A New Method for Measuring the Rotational Angles of a Precision Spherical Joint Using Eddy Current Sensors.
TL;DR: Results show that the root mean square angular error of a single axis within a range of ±14° is approximately 20 min, which suggests the feasibility of the proposed method.
Abstract: Precision spherical joint is a spherical motion pair that can realize rotation with three degrees of freedom. This joint is widely used in robots, parallel mechanisms, and high-end medical equipment, as well as in aerospace and other fields. However, the rotation orientation and angle cannot be determined when the joint is in passive motion. The real-time determination of the rotation orientation and angle is crucial to the improvement of the motion control accuracy of the equipment where the joint is installed in. In this study, a new measurement method that utilizes eddy current sensors is proposed to identify the special features of the joint ball and realize angle measurements indirectly. The basic idea is to manufacture the specific shape features on the ball without affecting its movement accuracy and mechanical performance. An eddy current sensor array is distributed in the ball socket. When the ball head rotates, the features on the ball opposite to the sensor, as well as the output signal of every eddy current sensor, change. The measurement model that establishes the relationship between the output signal of the eddy current sensor array and the rotation direction and angle of the ball head is constructed by learning and training an artificial neural network. A prototype is developed using the proposed scheme, and the model simulation and feasibility experiment are subsequently performed. Results show that the root mean square angular error of a single axis within a range of ±14° is approximately 20 min, which suggests the feasibility of the proposed method.
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TL;DR: Zhang et al. as mentioned in this paper proposed a measurement method for the rotation angle of the spherical joint based on the extreme learning machine (ELM) artificial neural network and four eddy current sensors.
Abstract: This paper proposes a measurement method for the rotation angle of the spherical joint based on the extreme learning machine (ELM) artificial neural network and four eddy current sensors. Aiming at the problems of small range and low accuracy in the early three-eddy-current angle measurement prototype, the position matching scheme of four eddy current sensors is researched, a new prototype is developed through simulation analysis, and ELM neural network substitutes the previous generalized regression neural network (GRNN) for building a new measurement model. The modelling training and comparison test are completed in the self-developed high-precision angle calibration device. Experimental results show that the new prototype not only covers a ±20° measurement range but also promotes measurement accuracy, and the standard deviation of the single-axis measurement drops to $3^{\prime }$ within the range of 5°–15°. It provides a relatively high-precision measurement method for real-time, multi-axis active detection of spherical joint space rotation angle error.
6 citations
TL;DR: In this paper , a pseudorandom code is used to generate a 2D plane absolute code and then mapped to the sphere, which is formed on the ball head through precision cutting, and an eddy current sensor array is arranged in the ball socket to identify the code.
2 citations
TL;DR: In this article , the influence of the magnetic field of an active magnetic bearing (AMB) on the eddy-current sensor operation was investigated and no significant influence of generated magnetic field from the support was found for the sensor output.
Abstract: This paper presents laboratory results on the influence of the magnetic field of an active magnetic bearing (AMB) on the eddy-current sensor operation. The magnetic suspension technology enables continuous diagnostics and monitoring of a rotary machine and eliminates drawbacks of classical bearing properties. The magnetic bearing system usually consists of two radial and one axial magnetic bearing. It is combined with a control unit, amplifiers and sensors for measuring the instantaneous position of the shaft. For this purpose, eddy-current sensors are frequently used. They operate in close proximity to the electromechanical actuators; therefore, the question arises whether the actuators do not interfere with the correct operation of these sensors. In the paper, the test rig and research plan prepared for that investigation are delivered. Measurement signals were registered from four control channels for different configurations of power supplies for system elements, e.g., with sensors and AMBs turned off, with sensors turn on and at normal work. Recorded time courses are presented and discussed in the paper. For the prepared test rig and AMB/eddy-current sensor configuration, no significant influence of the generated magnetic field from the support is found for the eddy-current sensor output.
1 citations
TL;DR: In this article , a two-axis angular experimental device was designed to measure the performance of a ball joint capacitive sensor in a frame stabilisation mechanism in an aeronautical optoelectronic pod, and a mathematical model to compensate for ball joint sensor installation error was created and tested.
Abstract: The ball joint is a multi-degree-of-freedom transmission pair, if it can replace the inner frame in the aviation photoelectric pod to carry the optical load, which will greatly simplify the system structure of the photoelectric pod and reduce the space occupied by the inner frame. However, installation errors in ball joint siting introduce nonlinear errors that are difficult to correct and two degree of freedom angular displacement of the ball joint is difficult to detect, which limits application in the precision control of two degrees of freedom systems. Studies of spherical capacitive sensors to date have not tested sensors for use in an inner frame stabilisation mechanism nor have they analysed the influence of installation error on sensor output. A two-axis angular experimental device was designed to measure the performance of a ball joint capacitive sensor in a frame stabilisation mechanism in an aeronautical optoelectronic pod, and a mathematical model to compensate for ball joint capacitive sensor installation error was created and tested. The experimental results show that the resolution of the capacitive sensor was 0.02° in the operating range ±4°, the repeatability factor was 0.86%, and the pulse response time was 39 μs. The designed capacitive sensor has a simple structure, high measurement accuracy, and strong robustness, and it can be integrated into ball joint applications in the frames of aeronautical photoelectric pods.
1 citations
TL;DR: The experimental results show that the realized prototype works properly with extremely low supply voltages, allowing for obtaining an ultra-low power consumption, significantly lower than other state-of-the-art solutions.
Abstract: The demand for smart, low-power, and low-cost sensors is rapidly increasing with the proliferation of industry automation. In this context, an Ultra-Low Power Eddy Current Displacement Sensor (ULP-ECDS) targeting common industrial applications and designed to be embedded in wireless Industrial Internet of Things (IIoT) devices is presented. A complete characterization of the realized ULP-ECDS operating with different metallic targets was carried out. The choice of the considered targets in terms of material and thickness was inspired by typical industrial scenarios. The experimental results show that the realized prototype works properly with extremely low supply voltages, allowing for obtaining an ultra-low power consumption, significantly lower than other state-of-the-art solutions. In particular, the proposed sensor reached the best resolution of 2 µm in case of a carbon steel target when operated with a supply voltage of 200 mV and with a power consumption of 150 µW. By accepting a resolution of 12 µm, it is possible to further reduce the power consumption of the sensor to less than 10 µW. The obtained results also demonstrate how the performances of the sensor are strongly dependent on both the target and the demodulation technique used to extract the displacement information. This allowed for defining some practical guidelines that can help the design of effective solutions considering application-specific constraints.
1 citations
Cites background from "A New Method for Measuring the Rota..."
...Among others, displacement sensors have an important role in many applications like the monitoring of Active Magnetic Bearings, AMBs, [1,2] gas turbine engines, [3], Blade Tip Clearance (BTC) in aero-engines [4], or the measurement of rotational angles in precision spherical joints [5]....
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References
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TL;DR: An overview of the fundamentals and main variables of eddy current testing is included, and the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems are described.
Abstract: Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future.
683 citations
"A New Method for Measuring the Rota..." refers background in this paper
...The eddy current sensor is widely used in the metal, nuclear, and aircraft industries; it can inspect electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensors [20]....
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TL;DR: In this paper, the design and commutation of a novel kind of spherical stepper motor with permanent magnets was addressed. But the rotor and stator poles were not arranged in order to interact to cause motion.
Abstract: This paper addresses the design and commutation of a novel kind of spherical stepper motor in which the poles of the stator are electromagnets and the poles of the rotor (rotating ball) are permanent magnets. Due to the fact that points on a sphere can only be arranged with equal spacing in a limited number of cases (corresponding to the Platonic solids), design of spherical stepper motors with fine rotational increments is fundamentally geometrical in nature. We address this problem and the related problem of how rotor and stator poles should be arranged in order to interact to cause motion. The resulting design has a much wider range of unhindered motion than other spherical stepper motor designs in the literature. We also address the problem of commutation, i.e., we determine the sequence of stator polarities in time that approximate a desired spherical motion.
230 citations
"A New Method for Measuring the Rota..." refers background in this paper
...The results showed that the measurement accuracy reached 1◦ [3,4]....
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TL;DR: In this article, the authors describe the design and control of a new version of a spherical permanent magnet actuator, which is capable of three degrees of freedom and a high specific torque.
Abstract: The paper describes the design and control of a new version of a spherical permanent magnet actuator, which is capable of three degrees of freedom and a high specific torque. Based on an analytical magnetic field distribution, the torque vector and back-emf are derived in closed forms. An optimal design procedure is proposed to achieve maximum output torque or maximum acceleration for a given payload. The control of the actuator, whose dynamics are similar to those of robotic manipulators, is facilitated by the establishment of a complete actuation system model and the application of the computed torque control law. The validity of the analysis and design techniques, and the effectiveness of the control strategy, are confirmed by measurements.
155 citations
"A New Method for Measuring the Rota..." refers methods in this paper
...The changes in the magnetic field in space were measured by configuring multiple sensors when the rotor rotated, and the position information of the rotor was obtained using the spatial mathematical operation of the data [6]....
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TL;DR: In this paper, the dynamic modeling and the control strategy of a three degree-of-freedom (DOF) variable-reluctance (VR) spherical motor are presented.
Abstract: Examination of existing joint designs for robot wrist applications has indicated that a spherical wrist motor offers a major performance advantage in trajectory planning and control as compared to the popular three-consecutive-rotational joint wrist. The tradeoff, however, is the complexity of the dynamic modeling and control. This paper presents the dynamic modeling and the control strategy of a three degree-of-freedom (DOF) variable-reluctance (VR) spherical motor which presents some attractive possibilities by combining pitch, roll, and yaw motion in a single joint. The spherical motor dynamics consist of the rotor dynamics and a torque model. The torque model is described as a function of coil excitations and a permeance model in terms of the relative position between the rotor and the stator. Both the forward dynamics which determine the rotor motion as a result of activating the electromagnetic coils and the inverse model which determines the coil excitations required to generate the desired torque are derived in this paper. The solution to the forward dynamics of the spherical motor is unique, but the inverse model has many solutions and therefore an optimization is desired. Experimental results verifying the dynamic model are presented. The control of a VR spherical motor consists of two parts ; namely, the control of the rotor dynamics with the actuating torque as system input, and the determination of the optimal electrical inputs for a specified actuating torque. The simulation results and implementation issues in determining the optimal control input vectors are addressed. It is expected that the resulting analysis will serve as a basis for dynamic modeling, motion control development, and design optimization of the VR spherical motor.
83 citations
Patent•
20 Nov 2007
TL;DR: In this paper, a coordinate measurement apparatus includes an articulated arm having a first end and a second end with at least a first arm segment and another arm segment there between, and a measurement probe attached to the first end of the articulated arm.
Abstract: In one embodiment, a coordinate measurement apparatus includes an articulated arm having a first end and a second end with at least a first arm segment and a second arm segment therebetween. Further, the apparatus can comprise at least one ball and socket joint connecting the first arm segment to the second arm segment, with the ball and socket joint including a ball member and a socket member, and a measurement probe attached to the first end of said articulated arm.
79 citations