Technical noteMethod for evaluating the electrical and mechanical characteristics of a voice coil actuator
Introduction
Recently, a high-precision control of linear actuators is required in various industrial and research applications [1], [2], [3], [4]. For realizing the high-precision control, high-precision measurements and high-precision models are required. However, there are some difficulties in evaluating the electrical and mechanical characteristics of linear actuators using conventional testers. In such testers, the force generated by the actuator under test is measured using a force transducer, and the position of the actuator is measured using a position transducer.
However, the force transducers are typically calibrated by standard static methods using static weights under static conditions [5]. At present, there are no standard methods of evaluating the dynamic characteristics of the force transducers. This leads to two major problems in material testing: (1) it is difficult to evaluate the uncertainty in the measured varying force and (2) it is difficult to evaluate the uncertainty in the moment at which the varying force is measured.
Although methods to dynamically calibrate force transducers are not yet well established, there have been several attempts to develop such methods [5], [6], [7], [8]. The author has proposed a method, the “levitation mass method” (LMM). In this method, the inertial force of a mass levitated using a pneumatic linear bearing [9] is used as the reference force applied to the objects being tested, such as force transducers, materials, and structures. The inertial force of the levitated mass is measured using an optical interferometer. The author has also modified the basic method to suit the dynamic force calibration of force transducers against some typical dynamic forces, such as an impact force [5], [6], step force [7], and oscillation force [8]. However, it is not yet known how to apply the results of such dynamic calibration to the actual wave profile of a varying force. This difficulty derives mainly from the fact that the validity of applying the frequency response obtained from the oscillation force calibration to the other types of forces such as the impact force and step force has not been proved and is quite unlikely. In other words, it has not been proved that the frequency responses can be linearly superposed and that the response to any arbitrary force can be estimated from the transfer function of the system obtained using the impact, step, or frequency response methods.
On the other hand, the author has also applied the LMM to material testing, e.g., to the evaluation of the viscoelasticity of materials under a small impact load [10] and a forced oscillation load [11]. The LMM has been proved to be a very accurate and efficient method of measuring a varying force based on the standard definition of force, i.e., the product of mass and acceleration.
In this paper, a novel method for evaluating the electrical and mechanical characteristics of a voice coil actuator is proposed based on the LMM, and its performance is demonstrated.
Section snippets
Experimental setup
Fig. 1 shows a schematic diagram of the experimental setup for evaluating the electrical and mechanical characteristics of a voice coil actuator. A voice coil actuator (model: VCM26-02R; manufactured by Showa Electric Wire and Cable Co., Ltd., Japan) is connected to the moving part of an aerostatic linear bearing (model: Air-Slide TAAG10A-02; manufactured by NTN Co., Ltd., Japan). A cube-corner (CC) prism (for the interferometer) and some metal blocks (used for connecting the mass with the
Results and discussions
Fig. 2 shows the mechanical quantities measured during the experiment. First, the frequency is calculated from the digitized output signal of the optical interferometer and then the velocity, position, acceleration, force, and mechanical power are calculated from the frequency. In the figure, approximately 8 periods of the reciprocating motion are observed.
Fig. 3 shows the electrical quantities measured during the experiment. Although the function generator supplies a square wave of 35 Hz to the
Conclusions
A novel method for evaluating the electrical and mechanical characteristics of a voice coil actuator is proposed based on the LMM. Using the proposed method, the electrical and mechanical characteristics of a voice coil actuator are accurately determined.
Acknowledgements
This study was supported by a research aid fund of the Japan Science and Technology Agency (JST) and a research aid fund of the Japan Space Forum (JSF). The author thanks Prof. S. Hashimoto and Prof. T. Ishikawa at Gunma University for useful discussions.
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