Single port access surgery (SPAS) presents surgeons with added challenges that require new surgical tools and surgical assistance systems with unique capabilities. To address these challenges, we designed and constructed a new insertable robotic end-effectors platform (IREP) for SPAS. The IREP can be inserted through a Ø15 mm trocar into the abdomen and it uses 21 actuated joints for controlling two dexterous arms and a stereo-vision module. Each dexterous arm has a hybrid mechanical architecture comprised of a two-segment continuum robot, a parallelogram mechanism for improved dual-arm triangulation, and a distal wrist for improved dexterity during suturing. The IREP is unique because of the combination of continuum arms with active and passive segments with rigid parallel kinematics mechanisms. This paper presents the clinical motivation, design considerations, kinematics, statics, and mechanical design of the IREP. The kinematics of coordination between the parallelogram mechanisms and the continuum arms is presented using the pseudo-rigid-body model of the beam representing the passive segment of each snake arm. Kinematic and static simulations and preliminary experiment results are presented in support of our design choices.
This paper reports the design, development, and magnetic resonance imaging (MRI) compatibility evaluation of an actuated transrectal prostate robot for MRI-guided needle intervention in the prostate. The robot performs actuated needle MRI-guidance with the goals of providing (i) MRI compatibility, (ii) MRI-guided needle placement with accuracy sufficient for targeting clinically significant prostate cancer foci, (iii) reducing interventional procedure times (thus increasing patient comfort and reducing opportunity for needle targeting error due to patient motion), (iv) enabling real-time MRI monitoring of interventional procedures, and (v) reducing the opportunities for error that arise in manually actuated needle placement. The design of the robot, employing piezo-ceramic-motor actuated needle guide positioning and manual needle insertion, is reported. Results of a MRI compatibility study show no reduction of MRI signal-to-noise-ratio (SNR) with the motors disabled. Enabling the motors reduces the SNR by 80% without RF shielding, but SNR is only reduced by 40% to 60% with RF shielding. The addition of radio-frequency shielding is shown to significantly reduce image SNR degradation caused by the presence of the robotic device. An accuracy study of MRI-guided biopsy needle placements in a prostate phantom is reported. The study shows an average in-plane targeting error of 2.4 mm with a maximum error of 3.7 mm. These data indicate the system's needle targeting accuracy is similar to that obtained with a previously reported manually actuated system, and is sufficient to reliably sample clinically significant prostate cancer foci under MRI-guidance.
This paper presents the design and control of an MRI-compatible 1-DOF needle driver robot and its precise position control using pneumatic actuation with long transmission lines. MRI provides superior image quality compared to other imaging modalities such as CT or ultrasound, but imposes severe limitations on the material and actuator choice (to prevent image distortion) due to its strong magnetic field. We are primarily interested in developing a pneumatically actuated breast biopsy robot with a large force bandwidth and precise targeting capability during radio-frequency ablation (RFA) of breast tumor, and exploring the possibility of using long pneumatic transmission lines from outside the MRI room to the device in the magnet to prevent any image distortion whatsoever. This paper presents a model of the entire pneumatic system. The pneumatic lines are approximated by a first order system with time delay, because its dynamics are governed by the telegraph equation with varying coefficients and boundary conditions, which cannot be solved precisely. The slow response of long pneumatic lines and valve subsystems make position control challenging. This is further compounded by the presence of non-uniform friction in the device. Sliding mode control (SMC) was adopted, where friction was treated as an uncertainty term to drive the system onto the sliding surface. Three different controllers were designed, developed, and evaluated to achieve precise position control of the RFA probe. Experimental results revealed that all SMCs gave satisfactory performance with long transmission lines. We also performed several experiments with a 3-DOF fiber-optic force sensor attached to the needle driver to evaluate the performance of the device in the MRI under continuous imaging.
This paper presents a self-contained powered knee and ankle prosthesis, intended to enhance the mobility of transfemoral amputees. A finite-state based impedance control approach, previously developed by the authors, is used for the control of the prosthesis during walking and standing. Experiments on an amputee subject for level treadmill and overground walking are described. Knee and ankle joint angle, torque, and power data taken during walking experiments at various speeds demonstrate the ability of the prosthesis to provide a functional gait that is representative of normal gait biomechanics. Measurements from the battery during level overground walking indicate that the self-contained device can provide more than 4500 strides, or 9 km, of walking at a speed of 5.1 km/h between battery charges.
In 1991, a novel robot named MIT-MANUS was introduced as a test bed to study the potential of using robots to assist in and quantify the neurorehabilitation of motor function. It introduced a new modality of therapy, offering a highly backdrivable experience with a soft and stable feel for the user. MIT-MANUS proved an excellent fit for shoulder and elbow rehabilitation in stroke patients, showing a reduction of impairment in clinical trials with well over 300 stroke patients. The greatest impairment reduction was observed in the group of muscles exercised. This suggests a need for additional robots to rehabilitate other target areas of the body. Previous work has expanded the planar MIT-MANUS to include an antigravity robot for shoulder and elbow, and a wrist robot. In this paper we present the "missing link": a hand robot. It consists of a single-degree-of-freedom (DOF) mechanism in a novel statorless configuration, which enables rehabilitation of grasping. The system uses the kinematic configuration of a double crank and slider where the members are linked to stator and rotor; a free base motor, i.e., a motor having two rotors that are free to rotate instead of a fixed stator and a single rotatable rotor (dual-rotor statorless motor). A cylindrical structure, made of six panels and driven by the relative rotation of the rotors, is able to increase its radius linearly, moving or guiding the hand of the patients during grasping. This module completes our development of robots for the upper extremity, yielding for the first time a whole-arm rehabilitation experience. In this paper, we will discuss in detail the design and characterization of the device.
This paper presents the design and actuation of a six-degree-of-freedom (6-DOF) manipulator for a handheld instrument, known as "Micron," which performs active tremor compensation during microsurgery. The design incorporates a Gough-Stewart platform based on piezoelectric linear motor, with a specified minimum workspace of a cylinder 4 mm long and 4 mm in diameter at the end-effector. Given the stall force of the motors and the loading typically encountered in vitreoretinal microsurgery, the dimensions of the manipulator are optimized to tolerate a transverse load of 0.2 N on a remote center of motion near the midpoint of the tool shaft. The optimization yields a base diameter of 23 mm and a height of 37 mm. The fully handheld instrument includes a custom-built optical tracking system for control feedback, and an ergonomic housing to serve as a handle. The manipulation performance was investigated in both clamped and handheld conditions. In positioning experiments with varying side loads, the manipulator tolerates side load up to 0.25 N while tracking a sinusoidal target trajectory with less than 20 μm error. Physiological hand tremor is reduced by about 90% in a pointing task, and error less than 25 μm is achieved in handheld circle-tracing.
Magnetic resonance imaging (MRI) can provide high-quality 3-D visualization of prostate and surrounding tissue, thus granting potential to be a superior medical imaging modality for guiding and monitoring prostatic interventions. However, the benefits cannot be readily harnessed for interventional procedures due to difficulties that surround the use of high-field (1.5T or greater) MRI. The inability to use conventional mechatronics and the confined physical space makes it extremely challenging to access the patient. We have designed a robotic assistant system that overcomes these difficulties and promises safe and reliable intraprostatic needle placement inside closed high-field MRI scanners. MRI compatibility of the robot has been evaluated under 3T MRI using standard prostate imaging sequences and average SNR loss is limited to 5%. Needle alignment accuracy of the robot under servo pneumatic control is better than 0.94 mm rms per axis. The complete system workflow has been evaluated in phantom studies with accurate visualization and targeting of five out of five 1 cm targets. The paper explains the robot mechanism and controller design, the system integration, and presents results of preliminary evaluation of the system.
This paper presents the design of an adaptive observer that is implemented to enable real-time dynamic force sensing and parameter estimation in an optically trapped probing system. According to the principle of separation of estimation and control, the design of this observer is independent of that of the feedback controller when operating within the linear range of the optical trap. Dynamic force sensing, probe steering/clamping, and Brownian motion control can, therefore, be developed separately and activated simultaneously. The adaptive observer utilizes the measured motion of the trapped probe and input control effort to recursively estimate the probe-sample interaction force in real time, along with the estimation of the probing system's trapping bandwidth. This capability is very important to achieving accurate dynamic force sensing in a time-varying process, wherein the trapping dynamics is nonstationary due to local variations of the surrounding medium. The adaptive estimator utilizes the Kalman filter algorithm to compute the time-varying gain in real time and minimize the estimation error for force probing. A series of experiments are conducted to validate the design of and assess the performance of the adaptive observer.
Robotic motion planning algorithms used for task automation in robotic surgical systems rely on availability of accurate models of target soft tissue's deformation. Relying on generic tissue parameters in constructing the tissue deformation models is problematic because, biological tissues are known to have very large (inter- and intra-subject) variability. A priori mechanical characterization (e.g., uniaxial bench test) of the target tissues before a surgical procedure is also not usually practical. In this paper, a method for estimating mechanical parameters of soft tissue from sensory data collected during robotic surgical manipulation is presented. The method uses force data collected from a multiaxial force sensor mounted on the robotic manipulator, and tissue deformation data collected from a stereo camera system. The tissue parameters are then estimated using an inverse finite element method. The effects of measurement and modeling uncertainties on the proposed method are analyzed in simulation. The results of experimental evaluation of the method are also presented.
Force sensors provide critical information for robot manipulators, manufacturing processes, and haptic interfaces. Commercial force sensors, however, are generally not adapted to specific system requirements, resulting in sensors with excess size, cost, and fragility. To overcome these issues, 3D printers can be used to create components for the quick and inexpensive development of force sensors. Limitations of this rapid prototyping technology, however, require specialized design principles. In this paper, we discuss techniques for rapidly developing simple force sensors, including selecting and attaching metal flexures, using inexpensive and simple displacement transducers, and 3D printing features to aid in assembly. These design methods are illustrated through the design and fabrication of a miniature force sensor for the tip of a robotic catheter system. The resulting force sensor prototype can measure forces with an accuracy of as low as 2% of the 10 N measurement range.
This paper presents a new type of pneumatic motor, a pneumatic step motor (PneuStep). Directional rotary motion of discrete displacement is achieved by sequentially pressurizing the three ports of the motor. Pulsed pressure waves are generated by a remote pneumatic distributor. The motor assembly includes a motor, gearhead, and incremental position encoder in a compact, central bore construction. A special electronic driver is used to control the new motor with electric stepper indexers and standard motion control cards. The motor accepts open-loop step operation as well as closed-loop control with position feedback from the enclosed sensor. A special control feature is implemented to adapt classic control algorithms to the new motor, and is experimentally validated. The speed performance of the motor degrades with the length of the pneumatic hoses between the distributor and motor. Experimental results are presented to reveal this behavior and set the expectation level. Nevertheless, the stepper achieves easily controllable precise motion unlike other pneumatic motors. The motor was designed to be compatible with magnetic resonance medical imaging equipment, for actuating an image-guided intervention robot, for medical applications. For this reason, the motors were entirely made of nonmagnetic and dielectric materials such as plastics, ceramics, and rubbers. Encoding was performed with fiber optics, so that the motors are electricity free, exclusively using pressure and light. PneuStep is readily applicable to other pneumatic or hydraulic precision-motion applications.
The use of electrostatic forces in micromechanical systems is well
known, but quite high voltages are needed to produce usable forces. In
this perspective paper, a 1.5-V battery-supplied integrated circuit able
to drive an electrostatic micromotor is presented. The
application-specific integrated circuit (ASIC) can output signals up to
80 V, with low-voltage controlling signals. It is especially designed
for portable (wristwatch-like) applications. High voltage can be
produced by either switching or charge-pumping power supplies
An automated biomechatronic submicroliter fluid handling system
for processing deoxyribonucleic acid (DNA) has been developed in the
Genomation Laboratory, Department of Electrical Engineering, University
of Washington, Seattle. This first generation system, ACAPELLA-1K, can
process 1000 samples in 8 h in preparation for DNA sequencing using
sample volumes ten times smaller than current state-of-the art manual
and automated instrumentation. The system is based upon a
proof-of-concept system that was developed by the Genomation Laboratory.
The ACAPELLA-1K is the first integration of modules for fluid
aspiration, dispensing, mixing, transport, and thermal processing that
have been designed and developed with corporate partners Orca Photonic
Systems, Inc., Redmond, WA, and Engineering Arts, Mercer Island, WA.
These modules, comprising piezoceramic actuators, pneumatic pumps,
linear mechanisms, thermal controllers, optical sensors, electronics,
computer control, and software, are described in detail. Processing
statistics are presented and successful experimental results are
In plants in many industries, there exist a lot of transfer systems with vibration mechanisms. While transfer without residual vibration is usually demanded in these plants, this requirement necessitates large numbers of sensors and complicated models for control design. Therefore, This work presents a trajectory control design method to suppress residual vibration in transfer systems without the need to directly measure vibration. The proposed method consists of two parts. First, the frequency characteristics of the controller, comprised of control elements with simple structures such as a notch filter and a low-pass filter, are shaped as needed to suppress vibration. Next, various parameters of the control elements are determined by solving an optimization problem with penalty terms expressed by the constraints of both the time and frequency domains. The proposed method is applied to a liquid container transfer system, with special consideration given to the suppression of sloshing (liquid vibration) as well as to the maintenance of a high-speed transfer on the container's three-dimensional transfer path. The obtained controller demonstrates good performance for all demands. The effectiveness of the control design method is shown by experiments.
This paper presents a versatile atomic-force-microscope (AFM)-based two-axis probing system for 2.5-D nanometrology. Central to this system is a two-axis compliant micromanipulator based on the AFM probe whose orientation and position can be actively changed in the scanning plane. Three enabling technologies are proposed to uniformly scan the section of the sample surface within this plane. First, an orientation control system is developed that controls the tip-orientation to track the changes in normal of the surface section. Second, tapping mode-based tip-sample interaction scheme is developed wherein the direction of tip oscillation and the peak force are controlled, according to the local orientation of the section. Third, a two-axis scanning scheme is developed wherein the scanning and interaction control axes are aligned along the tangent and normal to the local section. Taken together, these technologies enable the entire scanning process to conform to the geometry of the sample in the scanning plane and facilitate metrology of samples with large geometric variation along the two axes. In this paper, the developed probing system is used to scan the entire top surface of a micropipette and demonstrate greater access and absence of artifacts when compared to a conventional scan.
Compared to traditional tendon-driven robots, the mechanism design of the National Taiwan University hand has an uncoupled configuration and is compact in size. In this paper, a specially designed compact control system, which is embedded into the NTU hand to satisfy the limited space, is developed to perform the control of the five-finger robot with 17 degrees of freedom (DOF). There are total 17 actuators including transmission mechanism, 17 potentiometers, and 18 tactile sensor pads to be integrated. Those 17 actuators should be controlled simultaneously by integrating 17 position sensing signals and 18 tactile signals. Multi-loop position control is further complicated by multi-loop force control as well as sensor integration. The proposed control system distributes the computation load into several modules and utilizes the DSP chip. It takes advantage of the fuzzy control by introducing the knowledge of human and sensor fusion with the finger joint and tactility. Using the communication function of the control system, the knowledge bases can be loaded for high level computation and modified during run time.
The purpose of this paper is to present our results in developing a dynamic model of the Mitsubishi PA-10 robot arm for the purpose of low-velocity trajectory tracking using low-feedback gains. The PA-10 is ideal for precise manipulation tasks because of the backdrivability, precise positioning capabilities, and zero backlash afforded by its harmonic drive transmission (HDT). However, the compliance and oscillations inherent in harmonic drive systems, and the lack of any technical information on the internal dynamics of the transmission, make the development of an accurate dynamic model of the robot extremely challenging. The novelty of this research is therefore the development of a systematic algorithm to extract the model parameters of a harmonic drive transmission in the robot arm to facilitate model-based control. We have modeled all seven joints of the Mitsubishi PA-10, and we have done several experiments to identify the various parameters of the harmonic drive system. We conclude with a sample trajectory-tracking task that demonstrates our model-based controller for the Mitsubishi PA-10 robot arm.
Electrokinetics is the study of the motion of bulk fluids or selected particles embedded in fluids when they are subjected to electric fields. With the recent developments in microfabrication, electrokinetics provides effective manipulation techniques in the micro and nano domains, which matches the length scale of various biological objects. The ability to manipulate objects down to molecular levels opens new avenues to exploit biological science and technology. Understanding of the fundamental characteristics and limitations of the forces becomes a crucial issue for successful applications of these force fields. In this paper, we review and examine the range of influence for electrokinetically manipulated biological objects in microdevices, which can lead to interesting applications in biotechnology.
An adaptive visual feedback scheme is designed to perform 3D
positioning tasks. The dynamic camera-object interaction model is
derived in discrete time, since the visual sampling time is not
negligible at the current state of technology. Active contours are used
to track the 2D projection of the visible object's surface in the image
plane. Uniform asymptotic stability of the image reference set-point is
proved using the Lyapunov direct method, and a 3D estimation procedure,
based on prediction errors, is used to cope with the unknown depth of
the object. Experimental results with a 6-DOF robot manipulator in
eye-in-hand configuration validate the theoretical framework in real
Feedback linearization is a promising approach to the nonlinear control problem posed by active magnetic bearing systems. In this paper, feedback linearization is employed in combination with robust control techniques for the regulation of a single axis test rig actuated by a multiple pole magnetic bearing. To this end, a nonlinear polynomial model of the magnetic actuator was developed based on its experimental calibration. The effect of the amplifier and measurement system dynamics on the feedback linearization performance, was also examined, and compensation filters were developed. Finally, an uncertainty framework was proposed for the linearized plant, and a robust controller was designed via μ synthesis. Experimental results demonstrate that the feedback-linearized active magnetic bearing system can achieve stability and the specified performance over the entire range of bearing clearance. The introduction of compensation filters is shown to be essential to this result.
This paper develops a Markovian jump model to describe the fault occurrences in a manipulator robot of three joints. This model includes the changes of operation points and the probability that a fault occurs in an actuator. After a fault, the robot works as a manipulator with free joints. Based on the developed model, a comparative study among three Markovian controllers, H<sub>2</sub>, H<sub>infin</sub>, and mixed H<sub>2</sub>/H<sub>infin</sub> is presented, applied in an actual manipulator robot subject to one and two consecutive faults.
Overlapping radiofrequency ablation (RFA) in large tumor treatment requires multiple insertions of electrodes, which often compromise its efficacy and predictability. Surgical robot is a promising candidate for the execution of multiple RFA in large tumor treatment in terms of accuracy and speed. In this paper, we share our experience of design and implementation of a novel robotic system specialized for overlapping RFA. It consists of two components: a robotic manipulator and an automatic ablation planning module. The manipulator architecture is designed to facilitate the kinematic requirement for the multiple overlapping ablation technique within the constraints of minimally invasive surgery. An efficient “Voxel Growing” algorithm is adopted to automatically produce the ablation points according to the tumor's profile. The feasibility of the proposed robotic system is demonstrated by extensive simulation- and experiment-based evaluation conducted on ex vivo porcine liver.
We have developed a standing style transfer system, or "ABLE," for a person with disabled legs. It allows travel in a standing posture even on uneven ground, a standing up motion from a chair, and allows the stairs. ABLE consists of three modules: a pair of telescopic crutches, a powered lower extremity orthosis, and a pair of mobile platforms. We present here the conceptual design of ABLE and the motion of each module. Cooperative operations using the three modules are discussed through simulations. The standing up motion from a chair and ascending the stairs, however, have problems with adaptability to the environment and safety, because it executes the movement that has till now relied on telescopic crutches. To solve these problems, we propose a new motion technique and compare it with the previous one. In this paper, some experimental results are also presented
The delayed resonator (DR) is an active vibration control approach
where a passive mass-spring-damper arrangement is converted into an
undamped real-time tunable dynamic absorber using partial state feedback
with time delay. In the presented work, robustness of the control
strategy against fluctuations in the structural parameters of the
controlled system is addressed. A single-step automatic tuning algorithm
based on online parameter identification is developed as a means of
increasing robustness against uncertainties and variations in the
mechanical properties of the absorber arrangement. The tuning process is
completed within the absorber section of the controlled system with no
external information from the primary structure. Implementation of the
algorithm is illustrated by a numerical example, and demonstrated
experimentally on a clamped-clamped flexible beam
In this paper, a new Kalman filtering technique, unscented Kalman filter (UKF), is utilized both experimentally and theoretically as a state estimation tool in field-oriented control (FOC) of sensorless ac drives. Using the advantages of this recent derivative-free nonlinear estimation tool, rotor speed and dq-axis fluxes of an induction motor are estimated only with the sensed stator currents and voltages information. In order to compare the estimation performances of the extended Kalman filter (EKF) and UKF explicitly, both observers are designed for the same motor model and run with the same covariance matrices under the same conditions. In the simulation results, it is shown that UKF, whose several intrinsic properties suggest its use over EKF in highly nonlinear systems, has more satisfactory rotor speed and flux estimates, which are the most critical states for FOC. These simulation results are supported with experimental results
This paper addresses the problem of torque and velocity ripple elimination in AC permanent magnet (PM) motor control systems. The torque ripples caused by DC offsets that are present in the current sensors of the motor driver and the digital-to-analog converters of the motion controller are studied and formulated mathematically. These torque ripples eventually generate velocity ripples at the speed output and degrade the system performance. In this paper the torque ripples are modeled as a sinusoidal function with a frequency depending on the motor speed. The internal model principle (IMP) is then used to design a controller to eliminate the torque and velocity ripples without estimating the amplitude and the phase values of the sinusoidal disturbance. A gain scheduled (GS) robust two degree of freedom (2DOF) speed regulator based on the IMP and the pole-zero placement is developed to eliminate the torque and velocity ripples and achieve a desirable tracking response. Simulation and experimental results reveal that the proposed GS robust 2DOF speed regulator can effectively eliminate the torque ripples generated by DC current offsets, and produce a velocity ripple-free output response.
Measuring the trajectory of a rigid body in space is commonly done using an inertial measurement unit composed of one triaxial accelerometer and one triaxial gyroscope. When the rigid body undergoes high accelerations, it is often preferable to resort to an array of accelerometers rather than the traditional accelerometer-gyroscope combination, an approach that is now common in crashworthiness and other biomechanics applications. In this paper, we present an algorithm for the estimation of the rigid-body angular velocity from the centripetal components of the accelerations measured by the array of accelerometers. The proposed algorithm and the others available in the literature were benchmarked using the accelerometer array octahedral constellation of twelve accelerometers. In the reported testing conditions, the proposed method is slightly more robust than any other based on centripetal-acceleration measurements.
Acceleration computation based on simple numerical differentiation
from an optical encoder signal may be very erroneous, especially in the
low-velocity and low-acceleration regions. To overcome this problem, a
novel approach to estimating acceleration in these regions is proposed
in this paper. This low-acceleration estimator, which is a computer
algorithm, is based on the fact that the displacement signal from the
encoder is accurate. Since the bandwidth of this estimator is rather
limited, it can be used in combination with the traditional numerical
differentiation approach in order to cover a wide velocity range. It was
shown in various simulations and experiments that this combined
acceleration estimator can yield accurate acceleration estimates over a
wide range of velocities. Furthermore, when this estimator is applied to
a friction compensation system, the effect of low-velocity friction can
be reduced significantly by its capability to detect small changes in
acceleration caused by friction
The human hand is very sensitive to the high-frequency accelerations produced by tool contact with a hard object, yet most time delayed telerobots neglect this feedback band entirely in order to achieve stability. We present a control architecture that both incorporates this important information and provides the ability to scale and shape it independently of the low-frequency force feedback. Leveraging the clean power flows afforded by wave variables, this augmented controller preserves the passivity of any environment that it renders to the user, but is not subject to the limitations of being passive itself. This architecture guarantees stability in the presence of communication delay while achieving a level of feedback not possible with a passive controller. We show experimentally that this feedback augmentation and shaping can present a high-frequency acceleration profile to the user's hand that is similar to that experienced by the slave end effector. Two simple user studies also show that the feedback augmentation improves the user's perception, performance, and confidence with the given tasks. We anticipate that these natural haptic cues will make teleoperative systems easier to use and thus more widely applicable.
Joint acceleration and velocity feedbacks are incorporated into a
classical internal force control of a robot in contact with the
environment. This is intended to achieve a robust contact transition and
force tracking performance for varying unknown environments, without any
need of adjusting the controller parameters. A unified control structure
is proposed for free motion, contact transition, and constrained motion
in view of the consumption of the initial kinetic energy generated by a
nonzero impact velocity. The influence of the velocity and acceleration
feedbacks, which are introduced especially for suppressing the
transition oscillation, on the postcontact tracking performance is
discussed. Extensive experiments are conducted on the third joint of a
three-link direct-drive robot to verify the proposed scheme for
environments of various stiffnesses, including elastic (sponge), less
elastic (cardboard), and hard (steel plate) surfaces. Results are
compared with those obtained by the transition control scheme without
the acceleration feedback. The ability of the proposed control scheme in
resisting the force disturbance during the postcontact period is also
Concerns control of an electrodynamic shaker for vibration-proof
testing of electronic products. An acceleration controller for such a
shaker fed by a switching-mode power amplifier is presented in this
paper. First, the dynamic model of the shaker system is found and a
high-performance current-controlled pulsewidth modulated inverter is
designed and implemented. Then, a sophisticated acceleration control
scheme being capable of waveform and magnitude regulation controls is
proposed to lessen the undesired harmonic vibration caused by
switching-mode driven power. In acceleration waveform control, the
feedback controller is augmented with a feedforward controller and
robust controller for obtaining excellent waveform tracking performance
over a wide frequency range. As to the magnitude regulation control, the
amplitude of the sinusoidal acceleration is accurately controlled to be
equal to the setting value. Theoretical basis, practical consideration,
and implementation of the proposed controllers are described in detail.
Good current and acceleration control characteristics of the designed
shaker are demonstrated by some measured results
This paper considers a pivot friction compensator using the
combination of an accelerometer and a disturbance observer. Noting that
the pivot torque bias due to uncertain disturbances and nonlinearities
such as pivot friction is approximately the difference between the
scaled voice-coil motor (VCM) current and the scaled carriage angular
acceleration, a disturbance observer to estimate the bias can be
constructed using the above two continuously measured signals. By
feeding back the bias estimate into the VCM amplifier, the frequency
response from the VCM current to the carriage angular acceleration is
linearized to be a constant gain within the observer bandwidth. The
proposed cancellation scheme provides wider bandwidth bias rejection and
better settling performance than traditional bias compensation schemes.
Experiments have confirmed that the cancellation scheme is effective in
the frequency range 0-700 Hz
This paper discusses the design, calibration, simulation, and experimental validation of a kinematically redundant inertial measurement unit that is based solely on accelerometers. The sensor unit comprises 12 accelerometers, two on each face of a cube. The location and direction of the sensors are determined so as to locally optimize the numerical conditioning of the system of governing kinematic equations. The orientational installation error of each sensor is identified by off-line iterative processing of the gravitational acceleration measurements made at a number of known orientations of the unit, thus allowing subsequent calibration. Furthermore, a novel procedure is developed through which the acceleration measurements can be used to directly determine the body angular velocity; this results in a major accuracy improvement over similar works whereby the angular velocity is obtained via integrating the angular acceleration. Experimental results are presented to validate the methodology, design, and implementation.
The behavior of a new planar piezoelectric accelerometer is
investigated, both theoretically and experimentally. The proposed
accelerometer is composed of a piezoceramic ring filled, in its inner
space, with a seismic mass. The theoretical analysis has been carried
out by using a matrix model of the radial symmetric modes of the thin
piezoceramic ring, proposed by the authors (1996). The numerical results
obtained for the empty ring show that, with the response being constant,
the bandwidth increases when the annulus radius increases. On the
contrary, by inserting a high-density and stiffness seismic mass, both
the response and the bandwidth increase by increasing the percent
quantity of the seismic mass. The measurements of admittance and
sensitivity, carried out on a test specimen, validate the computed
results and demonstrate that the accelerometer is planar. Finally, an
accelerometer composed of two of such elements, stacked and connected in
parallel, has been realized
A smart structure technology for autonomous gain and phase tailoring was adapted to develop a new accelerometer that possesses both an excellent low-frequency response and a high operational bandwidth. The freedom associated with the uncoupling of the gain and phase tailoring to an accelerometer-based structure transfer function can be shown to vastly expand the performance area of traditional accelerometers. We used free-fall detection to demonstrate this newly found capability with its wide applicability to portable devices and which is perceived as extremely difficult to pursue for magnetic disk drives. A micromachined accelerometer was developed to demonstrate the expanded applicability of this innovative concept that integrates smart structure technology to accelerometer design. Both theoretical derivations and experimental verification of this new class of accelerometers are detailed in this paper.
A prototype design of an inexpensive polymer-based tunneling accelerometer is described in this paper. Instead of silicon, polymethyl methacrylate (PMMA) is used as the mechanical material. By using silicon molds fabricated by conventional lithography and wet-etching techniques in hot embossing, PMMA structures can be replicated within 20 min. The performance of the tunneling sensor can be estimated and improved based on mechanical-level analysis by ANSYS and system-level analysis by MATLAB. The nonlinear tunneling mechanism and electrostatic actuation are linearized using small-signal approximation. To enhance the stability and broaden the bandwidth of the tunneling accelerometer system, a feedback control system with one zero and two poles is designed. The dynamic range of the system is greatly enhanced. The bandwidth of the closed-loop system is approximately 15 kHz.
This paper proposes a new robotic manipulator using stack able 4-BAR mechanisms for single port access (SPA) surgery where the operation is performed by inserting multiple manipulators through one small body cavity. The proposed manipulator has the advantage that all actuators are able to be separated from the driving mechanism. In other words, it is possible to separate the electrical actuators from the mechanical linkage/joint components in the manipulators. Thus, the robotic manipulators, including the working joints and linkages, can be fabricated using selective materials that are light-weight and slim so that the multiple manipulators can be inserted through one small cavity. Moreover, since the suggested manipulator makes use of an individual 4-BAR mechanism to drive each independent joint, it is structurally strong. Using the kinematic model, we conduct a kinematic synthesis (design methodology) because the operating range of each working joint is usually limited by the design parameters of 4-BAR. Finally, we show that the stackable 4-BAR manipulator is a good alternative for SPA surgery through numerical simulations and implementation of the proposed manipulator.
A multisensor approach that capitalizes on the existing magnetic fields in permanent-magnet-based actuators to achieve unobtrusive high-accuracy position sensing is presented. As magnetic-field models are position dependent, their inverse problems are often highly nonlinear with nonunique solution. This paper illustrates the principle and motivation for a multisensor approach using the concepts of parametric spaces to take advantage of multiple independent sensor measurements to induce a unique field-position correspondence in multisource fields. A direct mapping approach using supervised back-propagation artificial neural networks is utilized to attain positional information from distributed field measurements. Using an experimental rotary setup containing 24 magnetic sources, the measurements obtained from a network of magnetic Hall-effect sensors are statistically characterized and used to investigate the factors affecting the accuracy of the sensing system. Of particular interest are the combined effects of the number and spatial configuration of the sensors. Two types of sensor arrangement are investigated: an in-phase configuration consisting of evenly spaced sensors and a staggered configuration where unevenly spaced sensors concurrently measure different points of a periodic field. Using a network of 24 single-axis Hall-effect sensors in staggered configuration, the system is capable of achieving nanodegree angular positional accuracy.
Built-in torque sensing for Harmonic Drives is attractive since it
maintains mechanical characteristics of the gear while providing
detection of the transmitted torque. Torque sensing by using strain
gauges has been studied, but is not widely used yet due to a relatively
high signal fluctuation, which is generated by the gear operation.
Characteristics of the signal fluctuation are analyzed in this paper,
and a method to effectively compensate the signal fluctuation is
proposed. The signal fluctuation is perfectly compensated by adjustment
of the strain gauge sensitivities. A minimum number of strain gauges
needed to compensate the signal fluctuation is derived. The experimental
result with three strain gauges compensating the basic frequency
component of the signal fluctuation is shown
Reports on the design, fabrication, and testing of an
electrostatic microactuator for a magnetic hard disk drive (HDD)
tracking servo. The design requirements for a microactuator are
investigated. These include high Z-directional stiffness, low in-plane
stiffness, high structural aspect ratio, large output force, high area
efficiency, low cost, and mass batch production. An area-efficient
rotary microactuator design was devised, and microactuators were
successfully fabricated using innovative processing technologies. The
microactuator has a structural thickness of 40 μm with a minimum
gap/structure width of approximately 2 μm. Its frequency response was
measured and it was determined that it can be modeled as a second-order
linear system, up to the 26-kHz frequency range. Moreover, the
microactuator will enable the design of a servo system that exceeds a
5-kHz servo bandwidth, which is adequate to achieve a track density of
more than 25 kilotrack per inch (kTPI). The microactuator/slider
assembly was also tested on a spinning disk, with its position
controlled by a PID controller using the magnetic position error signal
written on the disk. An accuracy of about 0.05 μm was observed when
the servo controller was turned on. Continuous-time dual-stage servos
were designed and simulated using the μ-synthesis technique. A
sequentially designed SISO and a MIMO control design method have been
shown to be capable of meeting prescribed uncertainty and performance
Image-guided percutaneous interventions are common procedures used for diagnosis or therapeutic purposes. The clinical demand for such interventions is growing since they are minimally invasive. To increase the quality of the operations and provide optimal accuracy and safety to patients, puncture robots may be very helpful. This paper presents a new robotic architecture designed to perform abdominal and thoracic punctures under computer tomography (CT) or MRI guidance. Innovations concerning the robotic architecture, materials, and energy sources are described. Segmentation and registration algorithms have been developed to localize the robot on images coming from CT or MRI devices, and a specific control loop is used to verify the movements and the positioning of the robot. The results of the initial experiments made under CT and MRI environments are presented.
This paper presents a structural design method of robust motion controllers for high-accuracy positioning systems, which makes it possible to tune the performance of the whole closed-loop system systematically. First, a stabilizing control input is designed based on Lyapunov redesign for the system in the presence of uncertainty and disturbance. And adopting the internal model following control, robust internal-loop compensator (RIC) is proposed. By using the structural characteristics of the RIC, disturbance attenuation properties and the performance of the closed-loop system determined by the variation of controller gains are analyzed. Next, in order to design a robust motion controller for a high performance positioning system, dual RIC structure is proposed and it is shown that if the synthesis of the robust motion control law is performed in the RIC framework, the robust property of RIC can be naturally implanted in the feedback controller. The proposed structural design of robust motion controller provides a systematic approach to the problem of robust stability and performance requirement in the face of uncertainty. Furthermore, by allowing the tradeoffs between robust stability and performance to be quantified in a simple fashion, it can illuminate systematic design procedure of the robust motion controllers. Finally, the proposed method is verified through simulation and the performance is evaluated by experiments using a high-accuracy positioning system.
This paper discusses the overall positioning accuracy of a neurosurgical robot system. First, the overall positioning accuracy of the robot system is analyzed and formulated. Then, the efforts are focused on improving the positioning accuracy of the robot arm. A revised Denavit--Hartenberg (D-K) kinematic model is addressed to describe two nearly parallel joint axes for the calibration of the robot. The joint transmitting error of the robot is compensated by using a backpropagation (BP) neural network. Finally, the absolute positioning accuracy of the robot arm is measured. A phantom is designed to simulate the clinical workflow of the robot-assisted neurosurgery for measuring the overall positioning accuracy of the robot system. The results show that the positioning error of the robot arm is less than 1 mm, which is comparable to that of stereotactic frames; and that the overall positioning error of the robot system is caused mainly by target registration error, which proves the effectiveness of our efforts.
It has been reported that, in impedance control, there exists a dilemma between impedance accuracy and robustness against modeling error. As a solution to this dilemma, an accurate and robust impedance control technique is developed based on internal model control structure and time-delay estimation: the former injects desired impedance and corrects modeling error, the latter estimates and compensates the nonlinear dynamics of robot manipulators. Owing to the simple structure, the proposed control is designed without requiring entire model computation or complex algorithms. In 2-DOF SCARA-type robot experiments, the accuracy and robustness of the proposed control are confirmed through comparisons with other competent controllers including impedance control with disturbance observer.
Proportional gains are to be increased in force control processes in order to reduce the force error. However, the control process may become unstable for large gains due to the digital and delay effects. In this paper, the act-and-wait control concept is compared with the traditional, continuous control concept for a digital force control model with proportional feedback subject to a short, one sample unit feedback delay. Both concepts are implemented in an experimental setup. It is shown that the proportional gain can be increased significantly without losing stability when the act-and-wait controller is used; thus, the force error can effectively be decreased this way. The results are confirmed by experiments.
The development of a fast, accurate, and inexpensive
position-controlled pneumatic actuator that may be applied to a variety
of practical positioning applications is described. A novel pulse width
modulation (PWM) valve pulsing algorithm allows on/off solenoid valves
to be used in place of costly servo valves. The open-loop characteristic
is shown both theoretically and experimentally to be near symmetrical. A
comparison of the open- and closed-loop responses of standard PWM
techniques and that of the novel PWM technique shows that there has been
a significant improvement in the control. A linear process model is
obtained from experimental data using system identification. A
proportional integral derivative controller with added friction
compensation and position feedforward has been successfully implemented.
A worst case steady-state accuracy of 0.21 mm was achieved with a rise
time of 180 ms for step inputs from 0.11 to 64 mm. Following errors to
64-mm S-curve profiles were less than 2.0 mm. The controller is robust
to a sixfold increase in the system mass. The actuator's overall
performance is comparable to that achieved by other researchers using
A control law is developed for an inexpensive pneumatic motion control system using four solenoid on/off valves and a position feedback sensor. A sliding-mode approach is used, which is well known for its tolerance for system uncertainties. In contrast to previous control laws, our approach does not use pulsewidth modulation. The control law has an energy-saving mode that saves electrical power, reduces chattering, and prolongs the valve's life. Our simulation and experimental results show that the proposed tracking control law performs very well with good tracking and relatively low steady-state position errors
Real-control applications of any nature can be affected by saturation limits that generate windup. When saturation occurs in a device its performance deteriorates. Electromagnetic actuators for industrial applications are being utilized ever more frequently for positioning and tracking control problems. One of the most important requirements in tracking trajectories is to achieve a soft landing, which guarantees reliable functionality and a longer component life. This paper presents an application of a typical electromagnetic actuator through a hardware-in-the-loop structure in which a soft landing is required in the tracking trajectory. To avoid saturation, which prevents soft landings, a specific new control law is developed. The proposed technique is based on a cyclic adaptive current preaction combined with a sliding surface. The technique consists of building a control law so that the position of the valve at which its velocity assumes its minimum is as close as possible to the landing point. At this time point, the magnetic force compensates for the elastic force and the preaction component is switched off. An experimental setup using a hardware-in-the-loop to allow a pilot investigation, model validation, and testing before implementation is considered. Real measurements of the proposed method are shown.
In this paper, a problem, called the initial formation problem, within the multirobot task allocation domain is addressed. This problem consists in deciding which robot should go to each of the positions of the formation in order to minimize an objective. Two different distributed algorithms that solve this problem are explained. The second algorithm presents a novel approach that uses cost means to model the cost distribution and improves the performance of the task allocation algorithm. Also, we present an approach that integrates distributed task allocation algorithms with a behavior-based architecture to control formations of robot teams. Finally, simulations and real experiments are used to analyze the formation behavior and provide performance metrics associated with implementation in realistic scenarios.