JP7656800B2 - Torque sensor and screw tightening device equipped with same - Google Patents

Description

The present invention relates to a torque sensor that detects the torque applied to a rotating shaft and a screw tightening device equipped with the same.

As shown 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 disposed on the rotation input side of the rotating shaft and rotates integrally with the rotating shaft, a comparison disk that is disposed on the rotation output side of the rotating shaft and rotates integrally with the rotating shaft, and a sensor that detects the rotation of the reference disk and comparison disk and outputs a pulse signal related to the rotation.

The reference disk and 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 gives the conventional torque sensor the characteristic of being able to realize a relatively simple structure without mechanical contact.

Japanese Utility Model Application Publication No. 63-161339

However, in conventional torque sensors, even if the rotating shaft is rotating without load, if the magnetic pole spacing of the reference disk and the comparison disk is uneven, as shown in Figures 3(a) and (b), the pulse signals related to the reference disk and the comparison disk output from the sensor will not match, resulting in a phase difference. This causes a problem with conventional torque sensors, in that they will erroneously detect that torque is being applied to the rotating shaft even when the rotating shaft is rotating without load.

In addition, in conventional torque sensors, even if the magnetic pole spacing of the reference disk and comparison disk are uniform, when the reference disk and comparison disk are attached to the rotating shaft, the axial centers of the reference disk and comparison disk may not coincide and may be offset, as shown in Figure 4. If the axial centers of the reference disk and comparison disk are offset in this manner, a phase difference similar to that described above will occur 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 takes into account the phase difference during no-load rotation described above, which causes the problem of inaccurate torque detection.

The present invention has an object 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 the torque sensor 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 torque sensor that calculates a torque applied to the rotating shaft from the calculated phase difference and a coefficient corresponding to the rotating shaft. and a torque calculation unit which calculates 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 storage unit, the current rotation angle of the reference disk, and the calculated phase difference, wherein the phase difference calculation unit is connected to a memory unit which pre-stores the 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 for each rotation angle of the reference disk, and 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 storage unit, the current rotation angle of the reference disk, and the calculated phase difference, and the pre-storage unit stores the zero-point correction phase difference for the entire circumference for each predetermined rotation angle of the reference disk.
Also, it is preferable that the sensor is an optical sensor.

The torque sensor and screw tightening device equipped with the torque sensor according to the present invention correct the torque added to the rotation torque based on the zero-point correction phase difference in the memory 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 eliminates problems caused by improper installation of the reference disk and the comparison disk as in the conventional method, and has the advantage of ensuring high torque detection accuracy without having to precisely determine the installation position of the sensor in advance. In addition, since the torque sensor and 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, 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 manufacturing. Moreover, since the torque sensor and 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, 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.

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

The torque sensor according to the present invention and the 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 together with the rotating shaft 5, sensors S1 and S2 that detect the reference disk 10 and the comparison disk 20 and transmit signals, and a 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.

The rotating shaft 5 has a small diameter in its middle section 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 it is heat-treated to improve its toughness and strength. By setting the middle section to a small diameter, it is easily twisted when subjected to torque. The shaft 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 region within the torque detection range.

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 multiple notches 11 (21) arranged radially as shown in Figures 3 and 4. The notches 11 (21) are formed by cutting out a portion of the metal so that the light emitted from the sensors S1 and S2 can pass through.

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 or OFF signal to the outside indicative of whether or not the notches 11 and 12 have been detected.

The torque detection means 30 includes a signal conversion unit 50 that converts the ON and OFF signals output from the sensors S1 and S2 into a pulse signal, a phase difference calculation unit 60 that calculates the phase difference between the first pulse signal related to sensor S1 and the second pulse signal related to sensor S2 output from the signal conversion unit 50 as a calculated phase difference, a memory unit 70 that 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, in association with each other, and a torque calculation unit 80 that corrects and calculates the torque applied to the rotating shaft 5 based on the memory information stored in the memory unit 70 and the calculated phase difference.

The signal conversion unit 50 comprises 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.

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.

The memory unit 70 stores the calculated phase difference for each rotation angle of the reference disk 10 transmitted from the phase difference calculation unit 60 in a linked manner, and is configured to store this stored information in advance as a zero point correction value of the torque sensor 1. The memory unit 70 also stores a preset coefficient related to the elastic deformation of the rotating shaft 5. The zero point correction value corrects the error of the reference disk 10 and the comparison disk 20 when the rotating shaft 5 rotates without load, and can ensure the accuracy of the detected torque even when the intervals of the notches 11 (21) are uneven as shown in Figures 3(a), (b) and 4, or when the axial centers of the reference disk 10 and the comparison disk 20 are offset.

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. In addition, the rotation angle of the reference disk 10 is preset as an equal division of 360 degrees, specifically set in increments of 0.005 degrees.

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 with a zero point correction value 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 coefficient 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, making it possible to accurately measure the torque applied to the rotating shaft 5.

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

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 number of various parameters related to the rotation drive, such as the rotation speed of the output shaft Ma of the motor M and the tightening completion torque.

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 tightening 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 tightening completion torque.

The operation of the torque sensor 1 configured in this way 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 the output shaft Ma of the motor M, about 1 min^-1 to 5 min^-1, and is completed by collecting the zero point correction value that links the rotation angle of the reference disc 10 and the calculated phase difference calculated by the phase difference calculation unit 60 corresponding 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 memory unit 70.

This calibration makes it possible to clarify the calculated phase difference between the first and second pulse signals generated during no-load rotation, thereby making it possible to correct the zero point error caused by 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, the torque error for each rotation angle of the rotating shaft 5 can be appropriately corrected. Therefore, the screw tightening 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.

In this embodiment, the reference disk 10 and the comparison disk 20 are thin metal disks, but they 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 they may have different structures, such as the reference disk 10 being a thin disk and the comparison disk 20 being a cylinder. Furthermore, the sensors S1 and S2 may be optical sensors and magnetic sensors, respectively. 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 this 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 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 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 this 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.

REFERENCE SIGNS LIST 1 ... torque sensor 5 ... rotating shaft 10 ... reference disk 20 ... comparison disk 30 ... torque detection means 50 ... signal conversion section 60 ... phase difference generating section 80 ... torque calculation section 90 ... screw tightening device S1, S2 ... sensor

Claims (2)

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

Images