High Bandwidth Force Research Articles

Adaptive Brake Torque Variation Compensation for an Electromechanical Brake

A novel method for attenuation of brake judder directly at the source is proposed, utilizing an electromechanical brake to actively compensate for the variation in brake torque that causes judder. Taking advantage of the high-bandwidth closed-loop clamp force tracking performance offered by an electromechanical brake, an adaptive compensator is designed to estimate the brake torque variation (BTV), and to produce a compensating clamp force command to cancel it. The compensator is tested over fixed and varying BTV frequencies by employing a production-ready prototype EMB. It is demonstrated that significant BTV attenuation is obtained using the proposed approach.

Tapping-mode force spectroscopy using cantilevers with interferometric high-bandwidth force sensors

We quantitatively map the surface forces and elastic modulus in tapping-mode atomic force microscopy (AFM). To achieve this, we use custom-built cantilevers with interferometric high-bandwidth force sensors that can resolve nonlinear tip-sample interaction forces, combined with a set of algorithms to process the force sensor signals in real-time. Our technique achieves quantitative mechanical measurements, while retaining nanoscale spatial resolution and minimal loading forces in tapping-mode AFM. Moreover, conventional tapping-mode AFM images are not affected and can simultaneously be acquired. As a practical demonstration, we use our technique to quantify the mechanical properties of a polystyrene and linear low-density polyethylene blend.

High-Resolution Nanomechanical Mapping Using Interferometric-Force-Sensing AFM Probes

In this paper, we demonstrate high-resolution mapping of composite surfaces based on their nanomechanical properties by employing an atomic force microscope probe that can resolve high-frequency tip-sample interaction forces in tapping-mode atomic force microscopy (AFM) (TM-AFM). Time-resolved force measurements are achieved by a small integrated interferometric high-bandwidth grating force sensor at the end of the cantilever beam. The probes are batch fabricated using optical lithography and are used in an AFM system with no further modification. The fabricated devices are characterized and grating-force-sensor signals and their measured spectra confirm that probes with integrated high-bandwidth force sensors can successfully resolve high-frequency tip-sample interaction forces. We utilize the capability of our probes to form images by recording the amplitude of the higher harmonics of the time-resolved tip-sample interaction forces with lock-in detection. These images show that our probes can successfully map, with high spatial resolution, the mechanical contrast due to different materials and structural differences in composite surfaces.

Modeling, design, and analysis of interferometric cantilevers for time-resolved force measurements in tapping-mode atomic force microscopy

Cantilevers with interferometric high bandwidth force sensors can resolve nonlinear tip-sample interaction forces in tapping-mode atomic force microscopy. In this paper, we provide a detailed analysis of time-resolved force measurements using such cantilever. We first model the probe as a coupled spring-mass system and investigate its steady state dynamics under tapping-mode imaging conditions. Next, we analyze the optical response of the interferometric force sensor: Diffraction patterns as a function of tip displacement are obtained both analytically and by simulations. Finally, the frequency response of the force sensor is calculated, and the effects of the sensor geometry variations on the sensor mechanical response are analyzed.

Cost-efficient drilling using industrial robots with high-bandwidth force feedback

Here we present a method for high-precision drilling using an industrial robot with high-bandwidth force feedback, which is used for building up pressure to clamp-up an end-effector to the work-piece surface prior to drilling. The focus is to eliminate the sliding movement (skating) of the end-effector during the clamp-up of the end-effector to the work-piece surface, an undesired effect that is due to the comparatively low mechanical stiffness of typical serial industrial robots. This compliance also makes the robot deflect due to the cutting forces, resulting in poor hole position accuracy and to some extent in poor hole quality. Recently, functionality for high-bandwidth force control has found its way into industrial robot control systems. This could potentially open up the possibility for robotic drilling systems with improved performance, using only standard systems without excessive extra hardware and calibration techniques. Instead of automation with expensive fixtures and precise machinery, our approach was to make use of standard low-cost robot equipment in combination with sensor feedback. The resulting sliding suppression control results in greatly improved hole positioning and quality. The conceptual idea behind the force control is useful also in many other robotic applications requiring external sensor feedback control.

Analysis and control of monolithic piezoelectric nano-actuator

This paper describes the analysis and control of a two degree-of-freedom (DOF) monolithic piezoelectric actuator. This actuator is part of a six-DOF manipulator capable of linear resolution to 2 nm and angular resolution to 1 arc-second. Design of this actuator differs from the existing ones in that it has a monolithic structure which enables a high bandwidth, low drift, and high force realization. A number of nonlinearities exist in the actuator, stemming from the geometry and material properties. For example, coupling of the actuator elements can be modeled as a soft spring which increases displacement/drive-voltage gain (scale factor) at high actuation levels. In this work, a combination of feedforward (amplitude-dependent command prefiltering/input shaping) and feedback control are applied to reduce the effects of 1) scale factor nonlinearities; 2) hysteresis; and 3) output oscillations.

Parallel-Coupled Micro-Macro Actuators

This paper presents a new actuator system consisting of a micro- actuator and a macro-actuator coupled in parallel via a compliant transmission. The system is called the parallel-coupled micro-macro actuator, or PaCMMA. In this system, the micro-actuator is capable of high-bandwidth force control owing to its low mass and direct-drive connection to the output shaft. The compliant transmission of the macro-actuator reduces the impedance (stiffness) at the output shaft, and increases the dynamic range of force. Performance improvement over single- actuator systems was expected in force control, impedance control, force distortion, and transient impact force reduction. Several theoretical performance limits are derived from the sat uration limits of the system. A control law is presented. A prototype test bed was built and an experimental comparison was performed between this actuator concept and two single-actuator systems. A set of quantitative measures is proposed and the actuator system is evaluated against them with the following results: force bandwidth of 56 Hz, torque dynamic range of 800: 1, peak torque of 1,040 mNm, and minimum torque of 1.3 mNm. Peak impactforce, fonce distortion, and back-driven impedance of the PaCMMA system are shown to be better than either of the single-actuator configurations considered.

High-bandwidth force and impedance control for industrial robots

Common geared industrial robots call for force control methods with special properties such as good rejection of frictional disturbances, smoothness of corrective motions, and more. A new method is presented which meets these requirements and provides a high control bandwidth. In the manner of hybrid control, directions of a task frame can be selected to be force, impedance or position controlled. A joint-based inner position loop and a superimposed predictive force controller are used. Practical results include data from a robotic grinding facility. Here, the controller proved robustness and good performance under rough conditions.

High-Bandwidth Force Control for Industrial Robots

Common geared industrial robots call for force control methods with special properties such as good rejection of frictional disturbances, smoothness of corrective motions, and more. A new method is presented which meets these requirements and provides a high control bandwidth. A joint-based inner position loop and a superimposed predictive force controller are used. Practical results include data from a robotic grinding facility. Here, the controller proved robustness and good performance under rough conditions.

Force interactions in the synthetic environment using the isu force reflecting exoskeleton

With the increasing development of sophisticated computer graphic displays, attention has been focused on methods to provide force feedback to the human operator in the virtual environment. This work presents results from a prototype exoskeleton device for use in virtual reality force feedback systems. This design is based on the use of an electro-magnetic interface to couple a robotic exoskeleton with the human operator. In this system, a robotic mechanism provides an absolute link to ground and supports the weight of the actuation devices and tracking sensors. The mechanical link to ground allows the application of arbitrary interaction forces and provides the position, velocity, and force reference information needed to update graphical displays and generate accurate force feedback. An electromagnetic interface eliminates heavy and bulky mechanical attachments to the operator, and provides the capability for high bandwidth force application. By using a robotic manipulator to support the heavy parts of the system, the working range of motion is increased. The system provides the flexibility of producing a wide range of both relative forces between two fingers and absolute forces between fingers and the environment. This two-degree-of-freedom functional prototype is currently in the testing phase, and preliminary results show adequate motion tracking and force generation capabilities.

Force measurement using an inductively coupled sensor

A low-compliance, high-bandwidth force sensor is described. The bending of a quartz plate is converted to an analog voltage by using a phase-locked loop to measure the change in frequency of two oscillators inductively coupled to the plate. The resolution of the sensor is approximately 10(-5) N, with a bandwidth of approximately 1 kHz.