Riccardo Antonello

Control of a Z-axis MEMS vibrational gyroscope

The paper describes the design of the control loops in a Z-axis, MEMS vibrational gyroscope. In this device, a silicon mass is driven through electrostatic actuator so that it has a sinusoidal linear motion, with a controlled speed. The design of a suitable controller, capable of maintaining the required speed and with prescribed restoring capabilities after shocks has been derived and described in the paper. Attached to the driving mass, a second mass, free to move in the direction orthogonal to the motion of the first mass, is subjected to a Coriolis force, proportional to the product of the first mass speed by Z-axis rotational speed. The sensing of the Coriolis force and, in turn, of the Z-axis rotational speed, is performed in closed loop fashion, with a 1-bit quantized actuation. The restoring force that brings the motion of the second mass to zero is equivalent to the output bit stream of a sigma-delta converter and contains the information of the Coriolis force. The design of this second control loop and a detailed analysis on the signal-to-noise ratio achievable with the proposed design is reported.

Automatic Mode Matching in MEMS Vibrating Gyroscopes Using Extremum-Seeking Control

In order to enhance the sensitivity and to reduce the readout circuit complexity of any angular velocity microsensor (vibrating gyroscope), it is crucial to reduce the frequency mismatch of its resonant modes of vibration. Achieving a good matching accuracy during fabrication is rather difficult because of tolerances and process variations that detrimentally affect the manufacturing precision. Moreover, even assuming to achieve a good frequency matching through fabrication or postfabrication calibration, it is very likely that parametric variations induced by the external environment during the normal operation of the device disrupt any initial tuning. For these reasons, in this paper, an alternative way to accomplish the frequency-matching condition is suggested, which exploits a real-time adjusting mechanism based on an automatic mode-matching control loop. In particular, this paper describes the details of an adaptive controller capable of automatically matching the resonant frequencies of the two main modes of vibration of a single-axis vibrating microgyroscope, under the provision that there is an underlying mechanism through which the frequency mismatch can be controlled by adjusting a suitable tunable parameter. The controller is designed by considering the requirement of reducing its complexity, so that it can be easily implemented on cheap sensors. Owing to a key observation that allows the recast of the frequency-matching problem as a maximization problem, the proposed mode-matching controller is actually designed as a standard perturbation-based extremum-seeking controller, which can be implemented by using few analog electronic components. The proposed solution has been tested on the LISY300AL yaw-rate microelectromechanical system gyroscope manufactured by STMicroelectronics, showing that a mode matching of nearly 1 Hz or less can be easily attained.

Maximum-Torque-Per-Ampere Operation of Anisotropic Synchronous Permanent-Magnet Motors Based on Extremum Seeking Control

This paper presents a theoretical analysis of a maximum-torque-per-ampere control strategy based on the extremum seeking control working principle, which provides useful insights for the definition of a systematic and quantitative design procedure. The focus is on the convergence properties to the optimal operating point, and a method for evaluating an upper bound of the convergence time is proposed. The analysis is supported by several experimental tests performed on an interior permanent-magnet synchronous motor.

A low-power 3-axis digital-output MEMS gyroscope with single drive and multiplexed angular rate readout

Motivated by the increasing demand of integrated inertial-sensing solutions for motion processing and dead-reckoning navigation in handheld devices and low-cost GPS navigators, this paper reports the details of a 3-axis silicon MEMS vibratory gyroscope that fulfills the pressing market requirements for low power consumption, small size and low cost. Thanks to a compact mechanical design that combines a triple tuning-fork structure within a single vibrating element, our solution achieves satisfactory performance in terms of thermal stability, cross-axis error, and acoustic noise immunity by using a small die size. Furthermore, the presence of a single primary vibration mode for the excitation of the 3 tuning-forks, together with the possibility of sensing the pickoff modes in a multiplexing fashion, allows to design a small-area, low-power ASIC.

Open loop compensation of the quadrature error in MEMS vibrating gyroscopes

This paper presents a simple, yet effective approach for rejecting the quadrature error in MEMS vibratory gyroscopes. The proposed solution consists of an open loop compensation that is performed on the proof-mass displacement readout signal provided by a standard capacitive sensing interface based on parallel-plate capacitors. The compensating signal is generated and calibrated according to the nominal quadrature error to reject, and is injected into the system by means of a compensation circuit based on a dynamically reconfigurable capacitor bank. The compensation scheme described in the paper has been implemented on ASIC and experimentally tested on a real MEMS vibratory gyroscope. Experimental results show that the proposed solution assures good rejection capabilities, even for very large quadrature errors that unavoidably saturates the sensor readout interface.

Exploring the Potential of MEMS Gyroscopes: Successfully Using Sensors in Typical Industrial Motion Control Applications

Since their conception in the 1990s, MEMS gyroscopes have gained increasing popularity over traditional mechanical or optical gyroscopes because of their innate features such as low cost, reduced size, and low power requirements. Market acceptance has grown over the years, thanks to the constant efforts spent by manufacturers in improving key features such as performance, reliability, and cost of the single device. Recently, MEMS gyroscopes have begun to be applied in several automotive, industrial, and consumer electronics applications either as replacements of older, bulkier, and more expensive sensors or as essential components in new applications that require compact, inexpensive solutions for the measurement of the angular rate. Typical motion control applications, such as the stabilization of inertial platforms, the active damping of undesired vibrations, or the motion reconstruction, can undoubtedly benefit from the usage of MEMS gyroscopes. The two motion control applications presented in this article portray, with the support of real experimental data, some of these benefits. Hopefully this article has provided sufficient motivations to the interested reader to further explore the potentials of MEMS gyroscopes and to start planning how to successfully apply them in existing or innovative motion control applications.

Hierarchical Scaled-States Direct Predictive Control of Synchronous Reluctance Motor Drives

This paper presents the design and experimental validation of a finite-state direct predictive control (DPC) for synchronous reluctance motor (SynRM) drives. The main features are the hierarchical selection policy of the optimal voltage vector and the dynamic scaling of the voltage amplitude, which keeps the current ripple limited even in the presence of low switching frequencies, as required by medium and high-power applications. The implementation is simple, intuitive, and low-demanding. This study is fully supported by experimental evidences.

Energy-Efficient Autonomous Solar Water-Pumping System for Permanent-Magnet Synchronous Motors

This paper presents a novel stand-alone solar-powered water-pumping system, especially suited for usage in rural or remote areas. The system is primarily designed to reduce both cost and complexity, while simultaneously guaranteeing optimal utilization of the photovoltaic generator. The use of standard hardware and control architectures ensures ease of installation, service, and maintenance. The proposed solution consists of a water pump driven by a permanent-magnet synchronous motor, controlled by a conventional field oriented control scheme. The photovoltaic array is directly connected to the dc bus of the inverter, with no intermediate power conversion stages. A perturbation based extremum-seeking controller adjusts the motor speed reference to attain the maximum power point operation of the photovoltaic array. Both simulations and experimental results on a full-scale prototype support the effectiveness of the proposed system.

Acceleration Measurement Drift Rejection in Motion Control Systems by Augmented-State Kinematic Kalman Filter

This paper deals with the use of MEMS accelerometers to improve the performances of positioning control systems equipped with low-resolution positioning sensors. A kinematic Kalman filter (KKF) is used to combine the position and acceleration measurements and get a smooth estimate of the kinematic variables, even in the presence of a coarse position quantization. Compared to similar schemes existing in literature, the state of the proposed KKF is augmented, to include the accelerometer output bias/drift among the variables estimated by the filter. In this way, the intrinsic robustness of the KKF scheme is further improved, by making the estimation process of the kinematic variables practically insensitive to the variation of the sensor bias/drift. The proposed KKF is used to provide a smooth and robust estimate of the kinematic variables to a positioning control system consisting of a two degrees-of-freedom (DOF) proportional-derivative (PD) position control combined with an acceleration-based disturbance observer (ADOB). Compared to a solution based on a conventional KKF, not accounting for the accelerometer output disturbance, the proposed solution exhibits better positioning performances, and insensitivity to the accelerometer output bias/drift. This feature is validated through several experimental tests on a positioning system based on a linear motor.

Benefits of Direct Phase Voltage Measurement in the Rotor Initial Position Detection for Permanent-Magnet Motor Drives

This paper shows how the problem of estimating the initial rotor position in permanent-magnet sensorless drives can benefit from the availability of a direct measurement of motor phase voltages. Two different estimation methods are presented for this purpose. The first is a readjustment of a classic procedure based on the detection, by means of the injection of voltage test pulses, of inductance variations due to motor saliencies, from which it is then possible to infer the position of the rotor. Since the application of irregular test pulses may increase the estimation uncertainties, the available voltage measurement is exploited to implement a closed-loop amplitude control of the test pulses. The second method is introduced both to overcome an issue related to the digital measurement approach adopted in this paper and to allow position estimation even in a motor with no relevant saliency, a case for which the first method is inappropriate. The effectiveness of the proposed solutions is validated by several experimental tests, which are carried out on two motors with different saliency properties.