Rotation table with tiltable sensor holder

Abstract

The invention relates to a device for conducting tests for characterizing an inertial sensor (1), comprising: a stationary base element (3) and a rotation table (5) rotatably mounted thereon, which has a holder (7) for the inertial sensor (1) and for a reference sensor unit (9); a motor (11) for rotating the rotation table (5); a reference rotary encoder (13) for determining a current rotational position of the rotation table (5); a vibration generator unit (15) for generating reference accelerations on the rotation table (5); and a vibration detection unit (17) for detecting reference accelerations actually present on the rotation table (5). The holder (7) can be tilted relative to the rotation table (5).

Description

The invention relates to a device for carrying out tests for the characterization and / or calibration of an inertial sensor, and to a method for carrying out tests for the characterization and / or calibration of an inertial sensor.Inertial measurement units (so-called IMUs) serve to record current kinematic variables in a reference coordinate system. Embodied largely mechanically, they use known effects, such as the relationship between force and accelerated mass, the positional angle stability of rotating masses (gyro stability) and the like, in order to ascertain sensor signals of prevailing kinematic variables that can be processed further.The following information arises from specialist considerations, rather than necessarily from a specific prior art document: as for other sensors it is also the purpose of inertial measurement units to detect a naturally occurring quantity and to generate a processable signal value therefrom. Naturally, each physical sensor has certain inaccuracies that can be influenced by environmental conditions and in particular vary over different ranges of measured variables and / or frequencies of the measured variable. A sensor thus has a certain transfer function (in the algebraic as well as in the dynamic sense), which represents a mapping of the naturally occurring variable onto the processable sensor signal.Such a transfer function can be described using mathematical models. A large number of model types are possible in principle for this purpose, whether they be models in the form of algebraic equations or dynamic models, the latter describing a frequency-dependent transfer function and thus preferably being formulated as differential equations or as equations in the frequency range (such as the Laplace range). Linear models can also be distinguished from nonlinear models. Statistical models allow many individual empirical data to be combined into one model. The more accurately a model images the reality of the sensor, the better the error introduced by the respective sensor in the transmission can be corrected from the naturally occurring variable to the processable sensor signal.A frequently essential component of an inertial measurement unit is gyro instruments. Gyro instruments of this type serve to be able to determine the orientation of a reference coordinate system in the form of position angles, in particular with respect to the earth. The effect utilized in this case is the stability of a rotating mass with respect to changes in position angle. If, for example, a gimbaled rapidly rotating mass is arranged in a housing on a moving body, during a rotational movement of the body and thus of the housing, the housing is rotated around the rotating mass, so to speak, while the respective axis of the rotating mass maintains its orientation. From this relative change in orientation between rotating mass and housing, an change in orientation in the form of differential angles can thus be determined. If a position angle is determined by temporal integration of a measured rotation rate, measurement errors in the measured rotation rate naturally integrate into larger errors in the position angles. To avoid this error integration, gyro instruments are typically not used alone, but rather are coupled to other types of sensors. Nevertheless, the measurement error in the measured rotation rate enters into the position angle finally determined.With the aim of reducing sensor errors of gyro instruments such as rotation rate sensors, gyro instruments of this type have been and are typically tested for characterization in the sense of a system identification in order to eliminate errors in later operation, i.e. in order to calibrate the gyro instruments, by means of the characterization and the knowledge about transmission errors of the gyro instruments achieved therewith.In order to characterize an inertial sensor, for example a rotation rate sensor, under certain circumstances with the aim of calibration, a rotary table can be used, with the aid of which the inertial sensor can be subjected to a rotational movement.CN 1 15 876 224 A relates in the following context to an integrated simulation and measurement system for a triaxial electric rotary table with a base and a control box, which are designed in an integrated manner. The triaxial turntable is located on a base and the control box is located on the bottom of the base; the triaxial turntable comprises a component of movement of the inner frame, a component of movement of the middle frame and a component of movement of the outer frame, wherein the component of movement of the outer frame comprises a base plate of the outer frame and two oppositely arranged vertical plates of the outer frame, and the base plate of the outer frame and the two oppositely arranged vertical plates of the outer frame together form a U-shaped structure.US 2011 / 0202 300 A1 further relates to a rotary table, the upper side of which is horizontal. A pose detection unit is attached to one side of a cubic holder such that an X axis perpendicularly intersects a first side, a Y axis perpendicularly intersects another side, and a Z axis perpendicularly intersects the first side, in turn.It is an object of the invention to provide a rotary table with the aid of which efficient tests for data acquisition for the characterization and / or calibration of an inertial sensor can be carried out.The invention results from the features of the independent claims. Advantageous refinements and refinements are the subject matter of the dependent claims.A first aspect of the invention relates to a device for carrying out tests for the characterization and / or calibration of an inertial sensor, comprising:a stationary base element and a rotary table rotatably mounted on the base element, wherein the rotary table has a receptacle for the inertial sensor and for a reference sensor unit;a motor connected to the rotating table for rotating the rotating table relative to the base member about a rotation axis;a reference rotation meter for determining a current rotational position and a current rotational rate of the rotating table with respect to the base member;a vibration generating unit for generating reference accelerations on the rotary table;a vibration detection unit for detecting reference accelerations and reference displacements of the rotary table which are actually present on the rotary table;a control unit which is configured and designed for the purpose of carrying out the following:Vibration generator unit for generating reference accelerations and at the same time for controlling the motor for rotating the rotary table with respect to the base element; wherein the receptacle is tiltable with respect to the rotary table, such that an orientation of the inertial sensor can be changed together with an orientation of the reference sensor unit with respect to the axis of rotation of the rotary table without the inertial sensor being required to be removed from the receptacle for its change of orientation.The control unit is configured to drive the vibration generator to generate reference accelerations and simultaneously drive the motor to rotate the rotary table with respect to the base member. Thus, both rotations and vibrations are simultaneously applied to the inertial sensor to be examined. The rotary table thus forms a centrifuge which is designed for corresponding loads of vibrations on it. The reference rotation meter and the vibration detection unit allow recording of a time series of rotations in time association with the vibrations.A slip ring may be provided between the rotary table and the base member to energize the inertial sensor while being rotationally moved by rotation of the rotary table relative to the base member. Alternatively or additionally, the slip ring can be used to conduct a data stream comprising sensor signals of the inertial sensor and ideally also of the reference sensor unit from the rotating rotary table.In the connection between the rotary table and the base element, care should be taken that both are connected to one another as rigidly as possible, with the exception of the degree of freedom for rotating the rotary table. Particularly preferably, roller bearings as rigid as possible, such as ball bearings, are provided between the rotary table and the base element in order to avoid a translatory displacement of the two with respect to one another, in particular if the vibration generator unit is arranged in such a way that it vibrates the base element together with the rotary table. In this case, a connection to the vibration generator unit that is as stiff as possible is also advantageously to be provided. The device should also be designed so that the natural frequencies are as high as possible, that is to say ideally well above the excitation frequencies, in order to reduce the influence of the device on the sensor to be tested.Preferably, the vibration detection unit includes one or more acceleration sensors for actually detecting the vibration of the vibration table. The vibration detection unit may also be disposed in the base member when the rotary table is configured to collectively perform the vibrations generated by the vibration generating unit together with the base member. The vibrations can also be determined by deflection sensors of the vibration detection unit, so that instead of the accelerations of the rotary table (or of the base element) positions are determined which, however, are kinematically equivalent by the accelerations which can also be measured. Also equivalent is a measurement of speeds caused by the vibrations.Preferably, primary sensor axes of the vibration detection unit have non-zero inclination angles with respect to the axis of rotation of the rotary table. In particular, if one or more acceleration sensors are used, these are installed at a corresponding angle with respect to the axis of rotation, particularly preferably in or on the base element. Furthermore, the primary sensor axes are preferably situated on the surface of a cone having the axis of rotation as the axis of rotational symmetry of the cone, i.e., preferably distributed around a circumference around the axis of rotation.The reference rotation meter is to measure an absolute position and a rotation rate between the rotation table and the base member. For direct measurement, various optical and / or magnetic sensor elements can be arranged in particular along an outer region with respect to the diameter of the rotary table in order to detect pulses which are directly characteristic for specific orientations of the rotary table. Absolute encoders are also an option as long as the influence of the vibrations in their signals can be reduced as much as possible. Positions of the rotary table can also be derived from the measurement of rotation rates.Since the receptacle for the inertial sensor is tiltable with respect to the rotary table, it is possible to test the inertial sensor in at least two different main load directions by rotating the inertial sensor, in particular with its housing, in its orientation accordingly with respect to the rotary table. Advantageously, no changes in uncertainties in the orientation with respect to the rotary table occur between the tests with their respective orientation of the inertial sensor; the so-called misalignment remains constant together with the inertial sensor during the change in orientation of the recording. This orientation error, called misalignment, therefore also does not change with respect to the reference sensor unit, which is likewise arranged on the receptacle in a fixed manner to the body. A change in the orientation of the inertial sensor is thus always also identical to a change in the orientation of the reference sensor unit by tilting the receptacle.This circumstance advantageously leads to being able to characterize the inertial sensor and orientation errors (misalignments) of the recording. Because the accelerations arising at the inertial sensor from vibrations and the exactly known rotation of the rotary table and the accelerations acting on the inertial sensor due to the rotation are exactly known for all tests, and because direct measurements of rotation rates and / or accelerations are available at the receptacle with the reference sensor unit, a reference is known, i.e. a ground truth of data about influences which actually act on the tested inertial sensor. These known reference variables, together with the temporarily assigned sensor signal of the inertial sensor in the test, allow an accurate characterization of the inertial sensor, for example, by a least squares method.The reference sensor unit, arranged on the receptacle in / to which the inertial sensor to be tested can be arranged, supplies the information which is necessary to estimate the orientation of the receptacle relative to the reference accelerations and the axis of rotation of the rotary table, even if the reference sensor unit is under the influence of the vibrations for the reference accelerations and the rotation of the rotary table, which tends to degrade the information. What is decisive for the data of the reference sensor unit is that it is provided in a body-fixed manner for recording together with the inertial sensor, so that the reference of the reference sensor unit remains unchanged relative to the inertial sensor in the event of a change in the orientation of the recording.The apparatus allows not only to generate sufficient excitation to observe the behavior of an inertial sensor with simultaneous vibration and rotation, but also to characterize such a sensor with high accuracy. This is achieved in particular in that rotation and vibration can be applied to the tested inertial sensor simultaneously in order to enable complete observation of the behavior of the inertial sensor.According to an advantageous embodiment, the vibration detection unit has at least one acceleration sensor.According to a further advantageous embodiment, the vibration detection unit has a plurality of acceleration sensors, the measurement directions of which each have an angle to the axis of rotation.According to a further advantageous embodiment, the vibration detection unit has a multiplicity of acceleration sensors, wherein measurement directions of the acceleration sensors each have an angle to a provided direction of the reference accelerations.According to a further advantageous embodiment, the vibration detection unit is arranged in or on the base element.According to a further advantageous embodiment, for a rotation sensor, in particular a rotation rate sensor, the sensor signals of the inertial sensor are read out as an inertial sensor for at least two different alignments of the recording relative to the rotation table, in each case under vibrations which are generated by the vibration generator unit and under the rotation of the rotation table, and are compared with reference signals from at least the reference sensor unit.According to a further advantageous embodiment, for an acceleration sensor as an inertial sensor, the sensor signals of the inertial sensor are read out for at least two different alignments of the receptacle relative to the provided direction of the reference accelerations, which are compared with reference signals at least from the reference sensor unit by different possible combinations of the alignment between the receptacle with respect to the rotary table, the angular position of the rotary table with respect to the base element and the alignment of the vibration generator unit, in each case under vibrations which are generated by the vibration generator unit and optionally under rotation of the rotary table.According to a further advantageous embodiment, the device further comprises a temperature regulating device for setting a desired temperature at the inertial sensor when the sensor is accommodated in the receptacle.For this purpose, a Peltier element can be provided, the receptacle and / or the rotary table being used as a heat sink. Furthermore, a temperature sensor is advantageously provided for this purpose in order to set a desired temperature, and in order to use the temperature data, associated with the vibrations and rotations, for characterizing the inertial sensor.According to a further advantageous embodiment, the vibration generator unit is designed to generate reference accelerations in at least two axes, particularly preferably along and transversely to the axis of rotation.A further aspect of the invention relates to a method for carrying out tests for the characterization and / or calibration of an inertial sensor, wherein a device is used which has a stationary base element and a rotary table rotatably mounted on the base element, wherein the rotary table has a receptacle for the inertial sensor and for a reference sensor unit, and the device has a motor connected to the rotary table for rotating the rotary table with respect to the base element about an axis of rotation, a reference rotation meter for determining a current rotational position and rotational rate of the rotary table with respect to the base element, a vibration generator unit for generating reference accelerations on the rotary table, a vibration detection unit for detecting reference accelerations actually present on the rotary table or translatory positions of the rotary table resulting therefrom, and a control unit, the vibration generating unit controls the vibration generating unit to generate reference accelerations and simultaneously the motor to rotate the rotary table with respect to the base element, and wherein the receptacle on the rotary table is tiltable; wherein an orientation of the inertial sensor is changed together with an orientation of the reference sensor unit with respect to the axis of rotation of the rotary table without removing the inertial sensor from the receptacle by tilting the receptacle, and wherein sensor signals of the inertial sensor arranged on the receptacle are read out and compared with reference signals from at least the reference sensor unit.The reference signals are preferably determined from the signals of the reference sensor unit, the vibration detection unit, and the signals of the reference tachometer. Thus, different data sources for the reference signals are available, partly from a non-rotating system and partly from the rotating system of the recording.According to a further advantageous specific embodiment, a rotation rate sensor or an acceleration sensor is used as the inertial sensor.According to a further advantageous embodiment, a sensor fusion of the signals of the reference sensor unit, the vibration detection unit and the reference revolution sensor is carried out, and the result of the sensor fusion is used to determine reference signals, wherein the reference signals are compared with the sensor signals of the inertial sensor.Accurate absolute data about position during vibration and rotation is available. This data, when fused to the data of the reference sensor unit, increases the accuracy of the estimated accelerations and rotations on the recording by the intrinsic higher accuracy and by the fact that they do not introduce drift. A sensor fusion algorithm, which fuses the various reference signals in order to obtain accurate information about rotation and acceleration at the recording, provides an even more accurate reference for characterizing the initial sensor.According to a further advantageous embodiment, an orientation error and a bias of the signals of the reference sensor unit and / or of the vibration detection unit and / or of the reference revolution meter, preferably of all three, or of the reference signals, are estimated and preferably also compensated when the reference signals are obtained with the sensor fusion in order to generate more accurate reference signals.The orientation error is also called misalignment. This misalignment and a sensor bias, i.e. a deviation of the sensor signal from the physically present value, is made possible in particular by the inclined orientation of acceleration sensors of the vibration detection unit. Due to the different experimental conditions by means of the rotation of the receptacle for the inertial sensor relative to the axis of rotation and the sufficient dynamic excitation by rotation profiles and vibration profiles, which are controlled by the control unit, are sufficient to derive the misalignments and biases of the sensors, which are used for deriving the reference signals. This provides the basis for calculating the actual orientation of the acquisition, for in turn deriving therefrom the final estimates of the reference signals, and for deriving a more accurate estimate of a bias possibly arising from the vibrations on the rotary table.Advantages and preferred refinements of the proposed method result from an analogous and analogous transfer of the explanations given above in connection with the proposed device.Further advantages, features and details are evident from the following description, in which--possibly with reference to the drawing--at least one exemplary embodiment is described in detail.The following are shown: FIG. 1 : A base element and a rotating table of a device for carrying out tests for characterizing an inertial sensor according to an exemplary embodiment of the invention. FIG. 2 : shows a rotary table with a receptacle in a first orientation according to an exemplary embodiment of the invention. FIG. 3 : The rotary table of FIG. 2 with the receptacle in a second orientation. FIG. 4 : shows a rotary table with a vibration generator unit for vertical vibrations with the receptacle in a first orientation according to an exemplary embodiment of the invention. FIG. 5 : shows a rotary table with a vibration generator unit for horizontal vibrations with the receptacle in a first orientation according to an exemplary embodiment of the invention. FIG. 6 : shows a rotary table with a vibration generator unit for vertical vibrations with the receptacle in a second orientation according to an exemplary embodiment of the invention. FIG. 7 : shows a rotary table with a vibration generator unit for horizontal vibrations with the receptacle in a second orientation according to an exemplary embodiment of the invention.The representations in the figures are schematic and not to scale.FIG. 1 shows a lower part of a device for carrying out tests for characterizing and / or calibrating an inertial sensor 1, in particular a rotation rate sensor. A stationary base element 3 serves to position the apparatus on a planar working surface. A rotary table 5 is mounted on the base element 3, which is secured against translatory displacements with respect to the base element 3 by means of roller bearings which roll on the outer edge of the upper lateral side of the rotary table 5. Two electric motors 11 rotate the rotary table 5 relative to the base element 3 about an axis of rotation as outlined in FIG. 1. A left and right reference rotation meter 13 is also used to determine a current rotational position of the rotary table 5 with respect to the base element 3. Two acceleration sensors of a vibration detection unit 17 arranged on the base element 3 are used to detect reference accelerations which are actually present on the base element 3 and are generated by a vibration generator unit 15 (see FIG. 4 et seq.). By means of a control unit, this vibration generator unit 15 is controlled to generate reference accelerations, and at the same time, the motor 11 is controlled to rotate the rotary table 5 with respect to the base element 3.FIG. 2 shows details of the rotary table 5, which has a receptacle 7 for the inertial sensor 1 and for a reference sensor unit 9 with two acceleration sensors. The receptacle 7 is designed such that the inertial sensor 1 can be received therein and removed again. In addition, the receptacle 7 is tiltable with respect to the rotary table 5, so that an orientation of the inertial sensor 1 can be changed together with an orientation of the reference sensor unit 9 with respect to the axis of rotation of the rotary table 5, without the inertial sensor 1 being required to be removed from the receptacle 7 for its change of orientation.FIG. 3 shows the receptacle 7 in a tilted state with respect to the state from FIG. 2 The change in orientation of the receptacle 7 with respect to the rotation table 5 can be effected in such a way that, in both orientations of the receptacle 7, as shown in FIGS. 2 and 3, the initial sensor 1 can be tested sequentially without having to be removed from the receptacle 7 for the change in orientation.FIG. 4 shows the rotary table 5 with the receptacle 7 in the folded-down position, wherein the component of the vibration generator unit 15 is also shown, which is responsible for vibrations on the rotary table 5 which are directed along the axis of rotation of the rotary table 5 with respect to the base element 3. These are translatory vibrations. A position sensor of a vibration detection unit 17 measuring in the direction of the axis of rotation measures the exact deflection of the rotary table 5 due to the vibrations over time.FIG. 5 shows the rotary table 5 with the receptacle 7 in an opened position, wherein the component of the vibration generator unit 15 is also shown, which is responsible for vibrations on the rotary table 5 which are directed transversely with respect to the axis of rotation of the rotary table 5 with respect to the base element 3. These are likewise translatory vibrations. A position sensor of the vibration detection unit 17 measuring transversely to the axis of rotation measures the exact deflection of the rotary table 5 over time.FIGS. 6 and 7 correspond to the representations of FIGS. 4 and 5, but here the receptacle 7 is shown in each case in a changed orientation with respect to the rotary table 5.Although the invention has been illustrated and explained in more detail by preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a large number of possible variations exist. It is also clear that embodiments mentioned by way of example represent only examples which are not to be understood in any way as limiting, for example, the scope of protection, the possible applications or the configuration of the invention. Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, wherein the person skilled in the art, knowing the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without departing from the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description.List of reference characters1 Inertial sensor in test 3 Base member 5 Rotary table 7 Holder 9 Reference sensor unit 11 Motor 13 Reference rotary meter 15 Vibration generating unit 17 Vibration detecting unit

Claims

Device for carrying out tests for the characterization and / or calibration of an inertial sensor (1), comprising: - a stationary base element (3) and a rotary table (5) rotatably mounted on the base element (3), wherein the rotary table (5) comprises a receptacle (7) for the inertial sensor (1) and for a reference sensor unit (9); - a motor (11) connected to the rotary table (5) for rotating the rotary table (5) with respect to the base element (3) about an axis of rotation; - a reference rotary cutter (13) for determining a current rotational position and rotational rate of the rotary table (5) with respect to the base element (3); - a vibration generator unit (15) for generating reference accelerations on the rotary table (5); a vibration detection unit (17) for detecting reference accelerations and reference displacements of the rotary table (5) which are actually present on the rotary table (5); a control unit which is configured and designed to actuate the vibration generator unit (15) for generating reference accelerations and at the same time the motor (11) for rotating the rotary table (5) with respect to the base element (3); wherein the receptacle (7) can be tilted with respect to the rotary table (5) such that an orientation of the inertial sensor (1) can be changed together with an orientation of the reference sensor unit (9) with respect to the axis of rotation of the rotary table (5) without the inertial sensor (1) having to be removed from the receptacle (7) for its change of orientation.The apparatus according to claim 1, wherein the vibration detection unit (17) includes a plurality of acceleration sensors, wherein measurement directions of the acceleration sensors each have an angle to a designated direction of the reference accelerations.The apparatus of claim 2, wherein the measurement directions are aligned along a cone.Device according to one of the preceding claims, further comprising a temperature control device for setting a desired temperature at the inertial sensor (1) when the latter is accommodated in the receptacle (7).Method for carrying out tests for the characterization and / or calibration of an inertial sensor (1), wherein a device is used which has a stationary base element (3) and a rotary table (5) rotatably mounted on the base element (3), wherein the rotary table (5) has a receptacle (7) for the inertial sensor (1) and for a reference sensor unit (9), and the device has a motor (11), connected to the rotary table (5), for rotating the rotary table (5) with respect to the base element (3) about an axis of rotation, a reference rotary cutter (13) for determining a current rotational position and rotational rate of the rotary table (5) with respect to the base element (3), a vibration generator unit (15) for generating reference accelerations on the rotary table (5), a vibration detection unit (17) for detecting reference accelerations and reference displacements of the rotary table (5) which are actually present on the rotary table (5), and a control unit which controls the vibration generating unit (15) for generating reference accelerations and at the same time controls the motor (11) for rotating the rotary table (5) with respect to the base element (3), and wherein the receptacle (7) is tiltable on the rotary table (5); wherein an orientation of the inertial sensor (1) is changed together with an orientation of the reference sensor unit (9) with respect to the axis of rotation of the rotary table (5) without removing the inertial sensor (1) from the receptacle (7) and without removing the reference sensor unit (9) by tilting the receptacle (7), and wherein sensor signals of the inertial sensor (1) arranged on the receptacle (7) are read out and are compared with reference signals from at least the reference sensor unit (9).Method according to Claim 5, wherein a rotation sensor or an acceleration sensor is used as the inertial sensor (1).Method according to claim 6, wherein for a rotation sensor as the inertial sensor (1) the sensor signals of the inertial sensor (1) are read out for at least two different alignments of the receptacle (7) relative to the rotation table (5), respectively under vibrations generated by the vibration generating unit (15) and under the rotation of the rotation table (5) and compared with reference signals from at least the reference sensor unit (9).Method according to claim 6, wherein for an acceleration sensor as the inertial sensor (1), the sensor signals of the inertial sensor (1) are read out for at least two different alignments of the receptacle (7) relative to the intended direction of the reference accelerations, which are compared with reference signals at least from the reference sensor unit (9) by different possible combinations of the alignment between the receptacle (7) with respect to the rotary table (5), the angular position of the rotary table (5) with respect to the base element (3) and the alignment of the vibration generator unit (15), respectively under vibrations generated by the vibration generator unit (15) and optionally under rotation of the rotary table (5).Method according to one of Claims 5 to 8, wherein a sensor fusion of the signals of the reference sensor unit (9), the vibration detection unit (17) and the reference rotation meter (13) is carried out, and the result of the sensor fusion is used to determine reference signals, wherein the reference signals are compared with the sensor signals of the inertial sensor (1).Method according to claim 9, wherein an orientation error and a bias of the signals of the reference sensor unit (9) and / or of the vibration detection unit (17) and / or of the reference rotation meter (13), or of the reference signals, are estimated.

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