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The Hessian matrix, one of the most pivotal parts in a robotic system's acceleration model, is a prerequisite for dynamic modeling and control of parallel robots. Aimed at providing a straightforward and effective way for modeling, design, and control of parallel robots, a new approach to formulate the Hessian matrix using the finite and instantaneous screw theory is presented in this paper. The new approach is generalizable in that it can be used to formulate the Hessian matrix of any parallel robot in a simple and concise manner. It also provides a theoretical foundation for the dynamic control of industrial robotic systems with parallel structures. The new approach is verified through comparison with the traditional exponential matrix method. The Exechon parallel robot and a hybrid serial-parallel robot are used as examples to further detail the procedures of this approach. The acceleration model formulated in this paper is closely related with the topological and parametric models, resulting in a unified mathematical framework for modeling and control of parallel robots. [ABSTRACT FROM AUTHOR]

In this paper, a new-type of mechanical-motion-rectifier-based energy harvesting shock absorber using a ball-screw mechanism and two one-way clutches is proposed to replace conventional oil dampers in vehicle suspensions. The proposed energy-harvesting shock absorber can work as a controllable shock absorber as well as an energy harvester. The challenge to harvest energy from reciprocating suspension vibration is solved by integrating a mechanical motion rectifier in the proposed design, which can convert reciprocating vibration into unidirectional rotation of a generator. As a result, the proposed shock absorber achieves high energy-harvesting efficiency by enabling the generator to rotate at a relatively steady speed during irregular vibrations and improves system reliability by reducing impact forces in transmission gears. In addition, the backlash of the proposed shock absorber is significantly reduced due to the use of the ball-screw mechanism, which further increases transmission durability and efficiency. Lab and field tests are carried out to experimentally characterize the proposed energy-harvesting shock absorber. The field testing results show that, when the modified vehicle is driven on a paved road at 40 mph, the proposed energy-harvesting shock absorber is able to reduce the root-mean-square value of chassis acceleration by 11.12% over the oil shock absorber and simultaneously harvest an average power of 13.3 W for a representative period of 8 s. [ABSTRACT FROM PUBLISHER]

This paper presents a lightweight (328 g) anthropomorphic robot hand that can exert a large grasping force. We propose a mechanism combining flexion drives and a force-magnification drive for a cable-driven multifingered robot hand. The flexion drive consisting of a feed screw enables quick finger motion, and the force-magnification drive, consisting of an eccentric cam, a bearing, and a pulley, enables a firm grasp. This paper also proposes a 3-D linkage for the thumb. This linkage consists of four links and is driven by a feed screw. It can oppose to a large force exerted by the force-magnification drive. These mechanisms are compact enough to be installed in the developed lightweight hand. We experimentally verify that the maximum fingertip force of the hand exceeds 20 N and that the thumb can hold a large force of 100 N. The time to fully close the hand using the flexion drives is 0.47 s. After the fingers make contact with an object, the time to achieve a firm grasp using the grasp-magnification drive is approximately 1 s. [ABSTRACT FROM PUBLISHER]

This paper presents a novel piezoelectrically actuated dual-axis micromanipulator with an asymmetric compliant structure. The mechanical design of the micromanipulator is first presented. A novel guiding bridge-type mechanism was proposed and utilized in the left part of the micromanipulator to improve the dynamic performance of the micromanipulator. The analytical model has been established based on the pseudorigid-body model and matrix-based compliance modeling method. The kinematic and the precision of the micromanipulator have been analyzed, and the input and output couplings have been investigated. The prototype of the micromanipulator has been fabricated by wire electrodischarge machining. Then, open-loop experimental tests have been performed. The experimental results match well with the analytical calculation, and the amplification ratios are 11.12 and 4.64 for the left part and right part, respectively. Proportional-integral controller has been used to regulate the output displacement and grasping force, and a series of closed-loop experiments have been conducted to investigate the performance of the micromanipulator. The results show that the position resolution for both the right and left parts is 0.15 μm, and the force resolution is 4 mN. [ABSTRACT FROM AUTHOR]

Robotic ankle prostheses can imitate the biomechanical function of intact legs at the cost of a larger weight and size compared to conventional passive prostheses. Unfortunately, increased weight and size negatively affect comfort and socket stability, ultimately limiting their clinical viability. Alternatively, a nonbackdrivable transmission system can be used to actively regulate the ankle position during nonweight bearing activities only. This semiactive design can be made smaller and lighter as a result of the lower actuation power requirements. However, the transmission system must withstand high loads during stance and standing. Thus, available semiactive prostheses are still significantly heavier and have a larger build height than passive ankle prostheses. In this paper, we present the design, development, and validation of a semiactive ankle prosthesis with a nonbackdrivable cam-follower mechanism designed to lower the load on moving components and align with the foot longitudinally as necessary to reduce the prosthesis weight and size. The proposed ankle mechanism is ∼50% shorter, has ∼40% wider range of motion (ROM), and is estimated to be ∼27% lighter than available semiactive prostheses. Experiments with a transtibial subject show that the semiactive prosthesis can increase foot clearance up to 142% and reduce the load on the residual limb as low as 32% compared to passive prostheses. [ABSTRACT FROM AUTHOR]

This paper studies the stability control of a target towed by a space-tug via a tether in orbital transfer. The attitude of the towed target is controlled by thrust regulation at the tug with the consideration of the coupling effect between the attitudes of the tug and towed target and the motion of the flexible and elastic tether. A model-based control scheme is proposed, where the tug and towed target are assumed as rigid bodies and the tether is approximated as a series of extensible but incompressible rods connected by spherical hinges. The governing equations of motion of the coupled rigid–flexible multibody system are derived based on the recursive dynamics algorithm. The attitude motion of the tug with the presence of tether tension disturbance is controlled by a simple proportional–derivative torque controller. The attitude motion of the towed target and the elongation oscillation of the tether are stabilized simultaneously via the tether tension by regulating the thrust at the tug. The thrust control is achieved by first designing an optimal trajectory considering the system constraints based on a reference model, and then the trajectory is tracked by a robust global terminal sliding-mode controller with the consideration of thrust saturation and tether slackness avoidance. Finally, numerical simulation is carried out to demonstrate the effectiveness of the proposed attitude control law based on the thrust regulation. [ABSTRACT FROM AUTHOR]

This paper discusses design and control of a prismatic series elastic actuator with high mechanical power output in a small and lightweight form factor. A design is introduced that pushes the performance boundary of electric series elastic actuators by using high motor voltage coupled with an efficient drivetrain to enable large continuous actuator force while retaining speed. Compact size is achieved through the use of a novel piston-style ball screw support mechanism and a concentric compliant element. Generic models for two common series elastic actuator configurations are introduced and compared. These models are then used to develop controllers for force and position tracking based on combinations of PID, model-based, and disturbance observer control structures. Finally, our actuator’s performance is demonstrated through a series of experiments designed to operate the actuator at the limits of its mechanical and control capability. [ABSTRACT FROM PUBLISHER]

Spinal orthopedic surgery is one of the typical high-risk surgeries. During the surgery, bone screws need to be inserted into the narrower vertebral pedicles and any failures in the screw-path-drilling process will directly hurt the important nerves and vessels of the patient. In this paper, a robotic spinal surgical system (RSSS) for assisting pedicle screw insertion surgery is proposed. The novel structural configuration of the RSSS can balance the gravity effects of the arms, and the workspace envelope of the RSSS can better fit the requirements of spinal surgery. The procedure of the screw insertion operation with the proposed RSSS is presented. To simulate the hand feel of the surgeon in surgical operations, a real-time force-sensing algorithm is developed for the screw-path-drilling process using a spherical or a twist drill. With the force sensing, five key states, including the initial state, the outer cortical state, the cancellous state, the transitional state, and the inner cortical state, are recognized. In particular, the clear recognition of the transitional zone between the cancellous bone and the inner cortical bone is very important as the drilled screw path ends in this zone. State recognition with force sensing can effectively improve the quality of the screw paths so as to enhance the quality of the spinal surgery. Experiments were carried out to verify the state recognition effects of the pedicle drilling process with force sensing. [ABSTRACT FROM PUBLISHER]

This paper presents a high-sensitivity triaxial catheter distal force sensor for cardiac ablation through the combined use of a force-sensitive flexure and fiber Bragg grating (FBG) sensing. A miniature force-sensitive flexure has been designed as the catheter tip, and it has an elliptical hinge with a symmetric structure for two-axial transverse force sensing and employs a pair of U-type beam slots above the hinge to sense the $z$ -direction force. Five optical fibers embedded with an FBG element each have been integrated with this flexure to detect the force-induced strain on the flexure. Each fiber is configured as a tightly suspended status with its two ends fixed, ensuring to achieve an improved sensitivity. The theoretical force–deformation relationship has been derived, and the approach for decoupling force and temperature has been presented. Finite element modeling based simulations have been performed to support the parametric design and improvement of the flexure structure. Static calibration experiments demonstrate the excellent resolution values of 2.13 and 2.52 mN for both transverse directions within –1 to 1 N, and 23.12 mN for the axial direction within 0–2 N. The linearity, repeatability, and hysteresis errors have been characterized with less than 5.3%, demonstrating the stable performance. The force and temperature can be effectively decoupled and detected with a temperature less than 60 °C. Dynamic loading experiments at different spatial angles and in vitro experiments in a silicone aortic vessel phantom have been carried out to further validate the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

This paper presents a three-fingered, eight-DOF hand, 100 N Hand II, which can exert a grasping force of 100 N. A force-magnification drive, which can maintain a large grasping force without energy consumption, allows the hand to exert such large grasping force, and a high-speed driving mechanism enables all joints to perform high-speed motions of over 400^\circ/s. In our previous prototype (100 N Hand I), a screw and nut mechanism was used to implement force magnification. The linear motion of this mechanism was translated to rotational joint motion via a linkage mechanism, producing a relatively small motion range for each joint and with large palm dimensions. 100 N Hand II employs a worm gear instead of a screw and nut mechanism, so it can magnify the torque at an arbitrary joint angle. This improved force-magnification drive increases the motion range of each joint and reduces the palm size. The force and speed are confirmed experimentally. [ABSTRACT FROM PUBLISHER]

This paper presents a novel two-dimensional vibration-assisted compliant cutting system (2-D VCCS) to be used on conventional machines for generating textured surfaces with uniform and accurate topography. The proposed system is specifically designed to be capable of delivering high-amplitude vibrations with decoupled guidance at the tool tip, while keeping high resistance to cutting forces during the texturing process. The matrix-based compliance modeling method is adopted for compliance and dynamic modeling of the 2-D VCCS. With optimized structural parameters, the model is validated by theoretical and finite element analysis. On-machine performance tests were conducted to identify the vibration amplitudes, stiffness, and frequency responses of the device. Finally, various complex textured surfaces were uniformly and accurately generated by the high-performance 2-D VCCS using a V-shaped diamond tool. The actually textured surfaces were evaluated and shown that they closely match the theoretically predicted surfaces based on the in-process monitored parameters, demonstrating the great potential of the 2-D VCCS to create functional surfaces for industrial products. [ABSTRACT FROM PUBLISHER]

In stick-slip positioning, friction between the stick-slip surfaces plays a critical role in positioning accuracy. Positioning performance varies when the load to drive changes. In this paper, by using a form-closed cam, the driving unit is separated from the moving unit to eliminate load influence. The stage is capable of operating in either a stepping mode or a scanning mode. Numerical modeling was conducted to analyze the static and dynamic characteristics of the stage design. In experiments, a number of parameters were tested on the constructed stage, and positioning performance was measured via laser-doppler vibrometry. Experimental results demonstrate that in the stepping mode, the stage has a travel range of 2 mm with incremental step sizes ranging from 30 nm to 2.3 μm. In the scanning mode, the stage has a positioning resolution of 1.15 nm. The measured results also confirm that load variations on the stage have little influence on contact friction force and positioning performance. [ABSTRACT FROM PUBLISHER]

This paper presents a method for designing a controller that achieves the best positioning performance while maximizing the energy efficiency of a redundantly actuated hybrid feed drive. A two-degree-of-freedom controller, consisting of a feedforward (FF) controller for tracking and a feedback (FB) controller for regulation, is assumed. It is shown that the ideal FF controller, which achieves perfect tracking with maximum efficiency, is not always stable. Therefore, a method for designing a stable FF controller that achieves perfect tracking with near optimal efficiency is proposed. Furthermore, the optimal relationship between FB control inputs, which guarantees maximum efficiency for any specified regulation performance, is derived. Two approaches for using the derived optimal relationship to synthesize a FB controller that achieves the best positioning performance while maximizing efficiency are proposed. Simulations and machining experiments are conducted to demonstrate the effectiveness of the proposed energy-efficient FF and FB controller design methods. Significant improvements in energy efficiency (without sacrificing positioning performance) are reported. [ABSTRACT FROM PUBLISHER]

This paper presents the design, optimization, and computational and experimental performance evaluations of a passively actuated, monolithic, compliant mechanism. The mechanism is designed to be mounted on or built into any precision positioning stage, which produces three degree-of-freedom (3-DOF) planar motions. It transforms such movements into linear motions, which can then be measured using laser interferometry-based sensing and measurement techniques commonly used for translational axes. This methodology reduces the introduction of geometric errors into sensor measurements, and bypasses the need for increased complexity sensing systems. A computational technique is employed to optimize the mechanism's performance, in particular, to ensure the kinematic relationships match a set of desired relationships. Computational analysis is then employed to predict the performance of the mechanism throughout the workspace of a coupled positioning stage, and the errors are shown to vary linearly with the input position. This allows the errors to be corrected through calibration. A prototype is manufactured and experimentally tested, confirming the ability of the proposed mechanism to permit measurements of 3-DOF motions. [ABSTRACT FROM PUBLISHER]

Precision positioning stages with large strokes and high positioning accuracy are attractive for high-performance micro/nano manufacturing. This paper presents the dynamic design and characteristic investigation of a novel XY micropositioning stage. First, the mechanism of the stage was introduced. The XY stage was directly driven by two linear motors, and the X- and Y-axes kinematic decoupling was realized through a novel flexible decoupling mechanism based on the flexure hinges and preloaded spring. The dynamic model of the XY stage was established, and the influences of the rotational stiffness of the flexure hinge and the initial positions of the working table on the dynamic rotation of the positioning stage were investigated. The stiffness and geometric parameters of the flexure hinges were determined at the condition that the angular displacements of the working table were within ±0.5° with a motion stroke of ±25 mm. Finally the stage performance was investigated through simulation and experiments, and the X- and Y-axes step responses, the rotation angle, and positioning accuracy of the stage were obtained. The results show that the stage exhibits good performance and can be used for micro/nano manufacturing. [ABSTRACT FROM PUBLISHER]

This paper presents the development of a novel regenerative shock absorber sized for a passenger car suspension system. The shock absorber includes a simple and highly efficient motion converter called a two-leg mechanism , a planetary gearhead, and a brushless three-phase rotary machine. The design and analysis of the regenerative shock absorber are presented by considering the dynamics and efficiency of the electromechanical device. The performance of the regenerative damper is evaluated under sinusoidal excitation inputs for typical amplitudes and frequencies in a vehicular suspension system. Experimental results show that a damping coefficient of $1720$ N$\cdot$s/m can be achieved by controlling the external loads. Furthermore, a mechanical energy conversion efficiency between 0.71 and 0.84 is achieved, which is considerably higher than other mechanisms reported in the literature, such as ball screw, rack-and-pinion, and linear mechanisms. [ABSTRACT FROM PUBLISHER]

This paper presents a novel microgripper mechanism for micromanipulation and assembly. The microgripper is driven by a piezoelectric actuator, and a three-stage flexure-based amplification has been designed to achieve large jaw displacements. The kinematic, static and dynamic models of the microgripper have been established and optimized considering the crucial parameters that determine the characteristics of the microgripper. Finite element analysis was conducted to evaluate the characteristics of the microgripper, and wire electro discharge machining technique was utilized to fabricate the monolithic structure of the microgripper mechanism. Experimental tests were carried out to investigate the performance of the microgripper and the results show that the microgripper can grasp microobjects with the maximum jaw motion stroke of 190 μm corresponding to the 100-V applied voltage. It has an amplification ratio of 22.8 and working mode frequency of 953 Hz. [ABSTRACT FROM PUBLISHER]

This paper introduces a new type of linear actuator using the electromagnetic attractive force, which enables a submillimeter stroke. In general, actuation by the electromagnetic attractive force causes a tradeoff problem between the thrust force and the stroke because the thrust force depends on the gap between the electromagnet and the armature; an increase in the gap (stroke) drastically degrades the thrust force. To realize a submillimeter stroke while retaining a high thrust force, a structure that adopts a displacement amplification mechanism is proposed, which is often used to expand the stroke of a piezoelectric actuator. First, the electromagnetic attractive force is theoretically examined with and without displacement amplification. We verify that displacement amplification could create a higher thrust force and energy efficiency over a certain displacement. On the basis of this examination, a prototype actuator is designed, and the driving principle is illustrated. Further, an analytical model of the proposed actuator is developed for control and performance estimation. Several fundamental experiments with a developed actuator are performed in order to reveal the potential of the proposed actuator. The performance evaluations show that the maximum stroke is approximately 450 $\mu$m and a bandwidth greater than 300 Hz can be realized, and more a time constant is approximately 2 ms for a stroke of 450 $\mu$m. In addition, the experimental results were compared with the simulation results calculated from the analytical model to verify whether the prototype drives predictably according to the proposed concept under a dynamic situation. These results demonstrate that the proposed actuator enables good actuation performance, and it implies that there are tremendous advantages from the viewpoints of manufacturing, assembly, control, etc. [ABSTRACT FROM PUBLISHER]

In this paper, a tilting-type balancing mobile robot platform is investigated for enhancing lateral stability. In addition to pitch, yaw, and straight motion by the conventional two-wheeled inverted pendulum mechanism, it can generate roll and vertical motion by an additional tilting mechanism. The static force analysis shows that body separation tilting is more advantageous in power consumption than single body tilting, specifically when the payload to body weight is relatively small. Some design considerations are given for the determination of body structure and actuator powers. For the dynamic modeling, the titling balancing platform is assumed as a three-dimensional inverted pendulum with moving base and the nonlinear equation of motion is derived in terms of Kane's method. Then, a velocity/posture control loop is constructed, where the tilt angle reference is naturally generated according to the centrifugal force variation in following a circular path. Experimental results are given to validate the proposed mobile platform with the tilting control strategy. [ABSTRACT FROM PUBLISHER]

Ball-screw-driven stages are widely used in industry for long-range and high-precision fabrication. One of the main difficulties in dealing with high-precision motion control is the nonlinear friction, which originates at elastic deformation of the mechanical components. In this paper, first, a novel mechanical model of a ball-screw-driven stage is proposed to analyze the elastic deformation dynamics under various motion conditions. It is achieved that the mechanical deformation characteristic of fast motions differs from the case of slow motions in the zero-speed region, and therefore, performing friction compensation should take the motion conditions into account. Then, based on this observation, a sinc-function-based friction compensation method for slow motions including both reverse motions and nonreverse motions and a Sigmoid-function-based friction compensation method for fast reverse motions are proposed to improve the control performance. Thanks to the very few parameters, the proposed methods can save much trouble in design and maintenance and are particularly suitable for control purposes. Finally, the advantages of the proposed methods are evaluated by experiments. [ABSTRACT FROM PUBLISHER]

This paper proposes a parallel structure of a feedback controller for the ball–screw drive systems which have significant dynamic variations during operations. The controller consists of two controllers with two different objectives. One controller aims at moving the workpiece table so that its position tracks reference trajectories with high speed and high accuracy. The other controller is for suppressing the structural vibration caused by the cutting force disturbance around system’s resonant frequencies. To take into account the resonant modes’ variations which are peculiar to ball–screw drives, a gain-scheduled controller is utilized as the vibration suppression controller. Advantages of the proposed controller structure in the ball–screw drive control application are discussed. It is experimentally demonstrated that the controller with the parallel structure is effective in achieving high performance in both trajectory tracking and cutting force disturbance rejection. [ABSTRACT FROM PUBLISHER]

Large displacement compliant joints can substitute traditional kinematic pairs in robotic articulated structures for increasing ease-of-assembly, robustness, and safety. Nonetheless, besides their limited motion capabilities, compliant joints might be subjected to undesired spatial deformations which can deteriorate the system stability and performance whenever a low number of control inputs is available. In all these cases, it is convenient to select/design joint morphologies which enable a selectively compliant behavior, i.e., a low stiffness along a single desired direction. Within this context, this paper outlines an engineering method for quantifying the joint’s selective compliance by means of local and global performance indices. The approach is validated by comparing two beam-like flexures whose analytic solution is known from the literature. Finally, two joint morphologies, previously employed in the fabrication of robotic/prosthetic hands, are critically compared on the basis of the proposed criteria. [ABSTRACT FROM PUBLISHER]

This paper presents the development of a novel energy-regenerative suspension mechanism. The system consists of a mass-spring unit coupled with an algebraic screw kinematic pair, a rotary permanent magnet synchronous generator (PMSG), and a three-phase boost charger connected to a battery. The algebraic screw converts the translational vibration into a reciprocating rotary motion which drives the PMSG through a planetary gearhead. A pulse-width-modulated three-phase boost converter is then used to convert the energy generated by the rotary machine into battery charge. To this end, a control and switching algorithm is utilized that makes the battery appear as a pseudo-resistor across the terminals of the rotary machine. Introducing this pseudo-resistive characteristic across the machine produces the same effect as mechanical damping with an energy regenerative function. The design and analysis of the regenerative suspension mechanism are presented by considering the dynamics of the electromechanical device, parameters of the suspension system, and the base excitation input profile. Experimental results are presented that evaluate performance of the proposed regenerative damper on a small-scale suspension system, which demonstrate the feasibility of building energy-regenerative dampers. [ABSTRACT FROM PUBLISHER]

This paper presents a new type of 4-degree-of-freedom (DOF) robotic surgical instrument for a minimally invasive surgical robot system. The forceps wrist mechanism was designed here on the basis of the 3-DOF parallel structure with three prismatic–spherical–revolute kinematic chains. The pitch and yaw motions of the moving platform generated the wrist rotational motions of the forceps. The axial translation of the parallel mechanism was converted into the forceps grasp motion by an inversion of the slider-crank mechanism. Furthermore, for a more dexterous movement of the forceps, a full revolution of the forceps for the axial rotation is also possible with the instrument. While the proposed instrument realized all the required DOFs of a forceps, the parallel structure of the wrist and the driving mechanism that was designed using only rod elements made the proposed instrument more reliable and rigid than other wire-driven instruments. The kinematic constraints and inverse kinematics of the proposed instrument were derived. Furthermore, the screw-based Jacobian was formulated geometrically, and the static force relation and the linear constraints on a twist were derived. Finally, a prototype of the proposed instrument with a diameter of \8 mm was introduced, and the performance of the prototype was verified through several experiments. [ABSTRACT FROM PUBLISHER]

This paper describes the development of an automated dynamometer to characterize brushed direct current motors. The unique mechanical design allows the testing of a wide range of motor sizes. The motor under test is subjected to a given pulse width modulated voltage signal and position, current, and voltage measurements are simultaneously recorded from the integrated sensor suite. An electromechanical motor model is developed by combining the voltage and torque balance equations of the system. A least-squares algorithm is used to estimate the parameters that best fit the observed data to the specified gray box model. The system retains a low cost by using off-the-shelf electronics and cheaply fabricated mechanical parts. The inertia and friction of the system are carefully modeled, removing the need for an expensive torque sensor. The mechanical drawings, electrical schematics, and software are open source and freely available for download. Consistent parameter estimates from a set of high-tolerance and well-documented identical motors demonstrate the accuracy and precision of the system. [ABSTRACT FROM PUBLISHER]

In this paper, a new actuator with adjustable stiffness (AwAS) is presented. AwAS is capable of controlling the position and stiffness of a joint, independently. The proposed actuator can regulate the joint stiffness through a wide range with minimum energy consumption by means of a small motor. This is possible due to its novel mechanical configuration that achieves the stiffness regulation not through the control of spring pretension (as in most of the existing variable stiffness joints) but by using the variable lever arm principle. The regulation of the lever arm length is achieved through the displacement of the spring elements. An important consequence of this mechanism is that the displacement needed to change the stiffness is perpendicular to the forces generated by the spring. This helps to reduce the energy/power required to regulate the stiffness. It is experimentally shown that AwAS is capable of minimizing energy consumption through exploiting the natural dynamics in real time for both fixed and variable frequency motions. [ABSTRACT FROM PUBLISHER]

In this paper, we report on the design, modeling, and experimental testing of a piezoelectric-driven microgripper making use of both an integrated gripping force sensor and an integrated tip displacement sensor. In the developed microgripper, a stack piezoelectric ceramic actuator is used to simultaneously obtain the tip displacement and the gripping force. A novel monolithic compliant mechanism is proposed to act as the microdisplacement transmission mechanism to obtain the large tip displacement and to provide the possibility of integrating both the gripping force sensor and the tip displacement sensor into the microgripper. The relationship between the gripping force, tip displacement, input force, and input displacement of the piezoelectric-driven microgripper and the dynamic model are established using the pseudorigid-body-model method. The characteristics of the developed microgripper are tested and the case of gripping an optical fiber is presented. The experimental results indicate that: 1) the theoretical model for the developed microgripper matched well with the measured results; 2) the integrated gripping force sensor and tip displacement sensor could accurately measure the gripping force and tip displacement; 3) the developed microgripper could achieve a displacement magnification of 16.0 \times with respect to the stack piezoelectric ceramic actuator to realize the large tip displacement with high resolution but is also able to possess the parallel movement of its gripping jaws and the constant displacement magnification. [ABSTRACT FROM PUBLISHER]

This paper presents mechanism and controller design procedures of a new piezoactuated flexure XY stage for micro-/nanomanipulation applications. The uniqueness of the proposed stage lies in that it possesses an integrated parallel, decoupled, and stacked kinematical structure, which owns such properties as identical dynamic behaviors in X and Y axes, decoupled input and output motion, single-input-single-output (SISO) control, high accuracy, and compact size. Finite element analysis (FEA) was conducted to predict static performance of the stage. An XY stage prototype was fabricated by wire electrical discharge machining (EDM) process from the alloy material Al7075. Based on the identified plant transfer function of the micropositioning system, an H_\infty robust control combined with a repetitive control (RC) was adopted to compensate for the unmodeled piezoelectric nonlinearity. The necessity of using such a combined control is also investigated. Experimental results demonstrate that the H_\infty plus RC scheme improves the tracking response by 67% and 28% compared to the stand-alone H_\infty for 1-D and 2-D periodic positioning tasks, respectively. Thus, the results illustrate the effectiveness of the proposed mechanism design and control approach. [ABSTRACT FROM PUBLISHER]

This paper presents the design of an electrically actuated, proportional brake that provides a significantly greater torque-to-weight ratio than a magnetic particle brake (MPB) (considered a benchmark of the state of the art) without sacrificing other characteristics, such as dynamic range, bandwidth, or electrical power consumption. The multidisc brake provides resistive torque through a stack of friction discs, which are compressed by a dc-motor-driven ball screw. Unlike nearly all other proportional brakes, which operate in a normally unlocked mode, the brake presented here is designed such that it may be configured in either a normally unlocked or normally locked mode. The latter enables lower electrical energy consumption and added safety in the event of electrical power failure in certain applications. Following the device description, experimental data are presented to characterize the performance of the brake. The performance characteristics are subsequently compared to those of a commercially available MPB of comparable size. [ABSTRACT FROM PUBLISHER]

This paper presents the design analysis fabrication and testing of a high-bandwidth piezo-driven parallel kinematic nanopositioning XY stage. The monolithic stage design has two axes and each axis is composed of a doubly clamped beam and a parallelogram hybrid flexure with compliant beams and circular flexure hinges. The doubly clamped beam that is actuated by a piezoelectric actuator acts as a linear prismatic axis. The parallelogram hybrid flexures are used to decouple the actuation effect from the other axis. The mechanism design decouples the motion in the X- and Y-directions and restricts parasitic rotations in the XY plane while allowing for an increased bandwidth with linear kinematics in the operating region. Kinematic and dynamic analysis shows that the mechanical structure of the stage has decoupled motion in XY-direction while achieving high bandwidth and good linearity. The stage is actuated by piezoelectric stack actuators, and two capacitive gauges were added to the system to build a closed-loop positioning system. The results from frequency tests show that the resonant frequencies of the two vibrational modes are over 8 kHz. The stage is capable of about 15 μm of motion along each axis with a resolution of about 1 nm. Due to parallel kinematic mechanism design, a uniform performance is achieved across the workspace. A PI controller is implemented for the stage and a closed-loop bandwidth of 2 kHz is obtained. [ABSTRACT FROM PUBLISHER]

This article presents a directly 3-D printed soft monolithic robotic finger with embedded soft pneumatic sensing chambers (PSC) as position and touch sensors. The monolithic finger was fabricated using a low-cost and open-source fused deposition modeling 3-D printer that employs an off-the-shelf soft and flexible commercially available thermoplastic polyurethane. A single soft hinge with an embedded PSC was optimized using finite element modeling and a hyperelastic material model to obtain a linear relationship between the internal change in the volume of its PSC and the corresponding input mechanical modality, to minimize its bending stiffness and to maximize its internal volume. The soft hinges with embedded PSCs have several advantages, such as fast response to very small changes in their internal volume (∼0.0026ml/°), linearity, negligible hysteresis, repeatability, reliability, long lifetime, and low power consumption. Also, the flexion of the soft robotic finger was predicted using a geometric model for use in real-time control. The real-time position and pressure/force control of the soft robotic finger were achieved using feedback signals from the soft hinges and the touch PSC embedded in the tip of the finger. This article contributes to the development of seamlessly embedding optimized sensing elements in the monolithic topology of a soft robotic system and controlling the robotic system using the feedback data provided by the sensing elements to validate their performance. [ABSTRACT FROM AUTHOR]

Due to limitations in the fabrication technology, the large aperture space optical mirror is always spliced into several small segments rather than fabricated monolithically. To guarantee the imaging quality of the system, each segment needs to be aligned at micron-level precision with millimeter-level range. For this purpose, a PZT actuated six-axis high-precision positioning system, which consists of three serially connected parallel mechanisms is proposed in this article. Compared with previous 6-DOF positioning solutions, such as a Stewart platform, the proposed design features a relatively compact structure and straightforward kinematics. To realize long stroke and fine resolution simultaneously, bridge-type amplifiers are employed to enhance the stroke of the PZT actuation, and the flexure hinges are utilized to eliminate friction and backlash. The performance of the amplifier under two kinds of external loads are analyzed so that the amplifiers could be designed according to the application conditions. Furthermore, it can be found that the displacement sensors must be employed at the output end of the actuation module to eliminate the input coupling that commonly exists in the compliant mechanisms. The feasibility of the design is validated by finite-element analysis and experiment study. The maximum stroke is 2.1 mm in the Z-axis, and the finest resolution is 0.5 μm in X- and Y-axis. [ABSTRACT FROM AUTHOR]

An origami-structured compliant actuator (OSCA) is developed for human–robot interaction, in which adequate power output, as well as safety, is emphasized under a limited power supply. The OSCA inherits the safety feature from soft actuators, while, at the same time, it ensures that expansion in off-axis directions is converted to on-axis moment. The kinematic singularity originating from its actuator design gives rise to a significant mechanical advantage over certain ranges of motion. The compressibility of airflow within the actuator essentially provides both backdriveability and elasticity, the latter contributing to increasing the actuator's power output in the same way as does a series elastic actuator. In this study, the design of an actuator structured based on origami is presented, and analyses on benefits in moment amplification and power amplification from the OSCA design and air compressibility are examined. These efforts provide an insight into producing high power by the OSCA in unison with a low driving-point impedance. [ABSTRACT FROM AUTHOR]

A piezoelectric actuator based on parasitic motion principle is proposed and tested. The piezoelectric actuator is explored to simultaneously realize coarse (long stroke) and fine (high accuracy) motions using dual-servo control method. The working principle of the proposed piezoelectric actuator is discussed, and finite-element method is adopted. A dynamic model of parasitic motion based on the LuGre friction model is simulated using matlab /Simulink. A prototype is manufactured to investigate working performance. Experimental results indicate that the maximum speed of the presented parasitic-type piezoelectric actuator is 7.95 mm/s and the resolution is 10 nm. These findings confirm the feasibility of the dual-servo nanopositioning system using piezoelectric stacks and flexure hinges. [ABSTRACT FROM PUBLISHER]

Pneumatic devices require tight tolerances to keep them leak-free. Specialized companies offer various off-the-shelf devices, while these work well for many applications, there are also situations where custom design and production of pneumatic parts are desired. Cost efficiency, design flexibility, rapid prototyping, and MRI compatibility requirements are reasons why we investigated a method to design and produce different pneumatic devices using a laser cutter from acrylic, acetal, and rubber-like materials. The properties of the developed valves, pneumatic cylinders, and stepper motors were investigated. At 4-bar working pressure, the 4/3-way valves are capable of 5-Hz switching frequency and provide at most 22-L/min airflow. The pneumatic cylinder delivers 48 N of force, the acrylic stepper motor 30 N. The maximum switching frequency over 6-m long transmission lines is 4.5 Hz, using 2-mm tubing. A MRI-compatible robotic biopsy system driven by the pneumatic stepper motors is also demonstrated. We have shown that it is possible to construct pneumatic devices using laser-cutting techniques. This way, plastic MRI-compatible cylinders, stepper motors, and valves can be developed. Provided that a laser-cutting machine is available, the described pneumatic devices can be fabricated within hours at relatively low cost, making it suitable for rapid prototyping applications. [ABSTRACT FROM PUBLISHER]

Robot manufacturing is currently highly specialized, time consuming, and expensive, limiting accessibility and customization. Existing rapid prototyping techniques (e.g., 3-D printing) can achieve complex geometries and are becoming increasingly accessible; however, they are limited to one or two materials and cannot seamlessly integrate active components. We propose an alternative approach called printable robots that takes advantage of available planar fabrication methods to create integrated electromechanical laminates that are subsequently folded into functional 3-D machines employing origami-inspired techniques. We designed, fabricated, and tested prototype origami robots to address the canonical robotics challenges of mobility and manipulation, and subsequently combined these designs to generate a new, multifunctional machine. The speed of the design and manufacturing process as well as the ease of composing designs create a new paradigm in robotic development, which has the promise to democratize access to customized robots for industrial, home, and educational use. [ABSTRACT FROM PUBLISHER]

We report on an actuator based on dielectric elastomers that is capable of antagonistic actuation and passive folding. This actuator enables foldability in robots with simple structures. Unlike other antagonistic dielectric elastomer devices, our concept uses elastic hinges to allow the folding of the structure, which also provides an additional design parameter. To validate the actuator concept through a specific application test, a foldable elevon actuator with outline size of 70 mm \bm \times 130 mm is developed with angular displacement range and torque specifications matched to a 400-mm wingspan micro-air vehicle (MAV) of mass 130 g. A closed-form analytical model of the actuator is constructed, which was used to guide the actuator design. The actuator consists of 125-\mum-thick silicone membranes as the dielectric elastomers, 0.2-mm-thick fiberglass plate as the frame structure, and 50- \mum-thick polyimide as the elastic hinge. We measured voltage-controllable angular displacement up to \pm 26^\circ and torque of 2720 mN \cdot mm at 5 kV, with good agreement between the model and the measured data. Two elevon actuators are integrated into the MAV, which was successfully flown, with the foldable actuators providing stable and well-controlled flight. The controllability was quantitatively evaluated by calculating the correlation between the control signal and the MAV motion, with a correlation in roll axis of over 0.7 measured during the flights, illustrating the high performance of this foldable actuator. [ABSTRACT FROM PUBLISHER]

Nonlinear friction is a dominant factor of the complexity growth of feed drive dynamic behavior. In particular, a feed drive system equipped with rolling contact components such as ball screws and linear motion (LM) guides undergoes impalpable friction behavior. Therefore, proper modeling and compensation of friction in feed drive components play a crucial role in improving the precision of a feed drive system. In this study, to overcome the accuracy limitation of the simplified feed drive model, a distributed component friction model (DCFM) of a feed drive system is developed. Friction has been modeled as a single element of entire feed drive system in the conventional model. However, the proposed DCFM is composed of models of individual feed drive components such as ball screw and LM guide including their friction behaviors. To take advantage of the DCFM by considering both presliding and sliding friction behaviors of each component, LuGre model is applied. For experimental verification of the accuracy of the proposed DCFM, a specially designed feed drive testbed is constructed. Using the testbed, the friction forces of ball screws and LM guides are measured independently. Using the DCFM, a friction observer is built for real-time monitoring and compensation of the friction force. A proportional-derivative feed drive position controller with an observer-based friction compensator is implemented and the experimental results are presented. [ABSTRACT FROM PUBLISHER]

Ball screw drives are used in automation applications and machine tools to translate rotational motion of an electric motor into translational motion of a slide. Their frequency responses show characteristic torsional and translational resonances. The resonance frequencies vary with the slide position, which is due to the distributed stiffness and inertia of the flexible ball screw. The proposed model treats the ball screw as a flexible element, using Ritz series expansions to obtain a finite approximation of the continuous deformations. The use of problem-specific basis functions allows for a low-order approximation, making the model especially well suited for control design. The model shows excellent validation results and reproduces the variation of the resonance frequencies with high accuracy. [ABSTRACT FROM PUBLISHER]

This letter proposes a parallel design for a piezoelectric two-degree-of-freedom nanostepping motor, which performs translation or rotation while its two piezoelectric elements are driven in-phase or out-of-phase electrically. Compared to serial mechanism, parallel designs are more compact, stiffer, and have better dynamical characteristics. Experimental results show that this device works stably. The stepping resolution/stroke values of translation and rotation are 100 nm/6 mm and 0.04°/infinite, respectively. [ABSTRACT FROM PUBLISHER]