FIELD OF THE DISCLOSURE

This disclosure relates to microelectromechanical (MEMS) gyroscopes, and more particularly to piezoelectrically driven and sensed z-axis gyroscopes, where proof masses move in the device plane in both their primary mode and their secondary mode. The present disclosure further concerns arrangements for reducing coupling between the primary and secondary modes by suitable placement and interconnection of piezoelectric drive and sense transducers around the periphery of the proof masses.

BACKGROUND OF THE DISCLOSURE

MEMS gyroscopes typically include proof masses which are driven into either linear or rotational oscillating motion, or a combination of these two motions. In z-axis MEMS gyroscopes, the primary oscillation induced by drive transducers is configured to occur in the substrate plane. If the gyroscope undergoes angular rotation about the z-axis, which is perpendicular to the substrate plane, the resulting secondary oscillation induced by the Coriolis force also will also occur in the substrate plane.

The partly mobile proof masses, which constitute the rotation-sensitive elements of the gyroscope, may be suspended from a fixed structure by suspenders which are configured to flexibly allow oscillating drive motion and sense motion at a desired resonant frequency. The net reaction force and torque of the drive oscillation mode and sense oscillation mode should preferably be zero, so that kinetic energy does not leak from these desired oscillation modes and external vibrations do not couple to them.

It is known that a gyroscope where a pair of interconnected proof masses are synchronized to continuously oscillate in opposite directions is less vulnerable to disturbances caused by external vibrations than gyroscopes with only one oscillating proof mass. This is because the effect of the disturbance can be automatically cancelled by reading the measurement signal in a differential manner. It is also known that further robustness can be achieved with an additional pair of proof masses which oscillates orthogonally to the first.

However, a general problem in z-axis gyroscopes with coupled proof mass pairs is that the primary oscillation may be coupled into the secondary oscillation or the secondary signal, so that each oscillation cycle in the primary mode also generates simultaneous oscillation in the secondary mode or a signal in the transducers that are disposed to detect the secondary oscillation. Asymmetries in any part of a MEMS gyroscope can give rise to coupling effects, and some degree of asymmetry is unavoidable since manufacturing tolerances can never be reduced to zero. The suspension arrangements from which proof mass pairs are suspended should therefore preferably be designed to flexibly allow both the primary and the secondary oscillation mode, but to resist coupling between these two modes.

Document US2016341551 discloses a MEMS gyroscope with multiple pairs of proof masses in oscillation around a crossing point. A problem with the suspension arrangement disclosed in this document is that it does not prevent coupling between the primary and the secondary mode.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide an apparatus for to alleviate the above disadvantages.

The object of the disclosure is achieved by an arrangement which is characterized by what is stated in the independent claim. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of forming a gyroscope with piezoelectric drive and sense transducers placed on a suspender with the shape of a truncated triangle which partly surrounds an oscillating proof mass.

