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Patent Issued for Vibrating Micromechanical Sensor of Angular Velocity

February 12, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Klemetti, Petri (Klaukkala, FI); Nera, Kaisa (Helsinki, FI); Lipsanen, Antti (Espoo, FI); Blomqvist, Anssi (Helsinki, FI); Torkkeli, Altti (Tuusula, FI), filed on December 16, 2011, was published online on January 28, 2014.

The patent's assignee for patent number 8635909 is Murata Electronics Oy (Vantaa, FI).

News editors obtained the following quote from the background information supplied by the inventors: "In measuring angular velocity, the principle of the method of measuring based on a vibrating sensor of angular velocity has proved to be simple and reliable. In a vibrating sensor of angular velocity, a certain known primary motion is induced and maintained in the sensor. The desired motion to be measured by means of the sensor is then detected as a deviation of the primary motion.

"An external angular velocity in a direction perpendicular to the resonators' direction of motion acting on the sensor induces a Coriolis force in the seismic mass in a direction perpendicular to its direction of motion. The Coriolis force, proportional to the angular velocity, is detected, for example capacitively, in the vibration of the mass.

"One of the most significant problems in micromechanical vibrating sensors of angular velocity is the so called quadrature signal, which is caused by poor dimensional precision in the structures. In resonators manufactured using the means of micromechanics, there may be found tolerance errors in the perpendicularity of the directions of motion, which in the detection of the sensor of angular velocity cause a signal, called the quadrature signal, of a magnitude, at worst, hundreds of times larger than the angular velocity signal corresponding to the maximum value of the output scale.

"The angular velocity signal to be measured, being proportional to the speed of the mass, is luckily phase-shifted by 90 degrees in relation to the quadrature signal, whereby the quadrature signal disappears in an ideal demodulation. However, being significantly larger than the signal to be measured, it restricts the dynamics of the signal. Another big disadvantage of the quadrature signal is, that it, if left uncompensated for, significantly degrades the stability of the zero point of the sensor, due to phase shifts in the electronic signals as, for example, the temperature changes.

"In the sensor, the quadrature signal can be compensated for by using electric forces. One of the known techniques is i.a. feed-forward compensation, in which a force modulated by the detected primary motion is fed back into the detecting resonator at a phase opposite to the quadrature signal. Alternative ways of electrical compensation include, for example, straightening of the direction of motion by a static electric force or by a force generated by a static entity modulated by the motion, which force compensates for the quadrature signal caused by a residual of the spring force.

"Compensation by means of electric forces constitutes a challenge to the sensor's electronics. What is required is either accurate phase control or, possibly, large voltages and separate structures within the sensor.

"Thus, the object of the invention is to provide a structure of a vibrating sensor of angular velocity, in which the compensation for the quadrature signal is implemented directly by mechanical design, without electric forces.

"Referring to prior art, the Finnish patent publication FI-116543B1 describes a sensor of angular velocity according to prior art, where the seismic masses are connected to support areas by springs and/or stiff auxiliary structures, which give the masses a degree of freedom in relation to an axis of rotation perpendicular to the plane of the disk they are forming, and to at least one axis of rotation extending in the direction of the plane of the disk.

"Further, referring to prior art, the Finnish patent publication FI-116544B1 describes a sensor of angular velocity according to prior art, where at least one pair of electrodes is formed in association with the edge of the seismic mass, which pair of electrodes forms two capacitances with the surface of the mass, so that, as a function of the angle of rotation of the mass's primary motion, one capacitance of the pair of electrodes increases and the other capacitance of the pair of electrodes decreases."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "The objective of the invention is to provide such an improved vibrating sensor of angular velocity, which enables reliable measuring with a good performance, particularly in solutions with a small vibrating sensor of angular velocity, and in which the compensation for the quadrature signal is implemented by mechanical design without electric compensation, or, alternatively, in combination with the electric compensation methods mentioned above.

"According to a first aspect of the invention, a vibrating micromechanical sensor of angular velocity is provided, which comprises at least one seismic mass and, associated with the mass, a moving electrode, which mass possesses a primary motion, which is to be activated, and, in addition to the primary motion, at least one degree of freedom in relation to a detection axis, or detection axes, essentially perpendicular to the primary motion, and which mass, or which masses, is/are supported to the frame of the sensor component by means of a spring structure such, that the spring structure is asymmetric such, that the coupling, conveyed by the spring, from one mode of motion to another cancels or alleviates the coupling caused by non-ideality due to skewness of the springs or their support.

"Preferably, one corner of the spring structure is etched off. Alternatively, one or more compensation groove is etched into the spring structure. Further, alternatively, one or more compensation cavity is etched into the spring structure. Further, alternatively, one or more compensation groove or compensation cavity is etched into at least one attachment spot for the spring structure. Further, preferably, the compensation grooves or the compensation cavities are suitably dimensioned such, that they effectively straighten the end portion of a skewed spring.

"Alternatively, one edge of the spring structure is serrated. Alternatively, both edges of the spring structure are serrated. Further, preferably, the serration is suitably dimensioned to be one-sided or asymmetric such, that the serration twists the bending axis of the spring.

"Preferably, the spring structure is designed to be asymmetric such, that the coupling from one mode of motion to another, conveyed by the spring, cancels or alleviates the coupling caused by non-ideality due to an inclination relative to the perpendicular to the disk of the groove of the DRIE etching process.

"According to a second aspect of the invention, a method is provided for manufacturing, by means of micromechanical disk structures, a vibrating micromechanical sensor of angular velocity comprising at least one seismic mass and, in association with the mass, a moving electrode, which mass possesses a primary motion to be activated and, in addition to the primary motion, at least one degree of freedom in relation to a detection axis, or detection axes, essentially perpendicular to the primary motion, and which mass, or which masses, is/are supported to the frame of the sensor component by means of a spring structure such, that the spring structure of the sensor of angular velocity is made asymmetric by etching.

"Preferably, the etching mask is designed such, that it compensates for non-idealities occurring over the surface of the disk, caused by the manufacturing process. Preferably the DRIE etching technique (DRIE, Deep Reactive Ion Etching) is used in the manufacturing. Preferably, in the manufacturing, non-idealities of the DRIE etching process are utilized, such as the ARDE effect (ARDE, Aspect Ratio Dependent Etch rate). Preferably, a two-stage DRIE etching process is utilized in the manufacturing, by means of which the depth of the etched groove or cavity can be suitably dimensioned."

For additional information on this patent, see: Klemetti, Petri; Nera, Kaisa; Lipsanen, Antti; Blomqvist, Anssi; Torkkeli, Altti. Vibrating Micromechanical Sensor of Angular Velocity. U.S. Patent Number 8635909, filed December 16, 2011, and published online on January 28, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=96&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=4753&f=G&l=50&co1=AND&d=PTXT&s1=20140128.PD.&OS=ISD/20140128&RS=ISD/20140128

Keywords for this news article include: Murata Electronics Oy.

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Source: Electronics Newsweekly


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