Three-axis Force Sensor Research Articles

STRUCTURAL OPTIMISATION OF A FORCE-TORQUE SENSOR THROUGH ITS INPUT-OUTPUT RELATIONSHIP

This paper presents an advanced method to optimise the compliant structure of force-torque sensors at the design stage. To this end, some researchers used finite element analysis on the whole compliant structure or some of its components, while others proposed performance indices based on mechanism theory. This work proposes a new approach, which relies on a symbolic formulation of the wrench-displacement relationship, and by which we minimise the condition number of this linear input-output relationship. Our method is centered on the application requirements, thus, it takes into account constraints such as the measurement range, the maximum allowed compliance or maximum physical dimensions of the structure. Thus, the input-output relationship allows to match applied forces with sensor displacements to achieve a prescribed sensitivity. The resulting performance index can be expressed symbolically, which eases the synthesis task. The optimisation procedure, design, fabrication and experiments of a three-axis force sensor architecture are also presented to illustrate the theory.

Flexible three-axial force sensor for soft and highly sensitive artificial touch.

A soft tactile sensor able to detect both normal and tangential forces is fabricated with a simple method using conductive textile. Owing to the multi-layered architecture, the capacitive-based tactile sensor is highly sensitive (less than 10 mg and 8 μm, for minimal detectable weight and displacement, respectively) within a wide normal force range (potentially up to 27 N (400 kPa)) and natural touch-like tangential force ranges (from about 0.5 N to 1.8 N). Being flexible, soft, and low cost, this sensor represents an original approach in the emulation of natural touch.

Design and Fabrication of a Three-Axis Force Sensor for Underwater Robot Fingers and a Method for Decreasing Error

In this paper, we present a new mathematical model of three-axis force sensor for underwater robot fingers. We designed a kind of sensor based on this model which has a simple structure and can be miniaturized easily. By this model, they can be calculated that the magnitude, direction of finger force. Moreover, we present a new compensating method to decrease the error caused with the variation of temperature and pressure of water and caused with bending of the beams by symmetrical electronic circuits. We proposed compensation block method to solve the problem of heavy lead wire which affecting finger moving in underwater. Finally, an experiment is performed to verify the proposed model.

A self-decoupled three-axis force sensor for measuring the wheel force

The wheel force transducer is an important device in the automotive testing field which can measure the force or torque applied to the wheel. Because existing wheel force transducers are almost commercial products, they are too expensive and technical information about them has not been made public; this slows down the development of the wheel force transducer to a certain extent. Accordingly a three-axis wheel force transducer is presented in this paper which is self-decoupled without calculating the decoupling matrix in theory. Its elastic body has a spoke structure with eight elastic beams, which means that it is easy to fabricate. This paper first introduces the overall elastic body structure of the proposed wheel force transducer. Then the strain gauge arrangement, the principle of strain measurement, the connection modes of the bridge circuits and the rotation decoupling principle for Fx and Fz are analysed, and the self-decoupled characteristics are depicted in detail. Finally, to verify the validity of the designed wheel force transducer, three kinds of experiment are carried out. In the static experiments the static performance and the self-decoupled characteristics of the wheel force transducer are verified; in the dynamic tests, a vehicle dynamics test system is adopted to verify the accuracy of the wheel force transducer in the dynamic environment; in road tests, the sensor is installed in the vehicle to verify whether the output of the proposed wheel force transducer can reflect the variation in the force applied to the wheel in practical applications. The results shows the following: first, the maximum non-linearity error, the maximum hysteresis error and the maximum repeatability error of the proposed wheel force transducer are 0.9% of the full scale, 1.1% of the full scale and 0.5% of the full scale respectively; second, the static coupling rate is about 0.08%, which means that the designed wheel force transducer is self-decoupled in theory; third, the proposed wheel force transducer can measure Fx, Fz and My effectively in real applications.

손목굽힘운동 재활로봇을 위한 3축 힘센서 설계

Most serious stroke patients have the paralysis of their wrists, and can't use of their hands freely. But their wrists can be recovered by rehabilitation exercise. Recently, professional rehabilitation therapeutists exercise the wrists of stroke patients in hospital. But the wrists of stroke patients have not rehabilitated, because the therapeutists are much less than stroke patients in number. Therefore, the wrist bending-exercise rehabilitation robot that can measure the bending force of the patients' wrists is developed. In this paper, the three-axis force sensor was designed for the wrist bending-exercise rehabilitation robot. As a test results, the interference error of the three-axis force sensor was less than 0.85%. It is thought that the sensor can be used to measure the wrist bending force of the patient.

Polymer-based flexible capacitive sensor for three-axial force measurements

We have developed a flexible-substrate-based three-axial force sensor, composed of finger-shaped electrode capacitors, whose operation is based on the measurement of a capacitance change induced upon applying a three-axial load. The electrode design supports high sensitivity to shear forces. An overall flexibility of the sensor and elasticity of the capacitor's dielectric is obtained by integrating three polymers in the sensor's technology process, namely polyimide, parylene-C, and polydimethylsiloxane, combined with standard metallization processes. We have theoretically modeled the sensor's capacitance and its three-axial force sensitivity. The unit capacitors have static capacitances in the range of 20 pF. The electro-mechanical characterization of the capacitors reveals in the normal direction a sensitivity Sz = 0.024 kPa−1 for pressures <10 kPa, whereas for higher pressures the measured sensitivity Sz = 6.6 × 10−4 kPa−1. Typical measured shear force sensitivity Sx = 2.8 × 10−4 kPa−1. These values give our transducer high potential for use in skin-like sensing applications.

Control of Fingertip Forces in Young and Older Adults Pressing against Fixed Low- and High-Friction Surfaces

Mobile computing devices (e.g., smartphones and tablets) that have low-friction surfaces require well-directed fingertip forces of sufficient and precise magnitudes for proper use. Although general impairments in manual dexterity are well-documented in older adults, it is unclear how these sensorimotor impairments influence the ability of older adults to dexterously manipulate fixed, low-friction surfaces in particular. 21 young and 18 older (65+ yrs) adults produced maximal voluntary contractions (MVCs) and steady submaximal forces (2.5 and 10% MVC) with the fingertip of the index finger. A Teflon covered custom-molded splint was placed on the fingertip. A three-axis force sensor was covered with either Teflon or sandpaper to create low- and high-friction surfaces, respectively. Maximal downward forces (Fz) were similar (p = .135) for young and older adults, and decreased by 15% (p<.001) while pressing on Teflon compared to sandpaper. Fluctuations in Fz during the submaximal force-matching tasks were 2.45× greater (p<.001) for older adults than in young adults, and reached a maximum when older adults pressed against the Teflon surface while receiving visual feedback. These age-associated changes in motor performance are explained, in part, by altered muscle activity from three hand muscles and out-of-plane forces. Quantifying the ability to produce steady fingertip forces against low-friction surfaces may be a better indicator of impairment and disability than the current practice of evaluating maximal forces with pinch meters. These age-associated impairments in dexterity while interacting with low-friction surfaces may limit the use of the current generation of computing interfaces by older adults.

A Three-Axis Force Sensor for Dual Finger Haptic Interfaces

In this work we present the design process, the characterization and testing of a novel three-axis mechanical force sensor. This sensor is optimized for use in closed-loop force control of haptic devices with three degrees of freedom. In particular the sensor has been conceived for integration with a dual finger haptic interface that aims at simulating forces that occur during grasping and surface exploration. The sensing spring structure has been purposely designed in order to match force and layout specifications for the application. In this paper the design of the sensor is presented, starting from an analytic model that describes the characteristic matrix of the sensor. A procedure for designing an optimal overload protection mechanism is proposed. In the last part of the paper the authors describe the experimental characterization and the integrated test on a haptic hand exoskeleton showing the improvements in the controller performances provided by the inclusion of the force sensor.

1P1-I02 多指ハンドシステムの開発と指先による物体操作(ロボットハンドの機構と把持戦略(3))

In this research, we have developed a multi-fingered hand system to control an object in a real environment using simulation results that are obtained from motion planning for object manipulation. The hand has four fingers each of which has three or four joints and a three-axis force sensor on its fingertip. The system hardware consists of a personal computer, a PIC microcontroller, a PSoC chip, analog-to-digital converter chips, force sensors, servo motors and mechanical links. Motion planning is based on rolling contact, stable grasp and re-grasping. We have verified that the robot hand has the ability of performing object manipulations that are nearly the same as the simulation results.

Evaluation of the perceived elasticity of sheepskin using a three-axis force sensor system

Sheepskin refers to the hide taken from a sheep and is composed of a layer of skin and the attached hair. It has unique fabric handle properties, and sheepskin quality assessments generally depend on a subjective hand evaluation via sensory test. Therefore, it is necessary to measure the fabric handle of sheepskin mechanically. For this study, we focused on perceived elasticity, and attempted to clarify the relationship between the tactile sensation and the mechanical properties of sheepskin through the development of a new three-dimensional tactile sensation measurement system (3D-TSMS) to measure the compression properties in three axial directions. For compression testing, the compression parameters were calculated as follows: compression linearity ( LC), compressional energy ( WC), compressional resilience ( RC), compressional flexibility coefficient ( αmax), pressure relieving energy (Δ EPR), and continuous mean deviation ( CMD), etc. As a result of compression testing, the sheepskin samples which were highly rated for their perceived elasticity showed a convex curve during the initial compression process. In the statistical comparison analysis, LC, CMD, and Δ EPR showed a correlation to the perceived elasticity of sheepskin.

단축 힘센서를 이용한 두 손가락 잡기 힘측정장치 개발 및 특성평가

Finger patients can't use their hands because of the paralysis their fingers. Their fingers are recovered by rehabilitating training, and the rehabilitating extent can be judged by measuring the pressing force to be contacted with two fingers(thumb and first finger, thumb and middle finger, thumb and ring finger, thumb and little finger). At present, most hospitals have used a thin plastic-plate for measuring the two-finger grasping force, and we can only judge that they can grasp the plate with their two-finger through it, because the plate can't measure the two-finger grasping force. But, recently, the force measuring system for measuring two-finger grasping force was developed using three-axis force sensor, but it is very expensive, because it has a three-axis force sensor. In this paper, two-finger force measuring system with a one-axis force sensor which can measure two-finger grasping force was developed. The one-axis force sensor was designed and fabricated, and the force measuring device was designed and manufactured using DSP(Digital Signal Processing). Also, the grasping force test of men was performed using the developed two-finger force measuring system, it was confirmed that the grasping forces of men were different according to grasping methods, and the system can be used for measuring two-finger grasping force.

3축 힘센서를 이용한 두 손가락 힘측정장치 개발

Stroke patients can`t use their hands because of the paralysis their fingers. Their fingers are recovered by rehabilitating training, and the rehabilitating extent can be judged by measuring the pressing force to be contacted with two fingers (thumb and first finger, thumb and middle finger, thumb and ring finger, thumb and little finger). But, at present, the grasping finger force of two-finger can`t be accurately measured, because there is not a proper finger-force measuring system. Therefore, doctors can`t correctly judge the rehabilitating extent. So, the finger-force measuring system which can measure the grasping force of two-finger must be developed. In this paper, the finger-force measuring system with a three-axis force sensor which can measure the pressing force was developed. The three-axis force sensor was designed and fabricated, and the force measuring device was designed and manufactured using DSP (Digital Signal Processing). Also, the grasping force test of men was performed using the developed finger-force measuring system, it was confirmed that the grasping forces of men were different according to grasping methods.

3축 힘센서를 이용한 구물체 잡기 손가락 힘측정시스템 개발

Stroke patients can`t use their hands because of the paralysis of their fingers. Their fingers are recovered by rehabilitating training, and the rehabilitating extent can be judged by grasping a spherical object. At present, the object used in hospital is only a spherical object, and can`t measure the force of fingers. Therefore, doctors judge the rehabilitating extent by touching and watching at their fingers. So, the spherical object measuring system which can measure the force of their fingers should be developed. In this paper, the finger-force measuring system with a three-axis force sensor which can measure the spherical-object grasping force is developed. The three-axis force sensor is designed and fabricated, and the force measuring device is designed and manufactured using DSP(digital signal processing). Also, the grasping force test of men is performed using the developed finger-force measuring system, it was confirmed that the average force of men was about 120 N.

Capacitive Sensor for Three-Axis Force Measurements and Its Readout Electronics

A capacitive sensor that can detect both vertically and horizontally applied contact forces is proposed. The sensor is built on a flexible material (rubber), in which conductive materials are deposited, forming four separate variable capacitors. The overall result is a thin sensor that consists of four variable capacitors with increased mechanical flexibility and robustness and is characterized by a simple structure and manufacture. The interface electronics, which allows reducing the parasitic capacitance effects of the wires, is also described. The experimental tests performed in the aforementioned setup demonstrate that the three-axis capacitive force sensor and its readout circuit are valid concepts to be applied to several fields, ranging from health to robotics, among others.

3축 손가락 힘센서를 가진 지능로봇의 지능형 로봇손 개발

This paper describes the intelligent robot's hand with three-axis finger force sensors for an intelligent robot. In order to grasp an unknown object safely, it should measure the mass of the object, and determine the grasping force using the mass, then control the robot's fingers with the grasping force. In this paper, the intelligent robot's hand for an intelligent robot was developed. First, the three-axis finger force sensors were designed and manufactured, second, the intelligent robot's hand with three-axis finger force sensors were designed and fabricated, third, the high-speed control system was designed and manufactured using DSP( digital signal processor), finally, the characteristic test to grasp an unknown object safely was carried out. It was confirmed that the developed intelligent robot's hand could grasp an unknown object safely.

A Physics Road Rally

Our school recently acquired1 Vernier's Wireless Dynamics Sensor System (WDSS). The WDSS consists of a three-axis accelerometer, altimeter, and force sensor that has the ability to remotely collect data for later transfer to a computer.2 While our primary purpose for acquiring the WDSS was to enhance our amusement park physics experiments, we decided to test one of the WDSS units by using it to collect data during the drive home from school one day, since measuring the acceleration of a car is one of the experiments suggested in the Vernier Wireless Dynamics Sensor System User Manual. We taped the device to the floor of the car with its +x-axis pointed forward and its +y-axis pointed to the left. The WDSS was configured to take five samples per second for a total time period of 10 minutes.

Friction-Based &lt;i&gt;In Situ &lt;/i&gt;Endpoint Detection of Copper CMP Process

Chemical mechanical polishing (CMP) has been extensively used in the integrate circuit (IC) manufacturing industry as a widely accepted global planarization technology, accurate in situ endpoint detection of CMP process can reduce the product variance, significantly improve yield and throughput. A CMP in situ endpoint detection system, which measured the friction and downforce during CMP process using a specially designed three-axis strain gauge force sensor, was developed. The frictional transition from copper (Cu) to tantalum (Ta) barrier as well as Ta barrier to silicon dioxide (SiO2) dielectric was detected during CMP process. The experimental results showed that the change of friction could be detected when the polished material changed. The developed CMP in situ endpoint detection system is feasible for 300 mm and 450 mm copper CMP process.

Bio-inspired sensorization of a biomechatronic robot hand for the grasp-and-lift task

It has been concluded from numerous neurophysiological studies that humans rely on detecting discrete mechanical events that occur when grasping, lifting and replacing an object, i.e., during a prototypical manipulation task. Such events represent transitions between phases of the evolving manipulation task such as object contact, lift-off, etc., and appear to provide critical information required for the sequential control of the task as well as for corrections and parameterization of the task. We have sensorized a biomechatronic anthropomorphic hand with the goal to detect such mechanical transients. The developed sensors were designed to specifically provide the information about task-relevant discrete events rather than to mimic their biological counterparts. To accomplish this we have developed (1) a contact sensor that can be applied to the surface of the robotic fingers and that show a sensitivity to indentation and a spatial resolution comparable to that of the human glabrous skin, and (2) a sensitive low-noise three-axial force sensor that was embedded in the robotic fingertips and showed a frequency response covering the range observed in biological tactile sensors. We describe the design and fabrication of these sensors, their sensory properties and show representative recordings from the sensors during grasp-and-lift tasks. We show how the combined use of the two sensors is able to provide information about crucial mechanical events during such tasks. We discuss the importance of the sensorized hand as a test bed for low-level grasp controllers and for the development of functional sensory feedback from prosthetic devices.

Development of a three-axis gripper force sensor and the intelligent gripper using it

This paper describes the development of a three-axis gripper force sensor that measure forces F x , F y and F z simultaneously, and the intelligent gripper using two three-axis gripper force sensors for grasping an unknown object stably. In order to grasp an unknown object using an intelligent gripper safely, it should measure the forces in the grasping direction and in the gravity direction, and perform the force control with the measured forces. Thus, the intelligent gripper should be composed of two three-axis gripper force sensors that measure forces F x , F y and F z at the same time. In this paper, two three-axis gripper force sensors for measuring forces F x , F y and F z simultaneously were newly modeled using five parallel plate-beams, designed, and fabricated. The characteristic tests of the manufactured sensors were carried out, and their interference errors of the developed sensors were less than 3%. Also, the intelligent gripper was manufactured using two three-axis gripper force sensors, and their characteristic tests were carried out. It was conformed that the developed gripper could grasp an unknown object stably.

High frequency bandwidth measurements of micro cutting forces

The miniaturization of machine components is perceived by many as a core requirement for the future technological development of a broad spectrum of products. One of the challenges in micro engineering is the development of economical micro systems that are flexible, functional and made of appropriate engineering materials. The mechanical removal of materials using miniature tools, known as a micro machining process, has unique advantages in creating 3D components using a variety of engineering materials, when compared with photolithographic processes. Since the diameter of miniature tools is very small, excessive forces and vibrations will significantly affect the overall part and tool quality. In order to improve the part and tool quality, accurate measurement of micro cutting forces is imperative. In this paper, we focus on the development of an ultra precision micro milling system and the measurement of micro cutting forces using a three-axis miniature force sensor and accelerometers. Since the inherent dynamics of the workpiece and overall machine tool affects the frequency bandwidth, we employ the Kalman filter approach to fuse the sensor signals and compensate for unwanted dynamics, in order to increase the bandwidth of the force measurement system. Based on accurate cutting force measurement, we can come up with the optimal process parameters to maintain desired tolerances and also monitor the process to prevent failures.