JP2017032453A - Method and device for measuring attitude angle using diffraction grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure micro angle displacement amounts about three axes of rolling, pitching, and yawing all together.SOLUTION: The measurement device measures the absolute value of an attitude angle, which the measurement device forms with the direction of gravitational force, by measuring change in the angle of a two-dimensional diffraction grating 2 with the measurement device with an angle measuring mechanism on the basis of the autocollimation method, using the phenomena of the horizontal surface of the two-dimensional diffraction grating 2 floated on the liquid surface of a liquid 4, being held by the gravity.SELECTED DRAWING: Figure 1

Description

  The present invention measures the attitude angle of the measuring device by detecting the angle change of the diffraction grating suspended on the surface of the liquid, using a floating body composed of a two-dimensional diffraction grating, The present invention relates to a method and apparatus for collectively measuring posture angles.

  In the field of precision machining, equipment that accurately measures the three-axis attitude angle of an object is required. Here, the posture angle is defined as rolling, pitching, and yawing as angular displacements around the respective axes of the right-handed system direct coordinates x, y, and z. Conventionally, measurement by an autocollimator has been often used for posture angle measurement.

  The autocollimator is an angle measuring device that irradiates a measurement target with light rays and detects the angle deviation between the incident light and the reflected light. High resolution with sub-angular second order and collective measurement of angles around two axes. Is possible. On the other hand, because the structure is such that light rays are exposed to the atmosphere, if the distance between the autocollimator and the object to be measured increases, the measurement accuracy decreases due to fluctuations in the refractive index of the atmosphere. Since each autocollimator is limited to two axes, there is a problem that at least two autocollimators are required for measuring the three-axis attitude angle.

  On the other hand, the merit of the angle measuring method using the gyro rate sensor is that a relative attitude angle change is measured based on the integration of the angular velocity, and therefore no external reference is required. In addition, three axes of rolling, pitching and yawing can be measured by preparing gyro rate sensors for three axes. In the precision measurement field, it is used as a parallelism measurement device for rolls in roll-to-roll processing equipment (Non-patent Document 1). This roll parallelism measuring device incorporates three-axis ring laser gyros (Non-Patent Documents 2 and 3) at right angles to each other, and the three-axis measurement accuracy of rolling, pitching and yawing is calculated by converting the parallelism into an angle. It is ± 0.0028 ° (resolution 0.00022 °), and has sufficient accuracy and resolution that can be used even in precision engineering. However, since the gyro rate sensor calculates the angle by time-integrating the angular velocity, the stability of the sensor greatly affects the measurement result (Non-Patent Document 4). This stability is called the bias stability of the gyro rate sensor (Non-Patent Document 5), and considering the long-time angle measurement by the gyro rate sensor, the occurrence of an error proportional to time is expected due to the presence of the bias stability. Is done. The ring laser gyro used in the above-described roll parallelism measuring apparatus has a low bias stability value among 0.01 ° / hour (see Non-Patent Documents 4 and 5) and commercially available gyro rate sensors. However, an error of up to 0.01 ° per hour is still expected. Therefore, it can be seen that it is difficult to maintain accuracy in measurement over a long time.

  Further, the use of the ring laser gyro described above is limited from the viewpoint of being very expensive. In addition, as a ring laser gyro with extremely low bias stability, research on seismo vibration measurement used in gravitational wave detection devices in astronomy has been conducted (Non-Patent Documents 6 and 7), but the optical path length is on the order of meters. Since it is large, it is not a realistic size and weight for industrial use. Therefore, it is considered that precise measurement with a gyro rate sensor is difficult.

  In addition, posture angle measurement using a tilt sensor is applicable only to rolling and pitching measurements because it does not cause an integration error compared to posture angle measurement using a gyro rate sensor. is there. The attitude angle is the angle with respect to the gravity axis, and the displacement in the direction of gravity on the earth is stable at 0.1 "or less (Non-Patent Document 8), so high accuracy can be expected. It is classified into several types according to the detection method, and typical ones are the pendulum type (Non-Patent Document 9-13), the accelerometer type, and the liquid level reference type (Non-Patent Documents 14 to 18). The pendulum type has a pendulum supported by a rotating shaft or held by an elastic body inside the sensor.When a posture angle is applied to the sensor, the pendulum causes an angular displacement from the initial position so as to be parallel to the gravitational acceleration. The attitude angle is measured from the relative angle between the sensor housing and pendulum by reading it with an angle sensor.In the accelerometer method, gravitational acceleration is detected using a single-axis or multi-axis accelerometer, and the acceleration of each axis is measured. Calculate the direction of gravitational acceleration from the detected value of Is obtained as. Liquid-referencing can be classified into two methods of detecting the movement of the bubble method and in the liquid to detect the liquid level.

  The method of detecting the liquid level utilizes the fact that the liquid level of the liquid sealed inside the sensor becomes horizontal due to gravity, and converts the change in the liquid level into a posture angle. As a tilt sensor based on a horizontal surface created by a liquid that can measure two-axis attitude angles of rolling and pitching, it has an accuracy of ± 0.4 "using a commercial product with an angular resolution of 3.6" and refraction on the liquid surface. Sensors have also been studied (see Non-Patent Document 19). However, in any tilt sensor, the number of measurement axes is limited to two. This is because the gravitational acceleration vector is a direction vector and has only three components of rolling, pitching, and gravitational acceleration. The orientation component that is the rotational component around the gravitational acceleration vector, that is, the yawing attitude angle, Measurement was impossible in principle. This is a phenomenon common to all tilt sensors including a pendulum type and an accelerometer type as well as a liquid level based tilt sensor.

  On the other hand, in order to perform a three-axis attitude angle measurement using an inclination sensor, a new method for detecting a yawing attitude change is required. A simple method is to combine a tilt sensor and another attitude angle sensor capable of measuring yawing. Examples of sensors capable of measuring yawing include a magnetic compass, a mechanical compass, and a gyro rate sensor. The magnetic compass is a sensor that indicates magnetic north at an arbitrary point on the earth (excluding the polar region), and can measure the absolute value of the attitude angle of yawing. However, the accuracy of commercially available products is limited to ± 0.1 ", and because the magnetic field lines of weak geomagnetism are detected, there is a possibility of being affected by external magnetism, which is not suitable for high-accuracy posture angle measurement. A mechanical compass is a sensor that indicates the true north at any point on the earth using the gyro effect (the direction of the axis of rotation is north), and measures the absolute value of the yaw attitude angle in the same way as the magnetic compass. Is possible.

  However, this is also unsuitable for use in a highly accurate attitude angle measurement application with a precision of ± 0.3 ° on the market. As described above, the gyro rate sensor can achieve high resolution in a short time, but drift of the angle measurement value due to time integration occurs. Therefore, when performing long-time measurement, the ring laser gyro with the highest performance for consumer use is used. Even when using, a drift of 36 "/ hour is predicted. In order to measure 3-component rolling, pitching and yawing of an object in space, a yawing detection mechanism separate from the tilt sensor is required. Conventionally, the attitude heading reference system (AHRS) has been used in aerospace applications, which is a ring laser that is a highly stable gyro-rate sensor for measuring the three-axis attitude angles described above. A sensor system that combines a gyro, a tilt sensor for periodically resetting the integration error of the gyro rate sensor, and a magnetic compass for azimuth detection. That.

Tomoaki Yokono and Tomoaki Yokono, “Roll parallel alignment measurement using a ring laser gyro--Preventive diagnosis technology to prevent the occurrence of defective webs,” Convertech, vol. 39, no. 4, pp. 100-103 (2011 ). E. Sanders, “The laser,” Rev. Mod. Phys., Vol. 57, no. 1, p. 61. (1985). ERIC UDD, “Fiber Optic Sensors Section9_FIBER OPTIC SENSORS BASED ON THE SAGNAC INTERFEROMETER AND PASSIVE RING RESONATOR,” Second., E. U. W. B. S. Jr., Ed. John Wiley & Sons, Inc., pp. 199-230, (2011). N. M. Barbour, “Inertial Navigation Sensors,” vol. 116, pp. 1-28, 2011. Edited by Tamagawa Seiki, `` Gyro Sensor Technology: Point Explanation '', Tokyo Denki University Press, (2011). K. U. Schreiber and J. P. R. Wells, “Invited Review Article: Large ring lasers for rotation sensing,” Rev. Sci. Instrum., Vol. 84, no. 2013, (2013). KU Schreiber, JN Hautmann, a. Velikoseltsev, J. Wassermann, H. Igel, J. Otero, F. Vernon, and JPR Wells, “Ring laser measurements of ground rotations for seismology,” Bull. Seismol. Soc. Am., vol. 99, no. 2, pp. 1190-1198, (2009). M. P. Thekaekara and R. Appler, “Mercury Pool for Precise Alignment of Instruments,” Rev. Sci. Instrum., Vol. 36, no. 5, p. 644, (1965). K.-C. Fan, T.-H. Wang, S.-Y. Lin, and Y.-C. Liu,: Design of a dual-axis optoelectronic level for precision angle measurements, Meas. Sci. Technol., 22, 5, 055302, (2011). K. Venkateswara, C. a Hagedorn, M. D. Turner, T. Arp, and J. H. Gundlach: A high-precision mechanical absolute-rotation sensor., Rev. Sci. Instrum., 85, 1, 015005, (2014). H. Bao, X. Dong, C. Zhao, L.-YL Shao, CC Chan, and P. Shum, “Temperature-insensitive FBG tilt sensor with a large measurement range,” Opt. Commun., Vol. 283, no . 6, pp. 968-970, (2010). J. Liang, T. Matsuo, F. Kohsaka, X. Li, K. Kunitomo, and T. Ueda, “Fabrication of two-axis quartz MEMS-based capacitive tilt sensor,” IEEJ Trans. Sensors Micromachines, vol. 128, no. 3, pp. 85-90, (2008). Y. Cheng, J. Winterflood, L. Ju, and D. G. Blair, “Tilt sensor and servo control system for gravitational wave detection,” Class. Quantum Gravity, vol. 19, no. 7, p. 1723, (2002). Z. W. Zhong, L. P. Zhao, and H. H. Lin, “Development and investigation of an optical tilt sensor,” Opt. Commun., Vol. 261, no. 1, pp. 23-28, (2006). H. Jung, C. C. J. Kim, and S. H. S. Kong, “An optimized MEMS-based electrolytic tilt sensor,” Sensors Actuators A Phys., Vol. 139, no. 1, pp. 23-30, (2007). D. Welch, J. Georgiou, and J. B. Christen, “Fully differential current-mode MEMS dual-axis optical inclination sensor,” Sensors Actuators A Phys., (2012). Y. Z. Xing and F. Schneider, “A bubble-level tilt sensor with a large measurement range,” Sensors and Actuators, vol. 17, no. 3, pp. 339-344, (1989). H. Jung, C. C. J. Kim, and S. H. S. Kong ,: An optimized MEMS-based electrolytic tilt sensor, Sensors Actuators A Phys., Vol. 139, no.1, pp. 23-30, (2007). J. Torng, C.-H. Wang, Z.-N. Huang, and K.-C. Fan, “A novel dual-axis optoelectronic level with refraction principle,” Meas. Sci. Technol., Vol. 24, no. 3, p. 035902, (2013).

  In the sensor that performs the spatial posture measurement as described above, detection of a large posture change on the order of several tens of degrees is assumed, and a high resolution of the sub-angular second order cannot be obtained. Furthermore, since it is attitude angle measurement using a ring laser gyro, the cost per number of axes is very high, and there is a problem in usability. As described above, in the measurement of the yawing attitude angle change, there is a problem that it is difficult to achieve both resolution and cost.

  Therefore, in the present invention, a triaxial attitude angle with the gravitational direction as a reference direction, which can measure a minute angular displacement simultaneously with the three axes of rolling, pitching and yawing, which is impossible with a conventional biaxial attitude angle sensor. It aims to provide a sensor.

  In view of this, the present inventors have conceived a method in which a diffraction grating is levitated on the liquid surface and its attitude angle is measured by a three-axis angle sensor (for example, Japanese Patent No. 5322099) using a laser diffraction phenomenon. Accordingly, the relative angle of the posture between the sensor and the diffraction grating can be measured by utilizing the fact that the normal line of the laser irradiation surface of the diffraction grating matches the normal line of the liquid surface. That is, by measuring the attitude angles of the two axes of rolling and pitching and further increasing the moment of inertia of yawing of the diffraction grating, the diffraction grating always points in a certain direction in space even if the entire sensor yaws. Become.

  Therefore, by measuring the yaw attitude angular displacement of the diffraction grating and the entire sensor by the three-axis angle sensor, it becomes possible to detect an angular change around the yawing from the initial state of the entire sensor. Accordingly, it is possible to provide a posture angle sensor that can be used at any point on the earth and that can measure a three-axis angular displacement.

  According to the present invention, when a liquid is enclosed in a container built in the sensor, the diffraction grating is floated on the liquid surface, and laser light is irradiated toward the diffraction grating from the triaxial angle sensor built in the sensor. N-order diffracted light (N = 0, ± 1, ± 2 ...) generated in the light is received by the light receiving element inside the angle sensor, and the light on the light receiving element when the attitude angle of the diffraction grating is displaced around rolling, pitching, and yawing By detecting and calculating the position change amount of the spot, the three-axis angular displacement can be measured with reference to the diffraction grating suspended on the liquid surface. For this reason, it is possible to perform angle measurement without installing an angle reference standard such as a mirror or a diffraction grating outside the sensor, so that both resolution and cost can be achieved in spatial attitude measurement including yawing attitude angle change measurement. The effect that it can be obtained.

Basic configuration of triaxial attitude angle sensor according to an embodiment of the present invention A diffraction grating fixed to a floating body in a three-axis attitude angle sensor according to an embodiment of the present invention Principle of detection of change in posture angle around pitching in a triaxial posture angle sensor according to an embodiment of the present invention Principle of detection of posture angle change around yawing in a triaxial posture angle sensor according to an embodiment of the present invention

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an apparatus front view showing a basic configuration of a triaxial attitude angle sensor according to an embodiment of the present invention. The diffraction grating (two-dimensional diffraction grating) 2 is fixed to the floating body 1 and is held in a floating state on the liquid surface by the liquid 4 filled in the container 3. The laser beam 13 irradiated from the laser light source 5 and collimated by the collimating lens 6 is irradiated to the diffraction grating 2 through the beam splitter 7 and the polarizing plate 8, and the 0th order, ± 1st order, ± 2nd order ... ± Nth order diffraction. Produce light.
In the present embodiment, as shown in FIG. 2, the 0th-order diffracted light 14 is collected by the lens 9 shown in FIG. 1 and detected by the light receiving element 10, and the + 1st-order diffracted light 15a is collected by the lens 11 shown in FIG. Light is detected by the light receiving element 12. Thereby, the light spot position change on each light receiving element is detected. In the present embodiment, the first-order diffracted light 15b is not used.
As described above, in this embodiment, it is possible to measure the relative angle between the angle sensor and the diffraction grating by measuring using the angle measuring mechanism built in the angle sensor based on the laser autocollimation method. It is. In other words, by detecting the diffracted light when the diffraction grating is irradiated with laser light with the light receiving element and detecting the change in the light spot position on the light receiving element, the change in the attitude angle, which is the angle that the angle sensor forms with the direction of gravity. Can be measured. Here, by simultaneously measuring the change in the light spot position of the first-order diffracted light, the change in the angle around the three axes can be detected simultaneously and the change in the posture angle can be accurately measured and evaluated.
As shown in FIG. 3, the diffraction grating 2 is fixed to the floating body 1, and the diffraction grating installation surface of the floating body 1 is parallel to the liquid surface, so that the optical action surface of the diffraction grating 2 is a horizontal plane. Therefore, the angle sensor measures the angle between itself and the horizontal plane, and the posture angle can be measured. Therefore, according to this principle, it is possible to measure the posture angle around rolling and pitching, and the measurement result is acquired as the posture angle change around the rolling and pitching of the sensor.

  Next, the measurement principle of the angular displacement around the yawing will be described with respect to the three-axis attitude angle sensor configured as described above. FIG. 4 shows a state of the floating body 1 and a diffraction grating (not shown) fixed thereto when the entire sensor rotates around the yawing. In the present embodiment, it is utilized that the change in the light spot position on the light receiving element caused by the change in the attitude angle around the yawing is generated in the first-order diffracted light. Here, the equation of motion of rotation around the yawing of the floating body is expressed by Equation 1.

  Here, q: angle around the yawing of the floating body, I: moment of inertia around the yawing of the floating body, t: external force torque applied around the yawing of the floating body, and t: time. When this differential equation is integrated once in time, Equation 2 is obtained.

  Here, r indicates the distance from the center of the container 3, and C1 is an integral constant. Furthermore, the time response of the angle around the yawing of the floating body is obtained as shown in Equation 3 by integrating Equation 2 twice over time.

  Here, C2 is an integral constant. If the floating body 2 is stationary around the yawing in the initial state, C1 = 0 and C2 = 0. Therefore, Formula 3 shows that it is dominated by the inertia moment I around the yawing of the floating body and the external force torque τ applied around the yawing of the floating body. Therefore, when I is sufficiently large and τ is sufficiently small, the angle change around the yawing generated in the floating body 2 becomes very small.

  In other words, the floating body 2 does not rotate around the yawing and always points in a certain direction. When an arbitrary posture angle change around the yawing is given to the three-axis posture angle sensor of the present invention, the floating body 2 holds the initial angle, but the sensor casing rotates by the given angle change, An angle change around the yawing occurs between the three-axis angle sensor and the diffraction grating.

  Therefore, by measuring this angle change with a three-axis angle sensor, it is possible to measure the attitude angle change from the initial state around the yawing. The above is the detection principle of the posture angle change around the yawing of the present invention.

  By using the present invention, it is possible to measure the change in the attitude angle based on the gravitational acceleration vector, so there is no need to use a large and expensive external reference, and the measuring device can be installed freely, so that the positioning device and the drive mechanism can be installed. Applications can be expected, and its industrial applicability is high.

DESCRIPTION OF SYMBOLS 1 Floating body 2 Diffraction grating 3 Container 4 Liquid 5 Laser light source 6 Collimating lens 7 Beam splitter 8 Polarizing plate 9 Lens 10 Light receiving element 11 Lens 12 Light receiving element 13 Laser beam 14 0th order diffracted light 15a + 1st order diffracted light 15b-1st order diffracted light

Claims (5)

A posture angle measurement method for detecting a change in the posture angle of a measuring device using a grating plane when a two-dimensional diffraction grating is suspended on a liquid surface under gravity as a reference horizontal plane,
An attitude angle that is an angle formed by the measuring device with respect to the direction of gravity by detecting a diffracted light when the two-dimensional diffraction grating is irradiated with a laser beam with a light receiving element and detecting a change in a light spot position on the light receiving element. A posture angle measuring method, characterized by measuring a change in the angle. In the posture angle measuring method according to claim 1,
By simultaneously detecting the diffracted light of the laser light irradiated on the two-dimensional diffraction grating by a plurality of light receiving elements mounted in the measuring apparatus, changes in attitude angles around three axes are collectively measured. A posture angle measuring method characterized by: In the attitude angle measuring method according to claim 1 or 2,
Using the fact that the reflecting surface of the two-dimensional diffraction grating suspended on the liquid surface is kept horizontal by gravity, the absolute angle of the posture angle can be obtained without using a reference standard provided outside the measuring apparatus. A posture angle measuring method characterized by measuring an angle. In the attitude angle measuring method according to any one of claims 1 to 3,
A posture angle measuring method, wherein a change in a light spot position on the light receiving element caused by a change in posture angle around a yawing is generated in the first-order diffracted light of the diffracted light. A two-dimensional diffraction grating,
A container in which a liquid for floating the two-dimensional diffraction grating is stored;
A light source for irradiating the two-dimensional diffraction grating suspended on the liquid surface under gravity with a laser beam;
A light receiving element for detecting diffracted light when the two-dimensional diffraction grating is irradiated with the laser light;
A posture angle measuring device comprising: a measuring unit that measures a change in posture angle by detecting a light spot position change on the light receiving element.