MEMS Gyroscopes
Verwandte Produkte: HF2LI, HF2LI-MF, HF2LI-MOD, HF2LI-PID, HF2LI-PLL, UHFLI, UHF-PID, HF2TA
Beschreibung der Anwendung
Die Drehbewegungsmessung ist wichtig für den Automobil- und Luftfahrtsektor sowie für GPS-Navigations- und Gesundheitsüberwachungssysteme. Heute können Gyroskope, die auf der Technologie mikroelektromechanischer Systeme (MEMS) basieren, so miniaturisiert werden, dass sie mit minimalem Stromverbrauch in Smartphones passen. Solche Systeme überwachen die Bewegung einer schwingungsfesten Masse, die durch eine federartige MEMS-Struktur an einem Montagerahmen befestigt ist, in allen Raumrichtungen. MEMS-Gyroskope werden oft mit Beschleunigungsmessern kombiniert und liefern dann sechsdimensionale Messungen von einem einzigen Gerät aus.
Die Testmasse wird oft gezwungen, mit Hilfe von Antriebselektroden (die den Antriebsmodus identifizieren) periodisch in einer Richtung zu schwingen. Sobald das Gerät eine Drehbewegung erfährt, erfährt die Masse die Corioliskraft in ihrer rotierenden Bezugsebene: Dies erscheint als eine leichte Verschiebung entlang einer Richtung, die senkrecht zu der durch den Antriebsmodus definierten Richtung verläuft, wie in der Abbildung dargestellt. Die Erfassung der Amplitude dieser Verschiebung (durch den so genannten Sensormodus) liefert die Winkeldrehrate. Diese Art von Drehbewegungsmessgerät wird oft als Coriolis-Vibrationskreisel (CVG) bezeichnet.
Measurement Strategies
Accurate rotation measurements with CVGs require a high level of control over both drive and sense modes. For this purpose, additional application-specific integrated circuitry (ASIC) is often developed.
Drive mode control
The first step is to force the mass to vibrate at its resonance along the drive mode using a phase-locked loop (PLL). An additional PID controller ensures that the drive mode has a constant amplitude by achieving automatic-gain-control (AGC). Together, the two feedback loops guarantee that the rotational motion does not affect the drive mode. Carrier modulation in amplitude or frequency can help to reject background noise and further parasitic contributions to gyroscopic measurements. Alternatively, parametric resonance can be performed using multiple demodulators synchronously and a parametric sweeper.
Open-loop sense mode configuration
In the open-loop configuration, a single output component of the demodulator monitors the sense mode; manual adjustment of the sense mode phase is required to retrieve an amplitude directly proportional to the angular rate. However, the amplitude decay time constant determined by the quality factor and the resonance frequency of the sense mode limits the gyroscope's response time to an input rotation.
Closed-loop sense mode configuration
Closed-loop control of the sense mode makes it possible to shorten the device's response time and increase the CVG's bandwidth and dynamic range. The closed-loop scheme produces a feedback force that suppresses motion in the sense mode. This force-to-rebalance method provides direct access to the input angular rate through the magnitude of the applied feedback force. The closed-loop sense mode configuration requires four control loops, three of which rely on PID controllers to build the feedback signal.
Product Highlights
The Benefits of Choosing Zurich Instruments
- All the gyroscope control strategies listed above can be seamlessly implemented and tested on your device with Zurich Instruments lock-in amplifiers, eliminating the need for time-consuming and expensive ASIC development. For example, the HF2LI Lock-in Amplifier offers 50 kHz PLL bandwidth and can thus reduce significantly the complexity of operation of a CVG – especially in the closed-loop sense configuration. For sensing applications requiring faster operation and higher control bandwidths, the UHFLI Lock-in Amplifier translates the capabilities of the HF2LI into frequencies up to 600 MHz (with 300 kHz PLL bandwidth).
- You can characterize drive and sense mode behavior, including backbone measurements, thanks to the time- and frequency-domain tools offered by the LabOne software.
- Zurich Instruments' analog electronics give access to differential voltage or current measurements (by combining the HF2LI with the HF2TA Current Amplifier), and offer multiple input stages to minimize the input noise and maximize the signal-to-noise ratio for periodic signals.
- Thanks to fast digital data transfer through USB or GbE connections, no additional digitizer card is required to record your measurement results.