Vibrating micro-mechanical sensor of angular velocity

WO 2010/100334 PCT/FI2010/050160 1

Vibrating Micro-mechanical Sensor of Angular Velocity

Field of the Invention 5 The invention relates to measuring devices used for the measuring of angular velocity, and, more precisely, to vibrating micro-mechanical sensors of angular velocity. The object of the invention is to provide an improved sensor structure enabling reliable measuring with good efficiency 10 particularly in small vibrating micro-mechanical angular velocity sensor solutions .

Background of the Invention 15 Measuring based on a vibrating sensor of angular velocity has proved to be a method of measuring angular velocity having a simple concept and being reliable. In a vibrating sensor of angular velocity, a certain known primary motion is produced and it is maintained in the sensor. The motion desired to be 20 measured with the sensor is then detected as a deviation of the primary motion.

Central features required of sensors of angular velocity are resistance to shaking and impact. Particularly in demanding 25 applications, such as e.g. driving control systems in the car industry, these requirements are extremely tight. Even a sharp blow, like for instance an external impact caused by a stone, or the vibration caused by a car stereo should not influence the output of the sensor of angular velocity. 30

The principle of operation of vibrating sensors of angular velocity most often used is the so called tuning fork principle. In the tuning fork principle the primary motion is a vibration of two linear resonators vibrating in opposite WO 2010/100334 PCT/FI2010/050160 2 phase on a common axis. An external angular velocity affecting the sensor in a direction perpendicular to the direction of motion of the resonators causes Coriolis forces influencing the masses in opposite directions. 5 A Coriolis force proportional to the angular velocity is detected either directly from the masses, or the masses are connected on the same rotational axis, whereby the detection motion is angular vibration in the direction of the angular 10 velocity axis. The angular vibration to be detected is, however, susceptible to external mechanical interference.

Inevitably, from impact events and vibrations, instances of angular acceleration, due to vibrations of the material and 15 the substructure, are generated also to the detection axis of the sensor of angular velocity. Then the motion of the detection resonator is disturbed and deviations are caused to the output signal of the sensor of angular velocity, particularly when the frequency of the interference is close 20 to the operating frequency of the sensor.

Several sensor solutions of prior art have been presented in order to compensate for interference signals. Such a sensor has often been made by using so called differential 25 detection, whereby a sensor structure can be achieved, which is considerably less insensitive to external mechanical interference. One such prior art sensor solution, for example, is described in the US patent publication US 6,705,164, wherein two seismic masses, positioned alongside 30 each other, are linearly vibrating in opposite phases in the surface plane and in the same direction. Thus, the detection resonator axis is common for both masses and perpendicular to the primary motion. WO 2010/100334 PCT/FI2O10/050160 3

In differential detection, a common axis of motion for the centers of gravity of the detection resonators provides optimal insensitivity to external mechanical disturbance. Differential detection with two masses cancels external linear accelerations and, in the special case of a common detection axis, also instances of angular acceleration, since the sensitivity to angular acceleration of a traditional tuning fork gyro is proportional to the distance between the detection resonators axes.

Thus, this implementation of a sensor of angular velocity according to the so called reversed tuning fork principle operates significantly more reliably in shaking conditions in comparison with e.g. a traditional tuning fork. However, the greatest weakness of the reversed tuning fork principle is the primary motion's susceptibility to external disturbances.

In the structure according to the US patent publication US 6,705,164 mentioned above, the coupled linear resonators are more easily mobile in a common phase than in opposite phase. Then, the linear acceleration along the primary axis can fairly easily disturb the operation of the sensor, since the masses are physically displaced, although the differential detection of them to a major extent mitigates the thereby caused signal. A better solution than the differential detection for compensation of mechanical disturbances is the so called dual differential detection. Such a prior art sensor solution is i.a. described in the US patent publication US 6,122,961, wherein, in Figure 3, a dual differential tuning fork structure is presented, which structure also includes the reverse tuning fork operating principle with parallel masses presented above. WO 2010/100334 PCT/FI2010/050160

In the US patent publication US 6,122,961, four masses are coupled together into a-dual differential tuning fork structure, in which two pairs of differential masses according to the tuning fork are vibrating in opposite phase in parallel. This prior art structure thus contains two opposite phase reversed tuning forks.

The dual differential tuning fork is, in fact, the most reliable angular velocity sensor structure based on linear motion in one plane. Its greatest weakness is, however, an extremely complicated and bulky spring structure. The excitation structures are also difficult to design and they also take a lot of space.

Another significant challenge in designing a good sensor of angular velocity is the capacitive crosstalk of electrostatic drive, particularly into Coriolis detection. The drive signal of the primary motion is in phase with the speed of the masses, and then the crosstalk signal is most often observed precisely in phase with the Coriolis signal. This causes a disturbance in the value of the zero point of the sensor dependent on the amplitude of the drive signal, which causes an error dependent on i. a. the temperature. A conventional solution to this problem is the so called carrier detection. In carrier detection an AC voltage, i.e. a carrier wave, is applied across a capacitance to be measured. In this arrangement, the variable capacitance is made to modulate the amplitude of the output signal of a preamplifier, and a voltage dependent on the capacitance is obtained by demodulating with the carrier. Then the interference signal caused by capacitive crosstalk will be modulated away from the signal band at the carrier frequency. WO 2010/100334 PC Τ/ΓΙ2010/050160

However, carrier detection complicates the already quite complicated electronics of the sensor of angular velocity, which then contributes to increasing cost and size of the 5 electronics and impairs its reliability. It is actually worthwhile to design the capacitive sensor element in such a way, that crosstalk of the drive signal caused by stray capacitances will cancel out as thoroughly as possible in differential Coriolis detection. 10

The objective of the invention is, indeed, to achieve a structure of a vibrating sensor of angular velocity suitable for a small size, and being resistant to interference, by means of which angular velocity perpendicular to the surface 15 plane can be measured in a reliable manner.

Summary of the Invention

The objective of the invention is to provide such an improved 20 vibrating sensor of angular velocity, which enables measuring, reliably and with good performance, of angular velocity perpendicular to the surface plane, particularly in solutions of small vibrating sensors of angular velocity, and which, in comparison with prior art solutions with two 25 masses, is remarkably much less sensitive to mechanical interference.

According to the invention, a vibrating micro-mechanical sensor of angular velocity is provided, which comprises at 30 least two seismic mass structures such, that the sensor of angular velocity additionally comprises excitation structures and coupling seesaw type springs in such a way, that said at least two seismic mass structures are positioned apart and are supported to the excitation structures by means of WO 2010/100334 PCT/FI2010/050160 6 springs such, that said excitation structures are supported to anchoring points at least at one of their ends by means of the coupling seesaw type springs. 5 Preferably, said seesaw type springs are arranged such, that the stiff support structure of the spring is allowed to turn in the surface plane about a fixed axis. Preferably, said seesaw type springs are arranged such, that the springs force the excitation structures comprising said at least two 10 seismic mass structures into vibration in the surface plane in opposite phases. Preferably, the paths of motion of the vibration in opposite phases of said excitation structures form two parallel arcs in opposite directions. 15 Preferably, the sensor of angular velocity further comprises excitation comb structures positioned between the excitation structures comprising said at least two seismic mass structures. Preferably, said excitation comb structures are supported to a centrally located anchoring structure. 20

Preferably, the sensor of angular velocity further comprises quadrature motion compensating comb structures positioned between the excitation structures comprising said at least two seismic mass structures. Preferably, the sensor of 25 angular velocity further comprises detection comb structures, which detection comb structures are adapted to differential detection of the primary motion. Preferably, the sensor of angular velocity further comprises Coriolis detection comb structures, which detection comb structures are adapted to 30 dual differential detection of the Coriolis motion caused by angular velocity. WO 2010/100334 PCT/FI2010/050160

Brief Description of the Drawings

Below, the invention and preferable embodiments thereof are 5 described in detail with exemplifying reference to the accompanying figures f of which:

Figure 1 shows a diagram of the functional structure of a vibrating micro-mechanical sensor of angular velocity 10 according to the invention,

Figure 2 shows a diagram of an alternative functional structure of a vibrating micro-mechanical sensor of angular velocity according to the invention,

Figure 3 shows a diagram of a second alternative functional 15 structure of a vibrating micro-mechanical sensor of angular velocity according to the invention.

Figure 4 shows a diagram of a third alternative functional structure of a vibrating micro-mechanical sensor of angular velocity according to the invention. 20 Figure 5 shows an example of an embodiment without a secondary coupling in detail.

Detailed Description of the Invention 25

Figure 1 shows a diagram of the functional structure of a vibrating micro-mechanical sensor of angular velocity according to the invention. The depicted vibrating micromechanical sensor of angular velocity according to the 30 invention comprises two mass structures 1, 2 positioned apart, which mass structures 1, 2 are supported to excitation structures 3, 4 by means of springs 27—30. Said excitation structures 3, 4 are supported by means of coupling seesaw WO 2010/100334 PCT/FI2010/050160 8 type springs 6, 7 to anchoring points 8—11 of a frame 5 bordering the sensor.

The vibrating micro-mechanical sensor of angular velocity 5 according to the invention further comprises capacitive comb structures 23—26 supported to the seismic masses 1, 2, and excitation comb structures 12, 13 connected to the excitation structures 3, 4. Said excitation comb structures 12, 13 are positioned between the excitation structures 3, 4 comprising 10 the mass structures 1, 2, and said excitation comb structures 12, 13 are supported to a centrally located anchoring structure 14.

The vibrating micro-mechanical sensor of angular velocity 15 according to the invention further comprises capacitive excitation motion detecting comb structures 17, 18 supported to anchoring points 21, 22, and quadrature motion compensation comb structures 31, 32. 20 In the vibrating micro-mechanical sensor of angular velocity according to the invention, the primary motion is excited electrostatically by the opposite excitation comb structures 12, 13 by means of a common mode signal, and it is differentially detected by the detection comb structures. 25

The vibrating micro-mechanical sensor of angular velocity according to the invention comprises two seismic mass structures 1, 2 positioned apart, which mass structures 1, 2 are suspended by means of the excitation structures 3, 4 and 30 the coupling springs 6, 7 to anchoring points 8—11 fastened to the cover and/or bottom of the sensor.

The coupling springs 6, 7 according to the invention are designed such, that the stiff support structure is allowed to WO 2010/100334 PCT/FI2010/050160 9 turn in the surface plane about a fixed axis. Thus, the primary motion suspension 6, 7 forces the excitations 3, 4 of the seismic masses 1, 2 into vibration in opposite phases in the surface plane. The motion paths of the excitations 3, 4 5 form two parallel arcs in opposite directions.

In the vibrating micro-mechanical sensor of angular velocity according to the invention, the seismic masses 1, 2 are suspended to the excitations 3, 4 such, that the suspension 10 27—30 enables a deviation in the surface plane from the primary motion of the mass, caused by a Coriolis force. The deviation can be detected by the detection comb structures 15—18, which detect the deviation in the surface plane in opposite directions of the masses 1, 2, in a direction 15 perpendicular to the excitation direction.

Figure 2 shows a diagram of an alternative functional structure of the vibrating micro-mechanical sensor of angular velocity according to the invention. The depicted alternative 20 vibrating micro-mechanical sensor of angular velocity according to the invention comprises two mass structures positioned apart, which mass structures are supported to excitation structures by means of springs. Said excitation structures are supported to the sensor7 s anchoring points by 25 means of coupling seesaw type springs. The alternative vibrating micro-mechanical sensor of angular velocity according to the invention comprises capacitive comb structures supported to the excitation structures and excitation comb structures connected to the excitation 30 structures. Said excitation comb structures are positioned between the excitation structures comprising the mass structures, and said excitation comb structures are supported to a centrally located anchoring structure. The alternative vibrating micro-mechanical sensor of angular velocity WO 2010/100334 PCT/FI2010/050160 10 according to the invention comprises capacitive excitation motion detection comb structures and quadrature motion compensation comb structures. 5 In the alternative vibrating micro-mechanical sensor of angular velocity according to the invention, in addition to the coupling springs, the excitation structures are supported to the sensor's anchoring points by means of primary motion dimensioning springs, 10

In the alternative vibrating micro-mechanical sensor of angular velocity according to the invention, the suspension of the excitation structures can be strengthened and the resonance frequency and the radius of curvature of the 15 primary motion can be adjusted by means of the separate primary motion dimensioning springs.

Figure 3 shows a diagram of a second alternative functional structure of a vibrating micro-mechanical sensor of angular 20 velocity according to the invention. The depicted second alternative vibrating micro-mechanical sensor of angular velocity according to the invention comprises two mass structures positioned apart, which mass structures are supported to excitation structures by means of springs. Said 25 excitation structures are supported to the sensor's anchoring points by means of coupling seesaw type springs. The second alternative vibrating micro-mechanical sensor of angular velocity according to the invention comprises capacitive comb structures supported to the excitation structures and 30 excitation comb structures connected to the excitation structures. Said excitation comb structures are positioned between the excitation structures comprising the mass structures, and said excitation comb structures are supported to a centrally located anchoring structure. The second WO 2010/100334 PCT/FI2010/050160 11 alternative vibrating micro-mechanical sensor of angular velocity according to the invention comprises capacitive excitation motion detection comb structures and quadrature motion compensation comb structures. 5

In the second alternative vibrating micro-mechanical sensor of angular velocity according to the invention, in addition to the coupling springs, the excitation structures are supported to the sensor's anchoring points by means of 10 primary motion dimensioning springs, and also, by means of second primary motion dimensioning springs, to the frame 5 bordering the sensor component.

In the second alternative vibrating micro-mechanical sensor 15 of angular velocity according to the invention, the suspension of the excitation structures can be strengthened and the resonance frequency and the radius of curvature of the primary motion can be adjusted by means of the separate primary motion dimensioning springs. 20

In the second alternative vibrating micro-mechanical sensor of angular velocity according to the invention, the excitations are suspended, in addition to the coupling springs, at all four corners by means of the primary motion 2 5 dimensioning springs, which increase the radius of curvature of the primary motion to become almost infinite and thus limit its motion to become essentially linear in the surface plane . 30 Figure 4 shows a diagram of a third alternative functional structure of a vibrating micro-mechanical sensor of angular velocity according to the invention. The depicted third alternative vibrating micro-mechanical sensor of angular velocity according to the invention comprises two mass WO 2010/100334 PCT/FI2010/050160 12 structures positioned apart, which mass structures are supported to excitation structures by means of springs. Said excitation structures are supported to the sensor's anchoring points by means of coupling seesaw type springs. The third 5 alternative vibrating micro-mechanical sensor of angular velocity according to the invention comprises capacitive comb structures supported to the excitation structures and excitation comb structures connected .to the excitation structures. Said excitation comb structures are positioned 10 between the excitation structures comprising the mass structures, and said excitation comb structures are supported to a centrally located anchoring structure. The third alternative vibrating micro-mechanical sensor of angular velocity according to the invention comprises capacitive 15 excitation motion detection comb structures and quadrature motion compensation comb structures.

In the third alternative vibrating micro-mechanical sensor of angular velocity according to the invention, in addition to 20 the coupling springs, the excitation structures are supported to the sensor's anchoring points by means of primary motion dimensioning springs and also to the frame of the sensor component at anchoring points by means of second primary motion dimensioning springs. In the third alternative 25 vibrating micro-mechanical sensor of angular velocity according to the invention, the suspension of the excitation structures can be strengthened and the resonance frequency and the radius of curvature of the primary motion can be adjusted by means of the separate primary motion dimensioning 30 springs.

In the third alternative vibrating micro-mechanical sensor of angular velocity according to the invention, the excitations are suspended, in addition to the coupling springs, at all WO 2010/100334 PCT/FI2010/050160 13 four corners by means of the primary motion dimensioning springs, which increase the radius of curvature of the primary motion to become almost infinite and thus limit its motion to become essentially linear in the surface plane. 5

In the third alternative vibrating micro-mechanical sensor of angular velocity according to the invention, the dual differential detection comb structures are further supported to the excitation structures by means of spring structures. 10

In the solution according to the invention, a primary motion excitation structure with one end is positioned between the masses. In the solution according to the invention, further, the Coriolis force detection structures are differential and 15 they are located symmetrically on both sides of the sensor component far away from the excitation structures and they are fastened to the frame of the sensor component on its both sides, as close together as possible. Additionally, the quadrature signal compensation structures are positioned 20 between the excitation structure and he detection structures as symmetrically as possible. Thus, there will be as little as possible of excitation signal crosstalk into the detection, caused by stray capacitances, and additionally it will be cancelled out in differential listening. 25

According to an embodiment the sensor structure comprises a common-mode drive combs structure attached to a drive structure between masses. According to an embodiment of the invention the sensor structure comprises a symmetric double- 30 differential sense combs within masses. According to an embodiment of the invention According to an embodiment of the invention the excitation structure is implemented by a frame as an excitation frame structure. According to such an embodiment the structure comprises a closed frame structure. WO 2010/100334 PCT/FI2010/050160 14

In addition to the described exemplifying structures, within the scope of the invention a multitude of modifications can be presented of the sensor of angular velocity with two axes 5 according to the invention. onosuzon nnuza , crnxan rwzn οϊό pnow pnszn irn nr “|»ob ,ρνιο ηχΰπ ηοοοπο nazrno noizzmoo np’ioo .□όοεζοπ rwoo mpnon ρηυ1? οχηηο οιηπη Psz

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