Digital level

Abstract

This digital level (100) comprises: an inclination angle sensor mechanism (1) that detects the inclination angle of an object; a rotary table (2) that supports the inclination angle sensor mechanism; a rotary shaft (3) that rotates the rotary table; and a control device (6) that controls the rotation of the rotary shaft. The control device (6) includes: a rotation control unit (61) that performs control so as to position the rotary shaft at an arbitrary rotation position; an acquisition unit (62) that acquires a first inclination angle detected by the inclination angle sensor mechanism when the rotary shaft is positioned at a first rotation position by the rotation control unit, and a second inclination angle detected by the inclination angle sensor mechanism when the rotary shaft is positioned at a second rotation position different from the first rotation position; and a horizontal accuracy calculation unit (63) that calculates, on the basis of the first inclination angle and the second inclination angle acquired by the acquisition unit, a horizontal accuracy included in the detection result of the inclination angle sensor mechanism.

Description

Digital Level

[0001] The present invention relates to a digital level that outputs the measured inclination angle of a target object as a digital value.

[0002] As a device for measuring the inclination angle of a target object, a digital level is known. The digital level outputs the inclination angle of the target object as a numerical value. Digital levels are used in cases such as when a specific numerical value of an inclination angle is desired to be obtained, or when the measured inclination angle is used as data for calculations and the like. The digital level stores an inclination angle of 0 degrees indicating level (zero point) as a reference value, and measures the inclination angle of the target object based on a difference from the reference value. This zero point is set to match the horizontal, for example at the time of manufacturing, but may deviate from horizontal due to temperature changes in the usage environment of the level, aging, and other factors. Therefore, a user needs to check the fluctuation of the zero point (leveling accuracy) before measuring an inclination angle, and calibrate the level as necessary. Calibration of a level is disclosed, for example, in Patent Document 1.

[0003] The digital level disclosed in Patent Document 1 measures an inclination angle at a certain measurement position, then rotates the level 180 degrees from that position and measures the inclination angle at another measurement position. The digital level uses these two inclination angles to check the fluctuation of the zero point of the level (leveling accuracy). The digital level is attached to the outer peripheral surface of a cylindrical body by an attachment means such as a screw. This allows the digital level to reverse its attachment position by 180 degrees on the cylindrical body.

[0004] Japanese Patent Laid-Open No. 2009-092526

[0005] According to the digital level of Patent Document 1, the leveling accuracy of the level can be checked, and the level can be calibrated as necessary. However, Patent Document 1 does not disclose a specific method for rotating the digital level by 180 degrees. Based on common technical knowledge, it is considered that in Patent Document 1, the digital level is rotated 180 degrees manually. Manually checking the leveling accuracy every time the level is used reduces work efficiency. In addition, for example, when a level is built into another machine, it may be difficult for human hands to reach the level. In this case, it becomes difficult to check the leveling accuracy.

[0006] The objective of this invention is to enable easy verification of horizontal accuracy in a digital level.

[0007] The digital level of the present invention is configured to automatically rotate an inclination angle sensor mechanism that measures the inclination angle of an object. At at least two arbitrary rotation positions, the inclination angle sensor mechanism measures the inclination angle of the object. The digital level calculates the horizontal accuracy of the inclination angle sensor mechanism based on the two measured inclination angles.

[0008] The digital level of the present invention allows for automatic verification of the horizontal accuracy of the tilt angle sensor mechanism without human intervention. Therefore, this digital level makes it easy to verify the horizontal accuracy of the tilt angle sensor mechanism.

[0009] This is a perspective view showing the configuration of a digital level. This is a functional block diagram showing the configuration of the control device in the digital level.

[0010] The embodiments of the present invention will be described below with reference to the drawings. First, the configuration of the digital level of this embodiment will be described.

[0011] Figure 1 is a perspective view showing the configuration of a digital level. The digital level 100 comprises a tilt angle sensor mechanism 1, a rotary table 2, a rotary shaft 3, a base 4, and a posture sensor mechanism 5.

[0012] The tilt angle sensor mechanism 1 measures the tilt angle (horizontalness) of the object T. The type of tilt angle sensor mechanism 1 is not particularly limited. Examples of tilt angle sensor mechanisms 1 include bubble level type, optical type, ultrasonic type, gyro sensor type, etc. The tilt angle sensor mechanism 1 may measure the tilt angle in one axis direction or in multiple axis directions. The tilt angle sensor mechanism 1 is housed in a housing 11. The housing 11 may include a display that outputs the measured tilt angle. Note that the tilt angle measured by the tilt angle sensor mechanism 1 is not limited to being displayed on the display. The tilt angle measured by the tilt angle sensor mechanism 1 may be output to another device by wired or wireless communication, etc. The tilt angle sensor mechanism 1 is placed on the rotary table 2 via the housing 11.

[0013] The rotary table 2 has a disc shape. However, the shape of the rotary table 2 is not particularly limited. The rotary table 2 may be a polygonal plate or the like. The rotary table 2 includes a mounting surface 21 on which the tilt angle sensor mechanism 1 (housing 11) is placed. The mounting surface 21 is flat. The mounting surface 21 is designed to be parallel to the surface of the object T on which the tilt angle is to be measured. However, the mounting surface 21 does not have to be strictly flat. Also, the mounting surface 21 does not have to be strictly parallel to the measuring surface of the object T. This is because the parallelism between the mounting surface 21 and the measuring surface of the object T can be loosened, for example, by calibration during the manufacturing of the digital level. The mounting surface 21 is in close contact with the bottom surface (detection surface) of the housing 11. The rotary table 2 is fixed to the tilt angle sensor mechanism 1 (housing 11) via a fixing member. The fixing member is not particularly limited. The fixing member may be, for example, adhesive, screws, etc.

[0014] The rotating shaft 3 supports the rotary table 2. More specifically, the rotating shaft 3 has a cylindrical shape. The rotating shaft 3 extends in the direction normal to the mounting surface 21 of the rotary table 2. However, the rotating shaft 3 does not have to extend strictly in the direction normal to the mounting surface 21. This is because the perpendicularity of the rotating shaft 3 to the mounting surface 21 can be loosened, for example, by calibration during the manufacture of the digital level. Also, the shape of the rotating shaft 3 is not particularly limited. The rotating shaft 3 only needs to be able to rotate the rotary table 2. One end of the rotating shaft 3 is connected to the rotary table 2. The other end of the rotating shaft 3 is connected to a drive device (not shown). The drive device is not particularly limited. The drive device is, for example, a motor. The drive device rotates the rotary table 2 by rotating the rotating shaft 3. That is, the central axis of the rotating shaft 3 becomes the rotational central axis of the rotary table 2 (tilt angle sensor mechanism 1). The rotating shaft 3 rotates substantially in a plane parallel to the surface of the object T for which the tilt angle sensor mechanism 1 measures the tilt angle. The rotational position of the rotating shaft 3 is detected by a rotary encoder (not shown). The rotating shaft 3 may also have a sliding function that allows it to slide in the direction of its central axis, and a holding function that maintains its position in the direction of its central axis. For example, the rotating shaft 3 slides before rotation and rotates at the slid position. After rotation, the rotating shaft 3 returns to its original position. This helps to suppress wear of the rotating shaft 3 due to rotation. Furthermore, if the drive device is a stepping motor, for example, the rotational position can be determined to some extent based on the input pulse. In this case, a rotary encoder may not be necessary.

[0015] The base 4 supports the rotating shaft 3. The base 4 is provided to support the end of the rotating shaft 3 opposite to the end connected to the rotary table 2. A bearing or the like is interposed between the base 4 and the rotating shaft 3. That is, the base 4 is configured not to rotate in conjunction with the rotation of the rotating shaft 3. The base 4 has a generally disc shape. However, the shape of the base 4 is not particularly limited. The base 4 is configured to overlap the rotary table 2 when viewed in the direction of the central axis of the rotating shaft 3. The bottom surface of the base 4 is flat. The bottom surface of the base 4 is in close contact with the surface of the object T. Note that the entire bottom surface of the base 4 does not have to be flat. At least the portion of the bottom surface of the base 4 that is in contact with the object T is configured to be flat.

[0016] The attitude sensor mechanism 5 includes a plurality of displacement sensors 51-54. The plurality of displacement sensors 51-54 are mounted on the back surface of the rotary table 2 (the surface opposite to the mounting surface 21). The plurality of displacement sensors 51-54 are arranged at equal intervals around the central axis of the rotation shaft 3. The plurality of displacement sensors 51-54 rotate around the rotation shaft 3 in conjunction with the rotation shaft 3. The plurality of displacement sensors 51-54 are provided at a predetermined distance from the base 4. Each of the plurality of displacement sensors 51-54 measures the predetermined distance. In this embodiment, the plurality of displacement sensors 51-54 are mounted on the rotary table 2, but they may also be mounted on the base 4. In this case, each of the plurality of displacement sensors 51-54 is provided at a predetermined distance from the rotary table 2, and the distance is measured.

[0017] The digital level 100 further includes a control device 6 that controls the rotation of the rotation axis 3. The control device 6 is composed of a computer including a processor. The control device 6 performs various processes by executing a computer program stored on a recording medium. In this embodiment, the control device 6 is provided separately from the tilt angle sensor mechanism 1 (housing 11). However, the control device 6 may be built into the housing 11. The control device 6 is electrically connected to the tilt angle sensor mechanism 1, the attitude sensor mechanism 5, and the rotation axis 3. The connection method may be wired or wireless.

[0018] Next, the fluctuation in the horizontal accuracy of the tilt angle sensor mechanism 1 and the method for confirming it will be explained. The horizontal accuracy of the tilt angle sensor mechanism 1 may fluctuate due to temperature changes in the operating environment, aging, etc. Here, we assume that the horizontal accuracy of the tilt angle sensor mechanism 1 is off by +1 degree from the accurate value. We also assume that the tilt angle of the object T is +10 degrees. In this case, when the tilt angle sensor mechanism 1 measures the tilt angle of the object T while the rotation axis 3 is in a certain rotation position, the tilt angle sensor mechanism 1 outputs the tilt angle of the object T as +11 degrees (= 10 degrees + 1 degree). After that, the tilt angle sensor mechanism 1 is rotated 180 degrees from the current rotation position. When the tilt angle sensor mechanism 1 measures the tilt angle of the object at this rotation position, the tilt angle sensor mechanism 1 outputs the tilt angle of the object T as -9 degrees (-10 degrees + 1 degree). Dividing the sum of the two outputted tilt angles by 2 gives the fluctuation value of the horizontal accuracy inherent in the tilt angle sensor mechanism 1 (+1 degree). Furthermore, dividing the difference between the two output inclination angles by 2 gives the inclination angle of object T (+10 degrees).

[0019] Thus, the horizontal accuracy of the tilt angle sensor mechanism 1 is determined based on two tilt angles measured in different orientations. The digital level 100 of this embodiment is configured to perform this automatically. Specifically, with the rotation axis 3 positioned at a certain rotation position (first rotation position), the tilt angle sensor mechanism 1 measures the tilt angle of the object T (first tilt angle). Next, the drive device rotates the rotation axis 3 180 degrees around the central axis of the rotation axis 3 from the first rotation position to a rotation position (second rotation position). In this state, the tilt angle sensor mechanism 1 measures the tilt angle of the object T (second tilt angle). The control device 6 calculates the horizontal accuracy of the tilt angle sensor mechanism 1 based on the measured first and second tilt angles. The control device 6 also calculates the tilt angle of the object T.

[0020] Next, the rotational accuracy (shaft runout) of the rotating shaft 3 will be explained. As described above, in the digital level 100 of this embodiment, the rotating shaft 3 is rotated by a drive device, and the horizontal accuracy of the tilt angle sensor mechanism 1 is automatically determined. The above explanation assumes that the rotating shaft 3 rotates accurately according to the design value. However, in reality, the rotating shaft 3 contains mechanical errors such as eccentricity and tilting of its central axis. For example, the state shown in Figure 1 is the state in which the rotating shaft 3 is positioned at the first rotation position. If the rotating shaft 3 is tilted in the direction from position P3 to position P1, the tilt of the rotating shaft 3 will affect the tilt of the tilt angle sensor mechanism 1. As a result, the measurement accuracy of the tilt angle sensor mechanism 1 at the first rotation position will decrease. This decrease in the measurement accuracy of the tilt angle sensor mechanism 1 due to the tilt of the rotating shaft 3 is also true for the measurement of the tilt angle at the second rotation position, which is 180 degrees rotated from the first rotation position. Therefore, it is better if the trajectory of the rotating shaft 3 when it is rotated around its central axis is as close to the design value as possible. In other words, the smaller the runout of the rotating shaft 3, the better.

[0021] Generally, mechanical errors in a rotating shaft can be suppressed to some extent by bearings, etc. However, since this type of mechanical error depends on the performance (precision) of the bearings, expensive bearings may be required depending on the specifications of the digital level 100. In addition, shaft runout due to mechanical errors may vary from unit to unit when digital levels are mass-produced. Therefore, it is difficult to calibrate multiple mass-produced digital levels to a uniform value. Furthermore, shaft runout tends to change over time, depending on the frequency of use of the equipment. Even if the variation in shaft runout between units is suppressed, it is difficult to suppress or predict the change in variation over time. As a result, the rotational precision of the rotating shaft 3 will affect the horizontal precision of the tilt angle sensor mechanism 1, which is determined by automatically rotating the rotating shaft 3.

[0022] Therefore, the digital level 100 of this embodiment is characterized by detecting, rather than suppressing, the aforementioned axial runout. The digital level 100 detects the orientation of the rotation axis 3 using the orientation sensor mechanism 5 and calculates the rotational accuracy of the rotation axis 3 based on the detected orientation of the rotation axis 3.

[0023] Specifically, with the rotation axis 3 positioned at a rotational position (for example, a first rotational position), the multiple displacement sensors 51-54 each measure the distance between themselves and the base 4. For example, the state shown in Figure 1 is the state in which the rotation axis 3 is positioned at the first rotational position. In this case, displacement sensor 51 measures the distance between itself and the base 4 at position P1. Displacement sensor 52 measures the distance between itself and the base 4 at position P2, which is 90 degrees from position P1 around the central axis of the rotation axis 3. Similarly, displacement sensor 53 measures the distance at position P3, which is 180 degrees from position P1, and displacement sensor 54 measures the distance at position P4, which is 270 degrees from position P1. Let's assume that the measurement results of displacement sensor 52 and displacement sensor 54 are the same, and the measurement result of displacement sensor 51 is smaller than the measurement result of displacement sensor 53. In this case, the rotation axis 3 is tilted from the design central axis towards position P1. In this way, the digital level 100 determines the orientation of the rotation axis 3 when the rotation axis 3 is positioned at the first rotation position.

[0024] Next, the drive unit rotates the rotation shaft 3 by 180 degrees to a second rotation position. In this state, as with the first rotation position, the multiple displacement sensors 51-54 each measure the distance between themselves and the base 4. This allows the digital level 100 to determine the orientation of the rotation shaft 3 when it is positioned at the second rotation position. Based on the determined orientation of the rotation shaft 3 at the first rotation position and the orientation of the rotation shaft 3 at the second rotation position, the digital level 100 can determine the deviation from the design center axis (rotation accuracy) when the rotation shaft 3 rotates. The digital level 100 calculates the horizontal accuracy of the tilt angle sensor mechanism 1, taking into account the determined rotation accuracy.

[0025] Next, we will explain how to calculate the horizontal accuracy of the tilt angle sensor mechanism 1 and the rotational accuracy of the rotation axis 3.

[0026] Figure 2 is a functional block diagram showing the configuration of the control device in a digital level. The control device 6 includes a rotation control unit 61, an acquisition unit 62, a horizontal accuracy calculation unit 63, a rotation accuracy calculation unit 64, an inclination angle correction unit 65, and a storage unit 66.

[0027] The rotation control unit 61 controls the rotation shaft 3 to be positioned at an arbitrary rotational position. For example, when the power to the digital level 100 is turned on, the rotation control unit 61 starts processing to calculate the horizontal accuracy of the tilt angle sensor mechanism 1. That is, the rotation control unit 61 sends a command to the drive device to rotate the rotation shaft 3. The rotation control unit 61 may also start processing in response to a user request sent via the control panel or the like.

[0028] The drive unit rotates the rotating shaft 3 upon receiving a command from the rotation control unit 61. The rotational position of the rotating shaft 3 is detected by the rotation encoder 7. When the rotating shaft 3 reaches the first rotational position, the rotation encoder 7 notifies the rotation control unit 61 of this fact. Upon receiving notification from the rotation control unit 61, the rotation control unit 61 stops the drive unit. In other words, the rotation control unit 61 positions the rotating shaft 3 at the first rotational position. The rotation control unit 61 may set the rotational position of the rotating shaft 3 at the time the digital level 100 is powered on as the first rotational position, or it may set a position different from the rotational position of the rotating shaft 3 at the time the power is powered on as the first rotational position. Subsequently, the rotation control unit 61 sends a command to the tilt angle sensor mechanism 1 to measure the tilt angle of the object. The rotation control unit 61 also sends a command to the attitude sensor mechanism 5 to measure the distance (attitude of the rotating shaft) provided between the attitude sensor mechanism 5 and the base 4.

[0029] When the tilt angle sensor mechanism 1 receives a command from the rotation control unit 61, it measures the tilt angle of the object at the first rotation position (first tilt angle). The tilt angle sensor mechanism 1 sends the measured first tilt angle to the acquisition unit 62. Also, when the attitude sensor mechanism 5 receives a command from the rotation control unit 61, it measures the distance between the attitude sensor mechanism 5 and the base 4 at the first rotation position. The attitude sensor mechanism 5 sends the measured distance to the acquisition unit 62.

[0030] The acquisition unit 62 stores the first tilt angle acquired from the tilt angle sensor mechanism 1 in the storage unit 66. Subsequently, the acquisition unit 62 notifies the rotation control unit 61 that the first tilt angle has been stored in the storage unit 66. Upon receiving notification from the acquisition unit 62 that the first tilt angle has been stored in the storage unit 66, the rotation control unit 61 sends a command to the drive unit to rotate the rotation shaft 3 again. The acquisition unit 62 also stores the distance between the attitude sensor mechanism 5 and the base 4 at the first rotation position (attitude of the rotation shaft 3), acquired from the attitude sensor mechanism 5, in the storage unit 66.

[0031] When the drive unit receives a command from the rotation control unit 61, it rotates the rotating shaft 3, which is positioned at the first rotation position. When the rotation encoder 7 reaches the second rotation position, which is 180 degrees rotated from the first rotation position, it notifies the rotation control unit 61 of this fact. Upon receiving the notification from the rotation control unit 61, the rotation control unit 61 stops the drive unit. That is, the rotation control unit 61 positions the rotating shaft 3 at the second rotation position. Subsequently, the rotation control unit 61 sends a command to the tilt angle sensor mechanism 1 to measure the tilt angle of the object. The rotation control unit 61 also sends a command to the attitude sensor mechanism 5 to measure the distance (attitude of the rotating shaft) provided between the attitude sensor mechanism 5 and the base 4 at the second rotation position.

[0032] When the tilt angle sensor mechanism 1 receives a command from the rotation control unit 61, it measures the tilt angle of the object at the second rotation position (second tilt angle). The tilt angle sensor mechanism 1 sends the measured second tilt angle to the acquisition unit 62. The attitude sensor mechanism 5 sends the measured distance between the attitude sensor mechanism 5 and the base 4 to the acquisition unit 62.

[0033] The acquisition unit 62 stores the second tilt angle acquired from the tilt angle sensor mechanism 1 in the storage unit 66. Subsequently, the acquisition unit 62 notifies the horizontal accuracy calculation unit 63 that the second tilt angle has been stored in the storage unit 66. The acquisition unit 62 also stores the distance (attitude of the rotation axis) between the attitude sensor mechanism 5 and the base 4 at the second rotation position, acquired from the attitude sensor mechanism 5, in the storage unit 66. Subsequently, the acquisition unit 62 notifies the rotation accuracy calculation unit 64 that the distance between the attitude sensor mechanism 5 and the base 4 at the second rotation position has been stored in the storage unit 66.

[0034] When the rotation accuracy calculation unit 64 receives notification from the acquisition unit 62, it acquires information regarding the orientation of the rotation axis 3 at a first rotation position and information regarding the orientation of the rotation axis 3 at a second rotation position from the storage unit 66. Based on the information regarding the orientation of the rotation axis 3 at the first rotation position and the information regarding the orientation of the rotation axis 3 at the second rotation position, the rotation accuracy calculation unit 64 calculates the rotation accuracy of the rotation axis 3. The rotation accuracy is the deviation from the design value when the rotation axis 3 rotates. The rotation accuracy indicates the degree to which the rotation axis 3 affects the measurement results of the tilt angle sensor mechanism 1. The rotation accuracy calculation unit 64 stores the calculated rotation accuracy in the storage unit 66. Subsequently, the rotation accuracy calculation unit 64 notifies the horizontal accuracy calculation unit 63 that the rotation accuracy has been stored in the storage unit 66.

[0035] When the horizontal accuracy calculation unit 63 receives notification from the rotation accuracy calculation unit 64, it obtains information regarding the rotation accuracy of the rotation shaft 3 from the storage unit 66. Also, when the horizontal accuracy calculation unit 63 receives notification from the acquisition unit 62 that the second inclination angle has been stored in the storage unit 66, it obtains information regarding the first inclination angle and information regarding the second inclination angle from the storage unit 66. Based on the acquired rotation accuracy, the first inclination angle, and the second inclination angle, the horizontal accuracy calculation unit 63 calculates the horizontal accuracy included in the output of the inclination angle sensor mechanism 1. More specifically, the horizontal accuracy calculation unit 63 takes the value obtained by subtracting the error due to rotation accuracy from the acquired first inclination angle as the corrected first inclination angle. The horizontal accuracy calculation unit 63 takes the value obtained by subtracting the error due to rotation accuracy from the acquired second inclination angle as the corrected second inclination angle. The horizontal accuracy calculation unit 63 calculates the horizontal accuracy based on the corrected first inclination angle and the corrected second inclination angle. In other words, the horizontal accuracy calculation unit 63 calculates the horizontal accuracy by taking into account the rotation accuracy of the rotating shaft 3 calculated by the rotation accuracy calculation unit 64. The horizontal accuracy calculation unit 63 stores the horizontal accuracy calculated taking into account the rotation accuracy in the storage unit 66. After that, the horizontal accuracy calculation unit 63 notifies the tilt angle correction unit 65 that the horizontal accuracy has been stored in the storage unit 66.

[0036] When the tilt angle correction unit 65 receives notification from the horizontal accuracy calculation unit 63, it obtains the horizontal accuracy calculated from the storage unit 66, taking into account the rotation accuracy. Based on the rotation accuracy, horizontal accuracy, and the first and second tilt angles obtained at that time, the tilt angle correction unit 65 calculates the corrected tilt angle of the measuring surface of the object T.

[0037] As described above, the digital level 100 of this embodiment can automatically and quickly calculate the horizontal accuracy of the tilt angle sensor mechanism 1. Therefore, the digital level 100 makes it easy to check the horizontal accuracy of the tilt angle sensor mechanism 1. In particular, the digital level 100 of this embodiment is effective when the digital level is built into another machine or placed in a location that is difficult for a person to reach.

[0038] Furthermore, the digital level 100 can automatically calculate the rotational accuracy of the rotating shaft 3 that rotates the tilt angle sensor mechanism 1. Even if the rotational accuracy of the rotating shaft 3 is not very high, the digital level 100 can calculate the horizontal accuracy of the tilt angle sensor mechanism 1, excluding errors caused by the rotational accuracy. Therefore, the tilt angle (horizontalness) of the object T can be measured with high precision using the digital level 100.

[0039] The digital level 100 of this embodiment has been described above. The embodiment described above is merely an example. The present invention is not to be interpreted in any way as being limited by the embodiment described above.

[0040] The above description described a configuration in which the control device 6 calculates the horizontal accuracy of the tilt angle sensor mechanism 1 by taking into account the rotation accuracy of the rotating shaft 3. However, if it is not necessary to consider the rotation accuracy of the rotating shaft 3, or if the rotation accuracy is known in advance, the control device 6 may calculate the horizontal accuracy of the tilt angle sensor mechanism 1 without taking into account the rotation accuracy of the rotating shaft 3. In other words, the control device 6 does not need to include a rotation accuracy calculation unit 64.

[0041] The above description described a configuration in which the control device 6 includes a tilt angle correction unit 65 that corrects the tilt angle output by the tilt angle sensor mechanism 1. However, in cases where, for example, only the horizontal accuracy of the tilt angle sensor mechanism 1 is to be checked, or when the output tilt angle is to be corrected separately, the control device 6 does not need to include the tilt angle correction unit 65.

[0042] In the above description, when checking the horizontal accuracy of the tilt angle sensor mechanism 1, the digital level 100 positions the rotation axis 3 at a first rotation position and a second rotation position and measures the tilt angle at each rotation position. However, the digital level 100 may position the rotation axis 3 at two or more rotation positions and measure the tilt angle at each rotation position. By measuring the tilt angle at more rotation positions, the digital level 100 can calculate the horizontal accuracy with higher precision. Preferably, the digital level 100 measures the tilt angle at each of a plurality of rotation positions obtained by dividing 360 degrees in the rotation direction of the rotation axis 3 into N divisions. Here, N is preferably 3 or more, but N may be 2.

[0043] In other words, the above explanation described the case where the rotation axis 3 is positioned at a first rotation position and a second rotation position rotated 180 degrees from the first rotation position. However, the second rotation position does not have to be rotated 180 degrees from the first rotation position. The second rotation position may be rotated by any angle from the first rotation position. For example, suppose the second rotation position is rotated 90 degrees from the first rotation position. In this case, the inclination angle measured at the second rotation position may be corrected by calculation to obtain an inclination angle that is effectively measured at a position rotated 180 degrees from the first rotation position.

[0044] In the above description, a case has been described where the tilt angle sensor mechanism 1 is a two-axis digital level that measures two-axis tilt angles. However, the digital level may be a single-axis digital level, or may be a digital level with three or more axes. When the tilt angle sensor mechanism 1 measures a tilt angle on M axes (M is 1 or more), the attitude sensor mechanism 5 preferably includes M or more displacement sensors. With such a configuration, when the rotation shaft 3 is positioned at a certain rotational position, each of the M or more displacement sensors can measure the distance between itself and the base 4 at a position on the corresponding axis. That is, with such a configuration, the distance between the displacement sensor and the base 4 at positions on each axis can be measured at one time.

[0045] The timing at which the digital level 100 calculates the horizontal accuracy of the tilt angle sensor mechanism 1 is not particularly limited. For example, the digital level 100 calculates the horizontal accuracy of the tilt angle sensor mechanism 1 when the device is powered on. The digital level 100 may calculate the horizontal accuracy of the tilt angle sensor mechanism 1 in accordance with a user operation. The digital level 100 may calculate the horizontal accuracy of the tilt angle sensor mechanism 1 regularly or irregularly. Note that the digital level 100 may hold, as an initial value, the horizontal accuracy of the tilt angle sensor mechanism 1 calculated when the device is powered on or in accordance with a user operation. In this case, after calculating the horizontal accuracy that is the initial value, the digital level 100 may correct the tilt angle output by the tilt angle sensor mechanism based on the initial value. With such a configuration, even if the calculation accuracy of horizontal accuracy changes due to aging, the tilt angle can be corrected with high accuracy.

[0046] In the above description, a case has been described where the control device 6 corrects the horizontal accuracy by directly using the rotation accuracy of the rotating shaft 3 calculated using the attitude sensor mechanism 5. However, the control device 6 may correct the calculated rotation accuracy of the rotating shaft 3, and correct the horizontal accuracy by using the corrected rotation accuracy. In this case, the control device 6 acquires calibration data of the rotation accuracy in advance. The calibration data of the rotation accuracy is created in advance by using, for example, another inclination angle reference device or the like. The calibration data of the rotation accuracy is created, for example, when manufacturing the digital level 100. For example, if the measurement accuracy of the attitude sensor mechanism 5 changes over time, the rotation accuracy calculated in accordance therewith also changes. If the control device 6 holds the calibration data, it can correct the changed rotation accuracy based on the calibration data. Therefore, the rotation accuracy and consequently the horizontal accuracy of the inclination angle sensor mechanism 1 can be calculated with high accuracy without depending on the deviation from the design value of the rotating shaft 3 (processing accuracy and assembly accuracy of the rotating shaft 3).

[0047] In the above description, a configuration has been described in which the attitude sensor mechanism 5 includes four displacement sensors 51 to 54 provided at 90-degree intervals around the rotating shaft 3. However, the number of displacement sensors is not limited to four, and the attitude sensor mechanism 5 only needs to include at least one displacement sensor. In addition, when the attitude sensor mechanism 5 includes a plurality of displacement sensors, the plurality of displacement sensors may be provided at equal intervals around the rotating shaft 3, or may be provided at unequal intervals.

[0048] When the attitude sensor mechanism 5 includes a plurality of displacement sensors, the control device 6 may monitor the output of each displacement sensor. For example, each of the plurality of displacement sensors measures the distance between itself and the base 4 at the same position. The control device 6 compares the measurement results of each displacement sensor and monitors the fluctuation of the output of each displacement sensor. When the control device 6 determines that there is a deteriorated displacement sensor among the plurality of displacement sensors, it is configured to ignore the output of the deteriorated displacement sensor or output an alarm. The control device 6 determines the deterioration of each displacement sensor based on, for example, a preset threshold value. With such a configuration, noise can be removed in the calculation of the rotation accuracy of the rotating shaft 3 using the displacement sensor.

[0049] The above description describes the case where, when the rotating shaft 3 is positioned at a certain rotational position, both the measurement of the tilt angle by the tilt angle sensor mechanism 1 (calculation of horizontal accuracy) and the measurement of the distance to the base 4 by the attitude sensor mechanism 5 (calculation of rotational accuracy) are performed. However, the calculation of horizontal accuracy and the calculation of rotational accuracy may be performed separately. It is desirable that the calculation of horizontal accuracy and the calculation of rotational accuracy be performed at the same rotational position to improve the accuracy of the calculation results. However, if the rotational accuracy of the rotating shaft 3, the rotational position, and the measured tilt angle are reproducible, the calculation of horizontal accuracy and the calculation of rotational accuracy may be performed at different rotational positions.

[0050] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of equivalents of the claims are intended.

[0051] This application is based on Japanese Patent Application No. 2025-052226, filed with the Japan Patent Office on 26 March 2025, the entire contents of which are incorporated herein by reference.

[0052] 100 Digital level, 1 Inclination angle sensor mechanism, 2 Rotating table, 21 Mounting surface, 3 Rotating axis, 4 Base, 5 Attitude sensor mechanism, 51-54 Displacement sensor, 6 Control device, 61 Rotation control unit, 62 Acquisition unit, 63 Horizontal accuracy calculation unit, 64 Rotation accuracy calculation unit, 65 Inclination angle correction unit, 66 Memory unit, T Object.

Claims

1. A digital level comprising: an inclination angle sensor mechanism for detecting the inclination angle of an object; a rotary table supporting the inclination angle sensor mechanism; a rotating shaft for rotating the rotary table; and a control device for controlling the rotation of the rotating shaft, wherein the control device includes: a rotation control unit for controlling the rotating shaft to position the rotating shaft at an arbitrary rotational position; an acquisition unit for acquiring a first inclination angle detected by the inclination angle sensor mechanism when the rotating shaft is positioned at a first rotational position by the rotation control unit, and a second inclination angle detected by the inclination angle sensor mechanism when the rotating shaft is positioned at a second rotational position different from the first rotational position; and a horizontal accuracy calculation unit for calculating the horizontal accuracy included in the detection result of the inclination angle sensor mechanism based on the first and second inclination angles acquired by the acquisition unit.

2. A digital level according to claim 1, further comprising: an attitude sensor mechanism for detecting the attitude of the rotating shaft, wherein the control device further includes a rotation accuracy calculation unit that calculates the rotation accuracy of the rotating shaft based on the attitude of the rotating shaft detected by the attitude sensor mechanism at the first rotation position and the second rotation position, respectively, and the horizontal accuracy calculation unit calculates the horizontal accuracy taking into account the rotation accuracy of the rotating shaft calculated by the rotation accuracy calculation unit.

3. A digital level according to claim 1, wherein the control device further includes a tilt angle correction unit that corrects the tilt angle detected by the tilt angle sensor mechanism based on the horizontal accuracy calculated by the horizontal accuracy calculation unit.

4. A digital level according to claim 1, wherein the rotation control unit controls the rotation axis to be positioned at each of a plurality of rotation positions obtained by dividing 360 degrees in the rotation direction of the rotation axis into N divisions, where N is 2 or more, the acquisition unit acquires the inclination angle detected by the inclination angle sensor mechanism at each of the plurality of rotation positions, and the horizontal accuracy calculation unit calculates the horizontal accuracy based on the N inclination angles acquired by the acquisition unit.

5. A digital level according to claim 2, wherein the digital level is capable of measuring the inclination angle of the M axis, M is 1 or more, the attitude sensor mechanism includes M or more displacement sensors, and when M is 2 or more, the M or more displacement sensors are arranged at 90-degree intervals or equal angle intervals in the rotation direction of the rotation axis to detect the attitude of the rotation axis.

6. A digital level according to claim 2, wherein the rotation accuracy calculation unit obtains the rotation accuracy of the rotation axis which has been calibrated in advance, and corrects the rotation accuracy of the rotation axis which has been calculated based on the rotation accuracy which has been calibrated in advance.

7. A digital level according to claim 2, wherein the attitude sensor mechanism includes a plurality of displacement sensors, and the rotation accuracy calculation unit monitors the output of each of the plurality of displacement sensors by comparing the detection results of each of the plurality of displacement sensors, and ignores the output of the deteriorated displacement sensor or outputs an alarm if there is a deteriorated displacement sensor.

8. A digital level according to claim 3, wherein the horizontal accuracy calculation unit calculates the horizontal accuracy as an initial value when the digital level is powered on or by operation by the user, and the tilt angle correction unit corrects the tilt angle detected by the tilt angle sensor mechanism based on the horizontal accuracy as an initial value after the horizontal accuracy as an initial value has been calculated.

9. A digital level according to claim 2, wherein the rotating shaft has a thrust-direction holding function and a thrust-direction sliding function, and slides in the thrust direction before rotation and returns to the original thrust-direction position after rotation positioning.

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