Torque sensor and screw tightening device equipped with same

Abstract

To provide a torque sensor with high torque detection accuracy.SOLUTION: A torque sensor 1 of the present invention comprises: sensors S1, S2 that send signals according to the rotation of a reference disc 10 and a comparison disc 20 arranged on a rotation shaft 5; a signal conversion unit 50 that converts output signals from the sensors S1, S2 into pulse signals; a phase difference calculation unit 60 that determines a calculated phase difference between a first pulse signal according to the reference disc 10 and a second pulse signal according to the comparison disc 20; and a torque operation unit 80 that calculates torque applied to the rotation shaft 5 based on the calculated phase difference. The phase difference calculation unit 60 is connected with a storage unit 70 that stores in advance, for every rotation angle of the reference disc 10, the zero-point correction phase difference between the first pulse signal and the second pulse signal while the rotation shaft 5 is rotated by one revolution at a constant speed without application of a load. The torque operation unit 80 corrects torque according to the rotation shaft 5 based on the zero-point correction phase difference, the current rotation angle of the reference disc 10, and the calculated phase difference.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a torque sensor that detects torque applied to a rotating shaft and a screw tightening device equipped with the torque sensor. [Background technology]

[0002] As disclosed in Patent Document 1, a conventional torque sensor includes a rotating shaft that rotates upon receiving a rotational force from a drive source, a reference disk that is arranged on the rotation input side of the rotating shaft and rotates integrally with the rotating shaft, a comparison disk that is arranged on the rotation output side of the rotating shaft and rotates integrally with the rotating shaft, and sensors that detect the rotation of the reference disk and comparison disk and output pulse signals related to the rotation.

[0003] The reference disk and the comparison disk both have magnetic poles arranged radially, and the sensor is configured to detect the magnetic poles of the rotating reference disk and comparison disk, convert them into pulse signals, and output them. The sensor is also connected to a processing means that takes in both pulse signals and calculates the torque applied to the rotating shaft based on the phase difference of the pulse signals. This allows the conventional torque sensor to have a relatively simple structure without mechanical contact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 63-161339 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional torque sensor, even if the rotating shaft is rotating without load, if the intervals between the magnetic poles of the reference disk and the comparison disk are not uniform as shown in Figures 3(a) and (b), the pulse signals related to the reference disk and the comparison disk output from the sensor do not match, resulting in a phase difference. This causes a problem in that the conventional torque sensor erroneously detects that torque is being applied to the rotating shaft even when the rotating shaft is rotating without load.

[0006] In addition, in the conventional torque sensor, even if the magnetic poles of the reference disk and the comparison disk are finished to have uniform spacing, when the reference disk and the comparison disk are attached to the rotating shaft, the axial centers of the reference disk and the comparison disk may not coincide and may be offset as shown in FIG. 4. If the axial centers of the reference disk and the comparison disk are offset in this manner, the above-mentioned phase difference occurs between the pulse signals of both disks when the rotating shaft is rotating without load. Therefore, the phase difference when torque is applied to the rotating shaft includes the above-mentioned phase difference when the rotating shaft is rotating without load, which causes a problem that accurate torque detection cannot be performed. [Means for solving the problem]

[0007] The present invention aims to provide a torque sensor that eliminates erroneous detection of torque during unloaded rotation of a rotating shaft and a screw fastening device equipped with the same, and includes a rotating shaft having a reference disk and a comparison disk arranged in the axial direction, a sensor that generates a signal in accordance with the rotation of the reference disk and the comparison disk, a signal conversion unit that converts the signal output from the sensor into a pulse signal, a phase difference calculation unit that takes in a first pulse signal related to the reference disk and a second pulse signal related to the comparison disk converted by the signal conversion unit and calculates the phase difference between the two as a calculated phase difference, and a phase difference calculation unit that calculates the calculated phase difference and the rotating shaft. and a torque calculation unit that calculates a torque applied to a rotating shaft from a coefficient calculated by the coefficient, wherein the phase difference calculation unit is connected to a memory unit that stores in advance a phase difference between the first pulse signal and the second pulse signal during one rotation at a constant speed under no-load rotation of the rotating shaft as a zero-point correction phase difference for each rotation angle of the reference disk, and the torque calculation unit is configured to correct and calculate the torque applied to the rotating shaft based on the zero-point correction phase difference for each rotation angle of the reference disk stored in the memory unit, the current rotation angle of the reference disk, and the calculated phase difference, and the memory unit stores For each given rotation angle , the zero-point correction phase difference is All around The present invention is characterized in that it stores information in a predetermined amount. Also, it is preferable that the sensor is an optical sensor. Effect of the Invention

[0008] The torque sensor and the screw tightening device equipped with the torque sensor according to the present invention correct the torque applied to the rotation torque based on the zero-point correction phase difference in the storage unit, the current rotation angle of the reference disk, and the calculated phase difference, so that torque detection can be performed with the phase difference between the reference disk and the comparison disk canceled under no-load conditions. This can eliminate problems caused by improper installation of the reference disk and the comparison disk as in the past, and has the advantage of ensuring high torque detection accuracy without having to strictly determine the installation position of the sensor in advance. In addition, the torque sensor and the screw tightening device equipped with the torque sensor according to the present invention are equipped with an optical sensor that detects the reference disk and the comparison disk, so that there is no need to attach a strain gauge to the rotating shaft, for example, and there is also the advantage of reducing the cost of manufacture. Moreover, the torque sensor and the screw tightening device according to the present invention store the zero-point correction phase difference in the range of every 0.002 degrees to every 0.01 degrees of the rotation angle of the reference disk, so that there is also the advantage of being able to appropriately eliminate torque detection errors due to the rotation angle of the rotating shaft and ensure sufficient torque detection accuracy for screw tightening work. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic explanatory diagram showing an example of a torque sensor according to the present invention. [Diagram 2] 1 is a schematic explanatory diagram showing an example of a screw fastening device according to the present invention; [Diagram 3] FIG. 1 is a schematic explanatory diagram showing an example in which a phase difference occurs in the pulse signals of a reference disk and a comparison disk when the reference disk and the comparison disk that form the basis of the pulse signal are overlapped in a simulated manner. (a) shows a state in which the polarity intervals of the reference disk and the comparison disk that form the basis of the pulse signal are not aligned, and (b) is an enlarged view of a key portion of (a). [Figure 4] FIG. 4 is a schematic explanatory diagram for illustrating a state in which a reference disc and a comparative disc are overlapped in a simulated manner, as in FIG. 3, and the axial centers of the reference disc and the comparative disc do not coincide with each other. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The torque sensor according to the present invention and a screw tightening device equipped with the same will be described with reference to Figures 1 to 4. First, the torque sensor 1 according to the present invention comprises a rotating shaft 5 extending in the axial direction, a reference disk 10 and a comparison disk 20 fixed to the rotating shaft 5 and arranged side by side in the axial direction so as to rotate integrally with the rotating shaft 5, sensors S1 and S2 that detect the reference disk 10 and the comparison disk 20 and send signals, and torque detection means 30 that detects the torque applied to the rotating shaft 5 based on the output signals of the sensors S1 and S2.

[0011] The rotating shaft 5 has a small diameter in its middle portion and large diameters at both ends, with the reference disk 10 fixed to one end and the comparison disk 20 fixed to the other end. A highly tough metal is selected for the rotating shaft 5, and heat treatment is performed to improve toughness and strength. By setting the middle portion to a small diameter, it is easily twisted when subjected to torque. The diameter of the rotating shaft 5 is appropriately set according to the torque detection capacity of the torque sensor 1, and the dimensions are preset so that the rotating shaft 5 elastically deforms within the elastic deformation range within the torque detection range.

[0012] The reference disk 10 and the comparison disk 20 have the same structure, and only the reference disk 10 will be described here. The reference disk 10 is a thin metal disk, and is provided with a number of notches 11 (21) arranged radially as shown in Figures 3 and 4. The notches 11 (21) are formed by cutting out a part of the metal so as to transmit the light emitted from the sensors S1 and S2.

[0013] As shown in Figures 1 and 2, the sensors S1 and S2 are arranged to detect the notches 11 and 12, respectively, and are so-called optical sensors configured to output an ON / OFF signal to the outside indicative of whether or not the notches 11 and 12 are detected.

[0014] The torque detection means 30 includes a signal conversion unit 50 that takes in ON and OFF signals output from the sensors S1 and S2, respectively, and converts them into a pulse signal; a phase difference calculation unit 60 that calculates a phase difference between a first pulse signal related to the sensor S1 and a second pulse signal related to the sensor S2 output from the signal conversion unit 50 as a calculated phase difference; a memory unit 70 that links and stores the calculated phase difference calculated by the phase difference calculation unit 60 and a reference angle, which is the rotation angle of the reference disk 10 corresponding to the calculated phase difference; and a torque calculation unit 80 that corrects and calculates the torque applied to the rotating shaft 5 based on the memory information linked and stored in the memory unit 70 and the calculated phase difference.

[0015] The signal conversion unit 50 includes a first pulse signal conversion unit 51 connected to the sensor S1 and a second pulse signal conversion unit 52 connected to the sensor S2. The first pulse signal conversion unit 51 and the second pulse signal conversion unit 52 are configured to convert the ON signal and the OFF signal output from the sensors S1 and S2, respectively, into the first pulse signal and the second pulse signal.

[0016] The phase difference calculation unit 60 calculates the calculated phase difference based on the first pulse signal and the second pulse signal, and transmits the calculated phase difference to the memory unit 70 for each rotation angle of the reference disk 10 that is preset.

[0017] The storage unit 70 is configured to store the calculated phase difference for each rotation angle of the reference disk 10 transmitted from the phase difference calculation unit 60 in association with each other, and to store this stored information in advance as a zero point correction value of the torque sensor 1. The storage unit 70 also stores a preset coefficient related to the elastic deformation of the rotating shaft 5. The zero point correction value is used to correct the error between the reference disk 10 and the comparison disk 20 during no-load rotation of the rotating shaft 5, and can ensure the accuracy of the detected torque even when the intervals between the notched portions 11 (21) are uneven as shown in Figs. 3(a), (b) and 4, or when the axial centers of the reference disk 10 and the comparison disk 20 are offset.

[0018] Specifically, the zero point correction value is data collected when the rotating shaft 5 is rotated once at a constant speed without applying a load in the torsional direction, and is composed of the rotation angle of the reference disk 10 and a calculated phase difference corresponding to the rotation angle. The rotation angle of the reference disk 10 is a value obtained by equally dividing 360 degrees and is preset, specifically, set in increments of 0.005 degrees.

[0019] The torque calculation unit 80 is connected to the phase difference calculation unit 60 and the storage unit 70, and is configured to calculate the torque applied to the rotating shaft 5. This torque calculation is performed in a state where a zero point correction value is stored in advance in the storage unit 70, and is performed based on the calculated phase difference output from the phase difference calculation unit 60, the coefficients stored in the storage unit 70, the rotation angle range of the reference disk 10 corresponding to the calculated phase difference, and the zero point correction value. In this way, the torque sensor 1 according to the present invention can cancel out the characteristics of the reference disk 10 and the comparison disk 20 during no-load rotation that have been collected in advance, and therefore makes it possible to accurately measure the torque applied to the rotating shaft 5.

[0020] Next, as shown in FIG. 2, a screw fastening device 90 according to the present invention equipped with the above-mentioned torque sensor 1 is composed of a motor M which imparts rotation to the rotating shaft 5, a connecting member 25 which connects the output shaft Ma of the motor M to the rotating shaft 5, a cover 26 which is arranged to cover the torque sensor 1 and to which the motor M can be attached on top, a bearing 27 which is arranged under the cover 26 and supports one end of the rotating shaft 5, and a motor control means 85 which connects the torque detection means 30 and the motor M and controls the rotational drive of the motor M.

[0021] The motor control means 85 is composed of a drive command unit 86 that issues commands to drive and stop the rotation of the motor M, a motor control unit 87 that is connected to the drive command unit 86 and the torque calculation unit 80, and a parameter storage unit 88 that is connected to the motor control unit 87 and stores parameters such as the rotation conditions of the motor M. The parameter storage unit 88 stores in advance a plurality of various parameters related to the rotation drive, such as the rotation speed of the output shaft Ma of the motor M and the fastening completion torque.

[0022] The motor control unit 87 is configured to be able to read out various parameters stored in the parameter storage unit 88, and is configured to be able to control the rotational drive of the motor M to the drive command unit 86 based on the parameters. The motor control unit 87 is also configured to be able to compare the detected torque applied to the rotating shaft 5 corrected by the torque calculation unit 80 with the fastening completion torque, and is configured to select a signal to be sent to the drive command unit 86 by determining whether the detected torque has reached the fastening completion torque.

[0023] The operation of the torque sensor 1 configured as above and the screw tightening device 90 equipped with the torque sensor 1 will be described. The screw tightening device 90 according to the present invention is used after first collecting data on the inherent error of the torque sensor 1, and this data collection is performed for the purpose of calibrating the error due to the rotation angle of the rotating shaft 5 of the torque sensor 1. This calibration is performed at a low set rotation speed of about 1 min^-1 to 5 min^-1 of the output shaft Ma of the motor M, and is completed by collecting the zero point correction value that links the rotation angle of the reference disk 10 and the calculated phase difference calculated by the phase difference calculation unit 60 according to the rotation angle for each of the preset rotation angle ranges until the rotating shaft 5 makes one rotation, and storing it in the storage unit 70.

[0024] This calibration makes it possible to clarify the calculated phase difference between the first pulse signal and the second pulse signal generated during no-load rotation, thereby making it possible to correct the error of the zero point due to the attachment of the reference disk 10 and the comparison disk 20, etc. Furthermore, since the calculated phase difference is linked to the rotation angle of the reference disk 10 when it is calculated, it is possible to appropriately correct the torque error for each rotation angle of the rotating shaft 5. Therefore, the screw fastening device 90 according to the present invention can perform torque measurement by canceling the error inherent to the torque sensor 1, so that the load torque can be correctly recognized as zero during no-load rotation, enabling accurate torque measurement.

[0025] In this embodiment, the reference disk 10 and the comparison disk 20 are thin metal disks, but may be cylinders having a predetermined thickness. Although the reference disk 10 and the comparison disk 20 are provided with the notches 11 and 21, the S poles and the N poles may be radially arranged alternately. In this case, the sensors S1 and S2 may be magnetic sensors (not shown) that detect the S poles and the N poles and output ON and OFF signals according to the polarity to the outside. Furthermore, the reference disk 10 and the comparison disk 20 have the same structure in this embodiment, but may have different structures, for example, the reference disk 10 is a thin disk and the comparison disk 20 is a cylinder. Furthermore, one of the sensors S1 and S2 may be an optical sensor and the other a magnetic sensor. Furthermore, in this embodiment, the zero point correction value is set every 0.005 degrees of the rotation angle of the reference disk 10, but it is not limited thereto, and may be set finer, for example, every 0.002 degrees, or coarser, for example, every 0.01 degrees, and may be set appropriately according to the allowable torque accuracy. In addition, in this embodiment, the cutout portion 11 (21) may be replaced with a depression or a groove formed to reflect the light emitted from the sensors S1 and S2, and the depression or groove may be formed by so-called etching. In this case, the sensor is configured to change the signal to be output based on the difference in the reflectance of the light irradiated to the depression or groove. Furthermore, in this embodiment, the rotating shaft 5 has a small diameter in the middle portion, but it is not limited thereto, and may be formed with a large diameter or the same diameter. In addition, the rotating shaft 5 is made of a metal with high toughness and is heat-treated, but if a material such as aluminum is selected, heat treatment may not be required. [Explanation of symbols]

[0026] 1 … Torque sensor 5 … Rotation axis 10 … Reference disc 20... Comparison disc 30 ... Torque detection means 50 ... Signal conversion section 60 ... Phase difference producing section 80 ... Torque calculation section 90 … Screw tightening device S1, S2 … Sensor

Claims

1. a torque sensor including a rotating shaft having a reference disk and a comparison disk arranged in an axial direction, a sensor that detects a plurality of notches radially provided on the reference disk and the comparison disk as the reference disk and the comparison disk rotate and generates a signal, a signal conversion unit that converts the signal output from the sensor into a pulse signal, a phase difference calculation unit that takes in a first pulse signal related to the reference disk and a second pulse signal related to the comparison disk converted by the signal conversion unit and calculates a phase difference between the first and second pulse signals as a calculated phase difference, and a torque calculation unit that calculates a torque applied to the rotating shaft from the calculated phase difference and a coefficient corresponding to the rotating shaft, the phase difference calculation unit is connected to a memory unit that pre-stores, for each rotation angle of the reference disk, a phase difference between the first pulse signal and the second pulse signal during one rotation at a constant speed when the rotating shaft is rotating without load, as a zero-point correction phase difference; the torque calculation unit is configured to correct and calculate a torque applied to the rotating shaft based on the zero-point correction phase difference for each rotation angle of the reference disk stored in the memory unit, the current rotation angle of the reference disk, and the calculated phase difference; and the pre-storage unit is provided with a torque sensor that stores the zero-point correction phase difference for the entire circumference for each predetermined rotation angle of the reference disk.

2. The screw fastening device according to claim 1 , wherein the sensor is an optical sensor.

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