to 22°, which is applicable to surgical navigation. This concept improves distal control and makes the actuation of surgical actuators easier and safer. By varying voltage between 5.7 V to 6.3 V, we show temperature generated ranging between 37 °C to 43 °C, the force generated ranging between 0.015 N to 0.021 N experimentally and 0.01 N to 0.028 N theoretically.

Origami-based flexible, compliant and bio-inspired robots are believed to permit a range of medical applications within confined environments. In this article, we experimentally demonstrated an origami-inspired deployable surgical retractor integrating controllable stiffness mechanisms that can facilitate safe instrument-tissue interaction in comparison to their rigid counterparts. When controllable negative pressure is applied to the jammed origami structure of the retractor, it becomes more rigid, resulting in an increase in strength. Hence, we examine performances of retractor based on Daler-Rowney Canford paper (38 gsm) and sandpaper of 1000 grits. Experiments on the proposed retractor prototype showed sandpaper-based retractor can outperform paper-38-gsm retractor for tenting the facelift incision with the width of more than 9 cm. Though paper 38 gsm comprised of thin layers 16 times lesser in thickness than sandpaper, the experiments proved its performance comparable to the latter in the context of layer jamming (LJ). We leverage the advantage of LJ mechanism to change the retractor stiffness in an economical way, allowing the instrument to hold and separate the facelift incision to mitigate the likelihood of surgical complications. The retractor was equipped with a custom-made printed conductive ink-based fabric piezoresistive tactile sensor to assist clinicians with tissue-retractor interaction force information. The proposed sensor showed a linear relationship with the applied force and has a sensitivity of 0.833 N-1. Finally, cadaver experiments demonstrate an effective origami-inspired surgical retractor for assistance to surgeons and clinicians in near future.

Currently, flexible surfaces enabled to be actuated by robotic arms are experiencing high interest and demand for robotic applications in various areas such as healthcare, automotive, aerospace, and manufacturing. However, their design and control thus far has largely been based on “trial and error” methods requiring multiple trials and/or high levels of user specialization. Robust methods to realize flexible surfaces with the ability to deform into large curvatures therefore require a reliable, validated model that takes into account many physical and mechanical properties including elasticity, material characteristics, gravity, external forces, and thickness shear effects. The derivation of such a model would then enable the further development of predictive-based control methods for flexible robotic surfaces. This paper presents a lumped-mass model for flexible surfaces undergoing large deformation due to actuation by continuum robotic arms. The resulting model includes mechanical and physical properties for both the surface and actuation elements to predict deformation in multiple curvature directions and actuation configurations. The model is validated against an experimental system where measured displacements between the experimental and modeling results showed considerable agreement with a mean error magnitude of about 1% of the length of the surface at the final deformed shapes.

This study provides a type of soft vacuum-actuated rotary actuator. The structures in the actuator are based on different elastomeric structures that comprise a number of interacting elastic radial beams, elastic circumferential beams, and interconnected, deformable sector ring structure air chambers. When negative pressure is applied to the structure, the radial beams bend reversibly into serpentine shapes until adjacent circumferential beams contact each other. This bending results in a large change in the circumferential angle of the structure, but a smaller change in its radial width. Thus, the structure produces rotational motion in its circumferential direction. The design, fabrication, and mechanical analysis of the actuator are introduced, respectively. Moreover, finite element simulation analysis and experimental testing are carried out to study the corresponding relations between the air pressure, rotation angle, and force of the actuator. In addition, the stimulation results and the experimental results of the actuator are statistically analyzed by statistical product and service solutions ( spss ) statistical software. The test results of the experimental platform are highly correlated with the results of the finite element simulation.

Dynamics modeling is essential in the design and control of mechanical systems, the focus of the paper being redundantly actuated systems , which bring about special challenges. The authors resort to the natural orthogonal complement (NOC), based on an adaptation of screw theory , to derive the dynamics model. Benefiting from the elimination of the constraint wrenches, the NOC offers a simple, systematic alternative to the modeling of redundantly actuated mechanical systems. The optimum actuator-torque distribution is determined via Euclidean-norm minimization; then, by relying on the QR-decomposition, an efficient and robust method is produced to compute explicitly the right Moore–Penrose generalized inverse of the coefficient matrix. The methodology is illustrated via a case study involving a redundantly actuated parallel-kinematics machine with three degrees of freedom and four actuators.

High-concentration photovoltaic systems can provide power conversion efficiency that is nearly double that of conventional solar panels. Concentrating photovoltaics (CPV) cannot compete with fixed silicon panels for rooftop installations due to the complexity and cost of CPV two-axis pedestal tracking systems. Fixed optic designs have recently been proposed to have a transparent middle sheet with small, widely spaced, and highly efficient solar cells sandwiched between a fixed lenslet array on the top and a fixed reflector array on the bottom. Precision actuators position the middle sheet at the focal points of the lenslet/reflector array to microtrack the sun throughout the day. This paper discusses the kinematic design and control of shape memory alloy (SMA) actuators used for the first time in this solar microtracking application. SMA actuators have the potential to be less expensive, easier to integrate, and lower power than electric motors. The kinematic design maintains upper and lower bounds on wire tension to prevent failure and ensure reversible actuation, respectively. The SMA actuators under quasi-linearized proportional integral directive (PID) control can position the middle sheet with ± 7 mm of range in the vertical and horizontal directions while ensuring less than 1.9 µm of steady-state error in SMA actuator stroke. The middle sheet position and orientation errors, however, exceed 1 mm and 0.5 deg, respectively. These relatively large errors are due to flexibility in the suspension system, friction at wire supports, and large kinematic gains at extreme positions and indicate the need for middle sheet error measurement and feedback control.

Developing robotic systems for reducing the dependence of elderly on personal assistance is one of the most recent hot topics in robotics research. This paper proposes a multifunction mobility assistive device, which consists of an assisting parallel manipulator carried over an active walker. It is developed to interactively assist in various lower limb activities, namely, sit-to-stand, walking, bed or toilet to wheelchair transfer, and support in the upright position. The assisting parallel manipulator is constructed based on two of the nonconventional structure of the 3-R P R parallel manipulator. This structure offers kinematic decoupling between the position and orientation and free of singularity suitable workspace as well as high rigidity and payload capability. Kinematic, dynamic, and finite element analyses are performed to ensure the functionality of the device. A prototype of the device is constructed to verify the applicability of the device. The prototype is shown to be suitable for assisting subjects to stand up in a natural manner.

A robotic finger actuated by novel artificial muscles known as twisted and coiled polymer (TCP) muscles has been proposed as an inexpensive, yet high-performance component of a robotic hand in recent years. In this paper, the Euler–Lagrangian method coupled with an electro-thermo-mechanical model-based transfer function was used for the analysis of finger joints in the hand. Experiments were performed at three power magnitudes provided to the TCP muscles, and the output angular displacements of the index finger subtended corresponding to the power levels were measured. The measured input and output parameters were used for system identification. To elucidate how the new artificial muscle influences the finger motion, two types of numerical simulations were performed: force input simulation (FIS) using measured force as an input and power input simulation (PIS) using measured electrical power as an input. Results were quantified statistically, and the simulated data were compared with the experimental results. Sensitivity analysis was also presented to understand the effect of the mechanical properties on the system. This model will help in understanding the effect of the TCP muscles and other similar smart actuators on the dynamics of the robotic finger.

This paper describes the design and control of a novel hand exoskeleton. A subcategory of upper extremity exoskeletons, hand exoskeletons have promising applications in healthcare services, industrial workplaces, virtual reality, and military. Although much progress has been made in this field, most of the existing systems are position controlled and face several design challenges, including achieving minimal size and weight, difficulty enforcing natural grasping motions, exerting sufficient grip strength, ensuring the safety of the users hand, and maintaining overall user friendliness. To address these issues, this paper proposes a novel, slim, lightweight linkage mechanism design for a hand exoskeleton with a force control paradigm enabled via a compact series elastic actuator. A detailed design overview of the proposed mechanism is provided, along with kinematic and static analyses. To validate the overall proposed hand exoskeleton system, a fully integrated prototype is developed and tested in a series of experimental trials.

A typographical error first appearing in Equation A8 was cut and pasted into Equations A10 and A14. This error appears only in these equations as written in Appendix A.3. It does not affect the code used, results reported or paper conclusions.

This paper studies a novel fluid actuated system for a spherical mobile robot. The robot’s mechanism consists of two essential parts: circular pipes to lead spherical moving masses (cores) and an internal driving unit to propel the cores. The spherical shell of the robot is rolled by displacing the cores in the pipes filled with fluid. First, we describe the structure of the robot and derive its nonlinear dynamics using the D’Alembert principle. Next, we model the internal driving unit that actuates the core inside the pipe. The simulated driving unit is studied with respect to three important parameters—the input motor torque, the actuator size, and the fluid properties. The overall model of the robot is then used for analyzing motion patterns in the forward direction. Analytical studies show that the modeled robot can be implemented under the given design specifications.

Dielectric elastomer (DE), as a group of electro-active polymers, has been widely used in soft robotics due to its inherent flexibility and large induced deformation. As sustained high voltage is needed to maintain the deformation of DE, it may result in electric breakdown for a long-period actuation. Inspired by the bistable mechanism which has two stable equilibrium positions and can stay at one of them without energy consumption, two bistable dielectric elastomer actuators (DEAs) including a translational actuator and a rotational actuator are proposed. Both the bistable actuators consist of a double conical DEA and a buckling beam and can switch between two stable positions with voltage. In this paper, the analytical models of the bulking beam and the conical DEA are presented first, and then the design method is demonstrated in terms of force equilibrium and moment equilibrium principle. The experiments of the translational bistable DEA and the rotational bistable DEA are conducted, which show that the design method of the bistable DEA is effective.

A micropump sucker employs a gas film micropump to produce a negative pressure adhesion in a suction cup. In this study, a piezo-driven flexible actuator was developed based on a bridge-type mechanism as a vibrator for such a micropump film. The model of the flexible actuator under an external load is built based on an elastic model, and the displacement, driving force, and work efficiency are formulated in terms of the external loads, materials, and geometric parameters. The finite element method was used to verify this analytical model. An increase in the compliance of flexure hinges was found to improve the performances of the flexible actuator. The Young’s modulus of materials decides force performances and the effects of external loads. Based on the elastic analysis, the proposed flexible mechanism, made of silicon, was optimized to realize optimal output displacement in a compact size and employed in the prototype of a micropump sucker with a weight of 1.3 g that produced a maximum negative pressure of 2.45 kPa. It can hold on a weight of 1.4 g. When the inlet of the proposed sucker is open, it has the maximum flow rate of 4 ml/min.

Recent advancements in powered lower limb prostheses have appeased several difficulties faced by lower limb amputees by using a series-elastic actuator (SEA) to provide powered sagittal plane flexion. Unfortunately, these devices are currently unable to provide both powered sagittal plane flexion and two degrees of freedom (2-DOF) at the ankle, removing the ankle’s capacity to invert/evert, thus severely limiting terrain adaption capabilities and user comfort. The developed 2-DOF ankle system in this paper allows both powered flexion in the sagittal plane and passive rotation in the frontal plane; an SEA emulates the biomechanics of the gastrocnemius and Achilles tendon for flexion while a novel universal-joint system provides the 2-DOF. Several studies were undertaken to thoroughly characterize the capabilities of the device. Under both level- and sloped-ground conditions, ankle torque and kinematic data were obtained by using force-plates and a motion capture system. The device was found to be fully capable of providing powered sagittal plane motion and torque very close to that of a biological ankle while simultaneously being able to adapt to sloped terrain by undergoing frontal plane motion, thus providing 2-DOF at the ankle. These findings demonstrate that the device presented in this paper poses radical improvements to powered prosthetic ankle-foot device (PAFD) design.

Active exoskeletons have capacity to provide biologically equivalent levels of joint mechanical power, but high mass of actuation units may lead to uncoordinated walking and extra metabolic consumption. Active exoskeletons normally supply assistance directly during push-off and have a power burst during push-off. Thus, the requirements on power of motors are high, which is the main reason for the high mass. However, in a muscle-tendon system, the strategy of injecting energy slowly and releasing quickly is utilized to obtain a higher peak power than that of muscle alone. Application of this strategy of peak power amplification in exoskeleton actuation might lead to reductions of input power and device mass. This paper presents an ankle exoskeleton which can accumulate the energy injected by a motor during the swing phase and mostly the stance phase and then release it quickly during push-off. An energy storage and release system was developed using a four-bar linkage clutch. In addition, evaluation experiments on the exoskeleton were carried out. Results show that the exoskeleton could provide a high power assistance with a low power motor and reduced the requirement on motor power by 4.73 times. Besides, when walking with the exoskeleton, the ankle peak power was reduced by 25.8% compared to the normal condition. The strategy which imitates the working pattern of the muscle-tendon system leads to a lightweight and effective exoskeleton actuation, and it also supplies ideas for the designs of lightweight actuators that work discontinuously in other conditions.

This paper develops a geometric method to estimate the error space of 3-DOF planar mechanisms with the Minimum Volume Ellipsoid Enclosing (MVEE) approach. Both the joint clearances and actuator errors are considered in this method. Three typical planar parallel mechanisms are used to demonstrate. Error spaces of their serial limbs are analyzed. Thereafter, limb-error-space-constrained mobility of the manipulator, namely, the manipulator error space is analyzed. The MVEE method has been applied to simplify the constraint modeling. A closed-form expression for the manipulator error space is derived. The volume of the manipulator error space is numerically estimated. The approach in this paper is to develop a geometric error analysis method of parallel mechanisms with clear algebraic expressions. Moreover, no forward kinematics computations have been performed in the proposed method, in contrast to the widely used interval analysis method. Although the estimated error space is larger than the actual one, because the enclosing ellipses enlarge the regions of limb error space, the method has an attractive advantage of high computational efficiency.

We present a novel 4-DOF (degrees of freedom) parallel robot designed for five-axis micromachining applications. Two of its five telescoping legs operate simultaneously, thus acting as an extensible parallelogram linkage, and in conjunction with two other legs control the position of the tooltip. The fifth leg controls the tilt of the end-effector (a spindle), while a turntable fixed at the base of the robot controls the swivel of the workpiece. The robot is capable of tilting its end-effector up to 90 deg, for any tooltip position. In this paper, we study the mobility of the new parallel kinematic machine (PKM), describe its inverse and direct kinematic models, then study its singularities, and analyze its workspace. Finally, we propose a potential mechanical design for this PKM utilizing telescopic actuators as well as the procedure for optimizing it. In addition, we discuss the possibility of using constant-length legs and base-mounted linear actuators in order to increase the volume of the workspace.