Abstract:
An ion discharge gyroscope measures rotational motion and linear acceleration by generating symmetrical ion jet streams and measuring respective amounts of the jet streams impinging on detectors located so as to intercept the ion jet streams. The ion jet streams will be diverted by operation of the Coriolis effect and the differences in the amount of each ion jet stream impinging on the detectors is an indication of rotational motion and linear acceleration. In one embodiment, the ion jet streams are heated and the respective temperatures of the detectors are measured. In another embodiment, the amounts of current flowing through each detector, as contributed by the ion jet streams, are measured and used to determine rotation and acceleration.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    Priority of U.S. Provisional Patent Application Ser. No. 61/223,457 for “Ion Gyroscope,” filed Jul. 7, 2009, is claimed. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    N/A 
       BACKGROUND OF THE INVENTION 
       [0003]    A gyroscope is a sensing device that detects rotational motion, i.e., angular velocity. Typical applications include, for example, navigation devices, camera image stabilization mechanisms and gaming equipment. There are different types of gyroscopes including optical (fiber gyro), flying wheel and MEMS (micro-electrical-mechanical-system). 
         [0004]    In the consumer electronics market for mobile phones, GPS devices, etc., small size, low cost and robustness are critical to mass deployment. Currently, the MEMS-based gyroscope is gradually finding its way to this market. These gyroscopes are based on the Coriolis acceleration which is proportional to the velocity           of a vibrating structure and the external rotation rate           such that the Coriolis acceleration          =2         ×         . 
         [0005]    A known MEMS-based vibration-mode gyroscope uses a beam structure and a capacitive sensing mechanism. This approach, however, is subject to inaccuracy induced by mechanical shock and suffers from other reliability issues. In addition, such sensors require a complicated MEMS manufacturing process and a relatively large sensing area. As would be expected, therefore, the manufacturing costs are higher when compared to other MEMS-based devices, such as an accelerometer, a microphone, etc. These issues have prevented a MEMS-based gyroscope from being widely deployed in consumer electronics. 
         [0006]    convective gyroscope is known and its design involves a micro pump that generates a hot fluid jet stream. This hot jet stream will change its direction in the presence of rotational motion. The micro pump is typically actuated by a piezoelectric lead zirconate titanate (PZT) diaphragm but is difficult to manufacture in a MEMS process. 
         [0007]    What is needed is a MEMS-based gyroscope that is accurate, has high reliability and that is economical to manufacture. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    An ion discharge gyroscope provides accurate measurement of rotational motion and linear acceleration by generating symmetrical ion jet streams and measuring respective amounts of the jet streams impinging on detectors located to intercept the respective ion jet streams. The ion jet streams will be diverted by operation of the Coriolis effect and the differences in the amount of each ion jet stream impinging on the detectors is an indication of rotational motion and linear acceleration. In one embodiment, the ion jet streams are heated and the respective temperatures of the detectors are measured. In another embodiment, the amounts of current flowing through each detector, as contributed by the ion jet stream, are measured and used to determine rotation and acceleration. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    Various aspects of at least one embodiment of the present invention are discussed below with reference to the accompanying figures. It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components may be included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. For purposes of clarity, however, not every component may be labeled in every drawing. These figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the invention. In the figures: 
           [0010]      FIG. 1  is a representation of an orientation and general shape of the sensors described herein; 
           [0011]      FIGS. 2A-2C  are schematic representations of an ion gyroscope according to one embodiment of the present invention; 
           [0012]      FIGS. 3A-3D  are schematic representations of an ion gyroscope according to a second embodiment of the present invention; 
           [0013]      FIG. 4  is a measurement circuit for use with either of the first and second embodiments of the present invention shown in  FIGS. 2 and 3 ; 
           [0014]      FIGS. 5A-5D  are schematic representations of an ion gyroscope according to a third embodiment of the present invention; 
           [0015]      FIG. 6  is a measurement circuit for use in conjunction with the third embodiment of the present invention; 
           [0016]      FIG. 7  is an alternate version of the third embodiment of the present invention; 
           [0017]      FIG. 8  is another alternate version of the third embodiment of the present invention; 
           [0018]      FIG. 9  is an alternate implementation of the first embodiment of the present invention; and 
           [0019]      FIG. 10  is a flowchart of methods in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    U.S. Provisional Patent Application Ser. No. 61/223,457 for “Ion Gyroscope,” filed Jul. 7, 2009, is incorporated by reference herein in its entirety and for all purposes. 
         [0021]    One or more embodiments of the present invention are directed to an ion discharge gyroscope that provides accurate measurement of rotational motion in addition to being robust enough to withstand the forces of most consumer product implementations and in a structure that is relatively easy to manufacture. 
         [0022]    As an overview, and referring now to  FIG. 1 , a sensor  100 , embodiments of which will be described in more detail below, is generally formed on a rectangular substrate  102  fabricated out of silicon or other similar material. Typically, the substrate is on the order of 1-2 mm on a side. A cavity  104  is etched in the substrate  102  in order to provide a working space for the gyroscope movement. Generally, a longitudinal direction L will be defined and referenced throughout the present specification with the longitudinal direction L aligned with an X axis that is co-planar and perpendicular to a Y axis. For ease of explanation below, a Z axis is defined as being orthogonal to the plane defined by the X, Y axes. 
         [0023]    In one embodiment of an ion gyroscope  200 , as shown in  FIGS. 2A-2C , a substrate  102  is provided with a cavity  104  within which is disposed an anode  202  having a sharp anode tip  203 . Alternatively, there may be more than one sharp anode tip provided on the anode, however, a single anode tip makes it easier to ionize a gas as will be discussed below. A cathode  204  is disposed in the cavity  104  and opposite the sharp tip  203 . A first set  207 - 1  of thermocouples including a positive thermocouple (TCP)  208  and a negative thermocouple (TCM)  210  are provided within the cavity  104  and arranged such that, generally, the cathode  204  is disposed between the anode  202  and the positive and negative thermocouples  208 ,  210 . A heater  206  is provided in the cavity  104  between the anode and cathode. The positive thermocouple  208  has a corresponding output TCP 1  and the negative thermocouple  210  has a corresponding output TCM 1  that are, respectively, coupled to the inputs of a differentiated amplified  402 - 1 , as shown in  FIG. 4 . 
         [0024]    A gas, for example, Nitrogen, Neon or Argon, is provided in the cavity  104  which is sealed to keep the gas in place. The provisioning of the gas and the sealing of the cavity  104  are done in accordance with practices known to those of ordinary skill in the art. 
         [0025]    Referring now to  FIG. 2B , in operation, a high DC voltage source  220  is coupled to the anode  202  and the cathode  204 . The voltage level of the DC voltage source  220  depends on the gas is used in the cavity  104 . For Neon and Argon, the voltage is in the range of 10-20 volts, however, 
         [0026]    Nitrogen requires around 300 volts. The voltage requirement increases as the distance from the anode to either the cathode or ground, as discussed below, increases. There are advantages to using a gas, therefore, that has a lower ionization voltage. When turned on, the gas in the cavity  104  is ionized by the high DC voltage source  220  to create an ion cloud  222  at the sharp anode tip  203 . An electric field created between the anode  202  and the cathode  204  drives the ion cloud  222  towards the cathode  204  thereby forming an ion jet stream  224 . 
         [0027]    The heater  206  is placed in the path of the ion jet stream  224 , so as to heat the ion jet stream  224  before it reaches the temperature sensing positive and negative thermocouples  208 ,  210 . The heater  206  is heated by passing current through its structure and, in one embodiment, is heated to about 100° K above ambient temperature. It should be noted that the heater  206  is positioned so as to heat the ion jet stream  224  without blocking the ion jet stream  224  from reaching the thermocouples  208 ,  210 . A respective temperature of the ion jet stream  224  impinging on each of the thermocouples  208 ,  210  is represented by the sensed values TCP 1 , TCM 1 . 
         [0028]    The heater  206  is fabricated using standard CMOS layers, such as Polysilicon or metal. A release etch will remove silicon underneath the heater  206  and the release etch can be the same process step that is used to make the cavity  104 . The suspended structure of the heater  206 , discharge tip  203  and thermocouples  207  are thin in nature, generally a few microns (μm). The heater  206  will not block the ion jet stream  224  flow in the lateral direction. 
         [0029]    At rest, i.e., when the device  200  is neither spinning nor linearly moving, the positive and negative thermocouples  208 ,  210  should sense a same temperature. Thus, a difference between their respective signals TCP 1 , TCM 1  is zero as the ion jet stream  224  is traveling in a straight direction, in this case, along the X axis, and impinging equally on the thermocouples. Thus, the output signal ROTATIONØ, shown in  FIG. 4 , would be zero. 
         [0030]    In a situation where the device  200  is rotating, as shown in  FIG. 2C , i.e., rotating about the Z axis which, in  FIG. 2C , is coming up out of the drawing, the ion jet stream  224  will be skewed io toward either the positive thermocouple  208  or the negative thermocouple  210 . As a result, there will be a temperature difference between the positive and negative thermocouples  208 ,  210  resulting in a difference between the respective output signals TCP 1 , TCM 1  and the value ROTATIONØ will be greater or less than zero, depending upon the direction of spin. 
         [0031]    The gyroscope  200  shown in  FIGS. 2A-2C , however, is subject to interference in the output signal ROTATIONØ due to linear acceleration. That is, when the device  200  is accelerating along a direction that is, for example, perpendicular to the gas stream direction, the ion jet stream  224  will be skewed in the opposite direction. Such a skewing, however, will create an error in the reading that will be difficult to distinguish from the effects of rotation. 
         [0032]    A symmetric ion gyroscope  300 , as shown in  FIGS. 3A-3D , provides compensation for linear acceleration. 
         [0033]    Referring now to  FIG. 3A , the symmetric gyroscope  300  comprises a substrate  102  with a cavity  104  similar to the embodiment described above. A symmetric anode  302  is positioned in the cavity  104  and includes sharp tips  203  disposed on each side of the symmetric anode  302 . First and second cathodes  204 - 1 ,  204 - 2  are disposed within the cavity  104  along with first and second heaters  206 - 1 ,  206 - 2  positioned between the symmetric anode  302  and the first and second cathodes  204 - 1 ,  204 - 2 , respectively. A first pair  207 - 1  of positive and negative thermocouples  208 - 1 ,  210 - 1  that provide outputs TCP 1  and TCM 1  along with a second pair  207 - 2  of positive and negative thermocouples  208 - 2 ,  210 - 2  that provide signals TCP 2 , TCM 1  are disposed in the cavity  104 . One of ordinary skill in the art will understand that the symmetric gyroscope  300  represents “mirror image” versions of the gyroscope  200  described above. 
         [0034]    Referring now to  FIG. 4 , a measurement circuit  400  consists of first and second differential amplifiers  402 - 1 ,  402 - 2 , that receive, respectively, (TCP 1 , TCM 1 ) and (TCP 2 , TCM 2 ) the outputs of which are respectively coupled to the non-inverting and inverting inputs of a third differential amplifier  402 - 3  to output a difference therebetween as a ROTATION 1  signal. In addition, the respective outputs of the first and second differential amplifiers  402 - 1 ,  402 - 2  are input to a summer circuit  404  that adds the signals together to provide an indication of linear acceleration. 
         [0035]    In operation, referring now to  FIG. 3B , first and second high DC voltage power sources  220 - 1 ,  220 - 2 , are coupled to the symmetric anode  302  and the first and second cathodes  204 - 1 ,  204 - 2 , respectively. 
         [0036]    When the first and second voltage sources  220 - 1 ,  220 - 2 , and the heaters  206 - 1 ,  206 - 2 , are turned on, and the symmetric gyroscope  300 , is at rest, the ion jet streams  224 - 1 ,  224 - 2  strike the pairs  207 - 1 ,  207 - 2  of positive and negative thermocouples  208 ,  210  equally and the differences between all outputs TCP 1 , TCM 1 , and TCP 2 , TCM 2  are zero. 
         [0037]    When the symmetric gyroscope  300  is rotated, as shown in  FIG. 3C , the first and second ion jet streams  224 - 1 ,  224 - 2  will be deflected in opposite directions. Accordingly, there will be a difference between the first and second pairs of thermocouples  207 - 1 ,  207 - 2  output signals TCP 1 , TCM 1  and TCP 2 , TCM 2 . Such a difference, as will be calculated as described below, can be used to identify an amount of rotational motion. 
         [0038]    As show in  FIG. 3D , when the symmetric gyroscope  300  is linearly accelerated in, for example, the Y direction, the first and second jet streams  224 - 1 ,  224 - 2  will be deflected in the opposite direction. An imbalance in the temperature sensed as between the pairs of positive and negative thermocouples  207 - 1 ,  207 - 2  will indicate an amount of linear acceleration. 
         [0039]    Thus, when the symmetric gyroscope  300  is rotating, the signals from the first and second pairs  207 - 1 ,  207 - 2  of positive and negative thermocouples will have opposite polarities. The ROTATION 1  signal output from the differential amplifier  402 - 3  will indicate a magnitude of rotation in addition to a direction. 
         [0040]    The amount of linear acceleration is provided by the summer  404  which sums, i.e., averages, the differences between the pairs  207 - 1 ,  207 - 2 , of positive and negative thermocouples  208 ,  210 , while also indicating a direction of acceleration. 
         [0041]    In a third embodiment of the present invention, an ion gyroscope  500 , as shown in  FIGS. 5A-5D , uses current mode sensing rather than thermo sensing. Accordingly, as shown in  FIG. 5A , the current mode gyroscope  500  includes a substrate  102  with a cavity  104  as described above. In addition, a symmetric anode  302  is positioned within the cavity  104 . A first ground electrode  501 - 1  is provided within the cavity  104  and consists of a first upper portion  502 - 1  and a first lower portion  504 - 1 . A second ground electrode  501 - 2  is split into respective upper and lower portions  502 - 2 ,  504 - 2 , respectively. One will understand that these ground electrodes can also be considered as being cathodes. 
         [0042]    As shown in  FIG. 5B , a first DC voltage sources  220 - 1  and a first current meter  506 - 1  are s coupled between the anode  302  and the first lower portion  504 - 1 . The first current meter  506 - 1  provides a signal Im 1  indicating the amount of current flowing in that leg of the circuit. A second DC voltage source  220 - 2  and a second current meter  506 - 2  are coupled between the anode  302  and the second lower portion  504 - 2 . The second current meter  506 - 2  provides a signal Im 2  indicating the amount of current flowing in that leg of the circuit. A third DC voltage source  220 - 3  and a third current meter  506 - 3  are coupled between the anode  302  and the first upper portion  502 - 1  of the first ground electrode. The third current meter  506 - 3  provides a signal Ip 1  indicating the amount of current flowing in that leg of the circuit. A fourth DC voltage source  220 - 4  and a fourth current meter  506 - 4  are coupled between the anode  302  and the second upper portion  502 - 2  of the second ground electrode  502 - 2 . The fourth current meter  506 - 4  provides a signal Ip 2  indicating the is amount of current flowing in that leg of the circuit. 
         [0043]    Similar to the first and second embodiments, when the power supplies are turned on, an ion cloud and ion jet stream will be formed and will flow from the anode toward the ground electrodes. As the ion jet streams  224 - 1 ,  224 - 2  actually carry current, in the case of zero deflection, i.e., at a standstill, the currents will be equally split between the upper and lower ground electrodes in each of the first and second pairs  501 - 1 ,  501 - 2  and reflected in the current measurements Ip 1 , Im 1  and Ip 2 , Im 2 . In the presence of deflection, either due to linear acceleration or rotation, the current will not be equal. The indication of motion and its magnitude will be reflected in the output signals. 
         [0044]    A measurement circuit  600 , as shown in  FIG. 6 , determines the amount of rotation or linear acceleration and includes first and second current difference devices  602 - 1 ,  602 - 2 . The first current difference device  602 - 1  receives the current measurement signals Im 1 , Ip 1  from the first and third current meters  506 - 1 ,  506 - 3 , respectively, and the second current difference device  602 - 2  receives the current measurements Im 2  and Ip 2  from the second and fourth current meters  506 - 2 ,  506 - 4 . The outputs of the current difference devices  602 - 1 ,  602 - 2  are amplified, respectively, by amplifiers  604 - 1 ,  604 - 2 . 
         [0045]    A differential amplifier  402  receives, at its inputs, the respective outputs from the amplifiers  604 - 1 ,  604 - 2  and provides a ROTATION signal indicative of a direction and magnitude of rotation. 
         [0046]    A summer  404  adds the outputs of the first and second amplifiers  604 - 1 ,  604 - 2  to arrive at a linear acceleration signal LINEARACCEL indicating the direction and magnitude of linear acceleration, in the example shown in  FIGS. 5A-5D , along the Y axis. 
         [0047]    Referring to  FIGS. 5C and 5D , when the current mode gyroscope  500  is spinning, or linearly accelerating, respectively, the jet streams  224 - 1 ,  224 - 2  will be deflected, as has been described above. 
         [0048]    Advantageously, the current mode sensing gyroscope  500  is a relatively simple device as compared to the prior embodiments described above. It not only removes some structure, for example, the heaters, it also removes the need for the power that would drive the heaters. 
         [0049]    The above-described embodiments of the present invention may be modified in various ways. Referring now to  FIG. 7 , the current mode gyroscope  500  described in  FIGS. 5A-5D  may be configured such that one DC voltage supply  220 - 1 ,  220 - 2  is used, respectively, for the two sides of the device and the current sensing devices  506  then measure the currents found on respective “legs” of the circuits as shown. 
         [0050]    Further, the circuit configuration shown in  FIG. 7  may be modified such that a first current difference device  802 - 1  is used to measure the currents Im 1 , Ip 1  and calculate a difference value therebetween and a second current difference device  802 - 2  provides the difference value between Im 2  and Ip 2 . This would reduce the number of discrete components necessary to support the current mode gyroscope  500 . One of ordinary skill in the art will understand that there are combinations of these alternate devices that may be used. 
         [0051]    It should be appreciated that the circuit diagrams shown in the figures also represent some functional blocks and should not be used to limit the claims to any specific structure unless explicitly recited in a claim. Thus, while an inline current meter is shown above, any one of a number of other known current measuring devices may be used including, but not limited to, Hall effect sensors, magnetoresistive sensors, current clamps and current transformers. 
         [0052]    In another implementation, as shown in  FIG. 9 , two of the ion gyroscopes  200 - 1 ,  200 - 2  may be oriented in opposition to one another. Essentially, as shown in  FIG. 9 , two of these devices may be used to function as the symmetric gyroscope shown in  FIGS. 3A-3D . Of course, one of ordinary skill in the art would understand that the necessary DC power sources and output circuitry would need to be connected although not shown in  FIG. 9  in order to facilitate explanation. Still further, one of ordinary skill in the art would understand that the two devices  200 - 1 ,  200 - 2  would have to be fixedly oriented, i.e., permanently mounted on a structure  902 , with respect to each other such that the linearity of the system is maintained. Accordingly, it may be necessary to calibrate or establish a zero point prior to operation. It is expected, however, that one of ordinary skill in the art would understand how to accomplish this. 
         [0053]    Referring now to  FIG. 10 , a flowchart  950  represents methods in accordance with embodiments of the present invention as described herein. Initially, step  952 , symmetric ion streams are generated. Subsequently, if implementing the heated ion gyroscope, control passes to step  954  where the ion streams are heated. The temperatures are measured on the first and second pairs of thermocouples, step  956 , and those temperatures on the first and second pairs of thermocouples are compared to one another, step  958 . Output signals indicative of rotation and/or linear acceleration as functions of the compared temperatures are then provided, step  960 . 
         [0054]    If the current mode gyroscope is implemented then, step  962 , the currents flowing in the first and second pairs of electrodes are measured. These currents are then compared to one another, step  964 , and subsequently output signals indicative of rotation and linear acceleration are provided as a function of the compared current measurements, step  966 . 
         [0055]    Further, the discrete devices in the measurement circuits  400 ,  600  may be replaced by analog devices, digital devices, hybrid devices, and devices under the control of a microprocessor, e.g., Analog-Digital converters and Digital-Analog converters. These would all be understood by one of ordinary skill in the art. 
         [0056]    Still further, the gyroscope, DC voltage sources, current meters, measurement circuits, etc. may all be combined in a single device having only a power input and output signals to offer a “system on a chip” operability. 
         [0057]    Having thus described several features of at least one embodiment of the present invention, it is to be appreciated that various other alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only, and the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.