WO2009104676A1 - 送り駆動装置のバックラッシ量検知方法、及び送り駆動装置のバックラッシ量検知装置 - Google Patents
送り駆動装置のバックラッシ量検知方法、及び送り駆動装置のバックラッシ量検知装置 Download PDFInfo
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- WO2009104676A1 WO2009104676A1 PCT/JP2009/052890 JP2009052890W WO2009104676A1 WO 2009104676 A1 WO2009104676 A1 WO 2009104676A1 JP 2009052890 W JP2009052890 W JP 2009052890W WO 2009104676 A1 WO2009104676 A1 WO 2009104676A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
- B23Q5/00—Driving or feeding mechanisms; Control arrangements therefor
- B23Q5/54—Arrangements or details not restricted to group B23Q5/02 or group B23Q5/22 respectively, e.g. control handles
- B23Q5/56—Preventing backlash
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
- B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
- B23Q5/00—Driving or feeding mechanisms; Control arrangements therefor
- B23Q5/22—Feeding members carrying tools or work
- B23Q5/34—Feeding other members supporting tools or work, e.g. saddles, tool-slides, through mechanical transmission
- B23Q5/38—Feeding other members supporting tools or work, e.g. saddles, tool-slides, through mechanical transmission feeding continuously
- B23Q5/40—Feeding other members supporting tools or work, e.g. saddles, tool-slides, through mechanical transmission feeding continuously by feed shaft, e.g. lead screw
Definitions
- the present invention relates to a backlash amount detection method for a feed drive device and a backlash amount detection device for a feed drive device.
- the present invention relates to a technique for detecting a backlash amount by causing a driven body to perform a reciprocating motion whose amplitude or frequency changes, and analyzing data on the amplitude of position feedback and the amplitude of motor torque.
- the rotational motion of the servo motor is transmitted to the driven body through a motion transmission mechanism including a gear and a ball screw mechanism to perform a desired motion. If the motion transmission mechanism is used for a long period of time, the backlash due to wear or the like increases and the motion accuracy decreases. Continuing to use the numerically controlled machine tool in a state where the motion accuracy has deteriorated will produce a large amount of defective products and cause enormous losses.
- Patent Document 1 discloses a backlash prevention technology for a drive device that determines that there is degradation when vibrations generated in motor torque during exercise become equal to and greater than a threshold value.
- the frictional force measuring technology for machine tools disclosed in Patent Document 2 the frictional torque of the rotation system of the feed drive system and the frictional force of the linear movement system are simply measured using the NC control unit. When the measured frictional force is out of the preset allowable range, it is determined that there is deterioration.
- An object of the present invention is to provide a backlash amount detection method and a backlash amount detection device capable of detecting a backlash amount existing in a motion transmission system.
- a backlash amount detection method for a feed driving device includes a driven body, a ball screw mechanism for linearly moving and driving the driven body, and a ball screw shaft of the ball screw mechanism.
- the motion transmission system is calculated from the relationship between the amplitude of the position feedback and the amplitude of the motor torque.
- a second step of estimating the magnitude of the backlash to be stationary.
- the backlash existing in the motion transmission system can be estimated easily in a short time and with high accuracy without using a special measuring instrument.
- the backlash amount detection method of the feed drive device can also perform correlation data acquisition and backlash amount estimation calculation using a control unit that controls the servo motor.
- a backlash amount detection method for a feed driving device includes a driven body, a ball screw mechanism for linearly moving and driving the driven body, and a ball screw shaft of the ball screw mechanism.
- the driven body Via the ball screw mechanism, the driven body is caused to perform a reciprocating motion whose frequency changes, and first correlation data of position feedback amplitude and frequency and second correlation data of motor torque amplitude and frequency are obtained.
- the backlash existing in the motion transmission system can be estimated easily in a short time and with high accuracy without using a special measuring instrument.
- the driven body performs the reciprocating motion in which the frequency is constant and the amplitude gradually changes.
- the amplitude of the position feedback when the rate of change in the amplitude of the motor torque is equal to or greater than a predetermined value may be estimated as the backlash magnitude (backlash amount).
- the driven body performs the reciprocating motion in which the amplitude is constant and the frequency is gradually changed.
- a first frequency that is a frequency at which the amplitude of the motor torque is maximized among frequencies at which the amplitude of the motor torque is equal to or greater than the friction torque is obtained, and the first frequency and
- the amplitude of the position feedback at the second frequency that is the frequency at which the amplitude of the motor torque is the minimum among the same value or the frequency that is larger than the first frequency may be estimated as the magnitude of the backlash.
- the first frequency at which the amplitude of the motor torque is maximized is obtained from the frequencies at which the amplitude of the motor torque is equal to or greater than the friction torque. Thereafter, the position feedback amplitude at a frequency that minimizes the amplitude of the motor torque among the frequencies that are equal to or greater than the first frequency can be accurately detected. Therefore, the backlash amount can be detected with high accuracy.
- the backlash amount detection method for a feed drive device includes the reciprocating motion under a condition in which an inertial force larger than a frictional force existing in the motion transmission system is generated in the first step. May be performed by the driven body.
- a backlash amount detection device for a feed driving device includes a driven body, a ball screw mechanism for linearly moving and driving the driven body, and a ball screw shaft of the ball screw mechanism.
- a backlash amount detecting device for detecting the amount of backlash existing in a motion transmission system in a feed driving device having a servo motor for rotationally driving the servo motor and a control unit for driving and controlling the servo motor.
- a data acquisition unit for causing the driven body to perform reciprocating motion in which the amplitude is changed by driving the servo motor, thereby obtaining correlation data between the amplitude of the position feedback and the amplitude of the motor torque. And using the correlation data acquired by the data acquisition unit, the amplitude of the position feedback and the amplitude of the motor torque And a backlash quantity calculating section for estimating the magnitude of the backlash present in the motion transmission system from the relationship.
- the backlash existing in the motion transmission system can be estimated easily in a short time and with high accuracy without using a special measuring instrument. Therefore, the operator can diagnose the deterioration state of the drive mechanism during the regular periodic inspection without stopping the production line for the purpose of measuring the backlash amount. Operators can find and fix problems before a failure that affects the entire production line occurs.
- the backlash amount detection device of the feed drive device can also perform correlation data acquisition and backlash amount estimation calculation using a control unit that controls the servo motor.
- a backlash amount detection device for a feed driving device includes a driven body, a ball screw mechanism for linearly moving and driving the driven body, and a ball screw shaft of the ball screw mechanism.
- a backlash amount detecting device for detecting the amount of backlash existing in a motion transmission system in a feed driving device having a servo motor for rotationally driving the servo motor and a control unit for driving and controlling the servo motor.
- the driven body By driving and controlling the servo motor, the driven body is caused to perform a reciprocating motion whose frequency changes via the ball screw mechanism, and the first correlation data of the position feedback amplitude and frequency, the motor torque amplitude and A data acquisition unit for acquiring second correlation data of the frequency, and the first correlation data and the second correlation acquired by the data acquisition unit Using chromatography data and a backlash quantity calculating section for estimating the magnitude of the backlash present in the motion transmission system.
- the backlash existing in the motion transmission system can be estimated easily in a short time and with high accuracy without using a special measuring instrument.
- the data acquisition unit causes the control unit to drive and control the servo motor, so that the frequency is constant and the amplitude gradually changes.
- the reciprocating motion is performed on the driven body via the ball screw mechanism to acquire the correlation data
- the backlash amount calculation unit is configured to calculate the motor torque based on the correlation data acquired by the data acquisition unit.
- the amplitude of the position feedback when the rate of change in amplitude is equal to or greater than a predetermined value may be estimated as the magnitude of backlash.
- the backlash amount detection device of the feed drive device can accurately detect the backlash amount.
- the data acquisition unit causes the driven body to perform the reciprocating motion in which the amplitude is constant and the frequency is gradually changed.
- One correlation data and the second correlation data are acquired, and the backlash amount calculation unit is based on the second correlation data acquired by the data acquisition unit, and the amplitude of the motor torque is equal to or equal to the friction torque.
- a second frequency determining unit that obtains a second frequency that is the same frequency as the one frequency or greater than the first frequency, and is the frequency at which the amplitude of the motor torque is minimized. , From the first correlation data by the data acquisition unit has acquired, may estimate the amplitude of said position feedback when the second frequency, wherein the second frequency determining unit has determined as the magnitude of the backlash.
- the data acquisition unit is configured to perform the reciprocation under a condition in which an inertial force larger than a frictional force existing in the motion transmission system is generated. Data may be acquired by causing the driven body to exercise.
- FIG. 6 It is a diagram of the experimental result of the motor torque command at the time of step response. It is explanatory drawing of the dynamic model of the feed drive mechanism which considered the spring characteristic of the backlash.
- 6 is a time chart showing servo data (position command and position feedback) when the amplitude is changed at a frequency of 10 Hz. It is a time chart which shows the servo data (motor torque command) when changing an amplitude at a frequency of 10 Hz. 6 is a time chart showing servo data (position command and position feedback) when the amplitude is changed at a frequency of 50 Hz. It is a time chart which shows the servo data (motor torque command) when changing an amplitude with a frequency of 50 Hz.
- FIG. 24 is a chart showing a data example of a motor torque command and position feedback acquired by the data acquisition control of FIG. 23. It is a flowchart of the data acquisition control following the data acquisition control of FIG. 23, and a backlash amount estimation calculation process. It is a table
- surface which shows the experimental value and estimated value of the amount of backlash in the case of load mass 0kg. It is a graph which shows the estimated value of the load mass and backlash amount in the case of actual measurement backlash amount of 40 micrometers.
- the machining center 1 performs a desired machining (for example, “milling”, etc.) on the workpiece by independently moving the workpiece and the tool relative to each axis in the XYZ orthogonal coordinate system. It is a machine tool that can perform “drilling”, “cutting” and the like.
- the machining center 1 mainly includes a base 2, a machine body 3 (see FIG. 2), and a splash cover 4.
- the base 2 is a cast iron base.
- the machine main body 3 is located on the upper part of the base 2 and performs cutting of the workpiece.
- the splash cover 4 is box-shaped and covers the upper part of the machine body 3 and the base 2.
- the base 2 is a substantially rectangular parallelepiped casting that is long in the Y-axis direction. At the four corners at the bottom of the base 2, leg portions 2a capable of height adjustment are provided.
- the machining area of the machine body 3 (see FIG. 2) is provided inside the splash cover 4.
- An opening is provided on the front surface of the splash cover 4.
- a pair of sliding doors 5 and 6 are provided in the opening.
- the open / close doors 5 and 6 are respectively provided with rectangular glass window portions 5a and 6a.
- the opening / closing doors 5 and 6 are provided with handle portions 5b and 6b. Opening the handle portions 5b and 6b away from each other opens the opening portion, and the operator attaches / detaches the workpiece to / from the table 10 (see FIG. 2) as a driven body fixed on the base 2. .
- the operation panel 80 is provided on the right side of the opening.
- the operation panel 80 includes a keyboard 81 having a numeric keypad and various operation keys.
- the operation panel 80 includes a liquid crystal display 82 for displaying a setting screen or an execution operation above the keyboard 81. The operator can set a machining program for executing workpiece machining, various parameters, and the like by checking the display 82 of the operation panel 80 and operating the keyboard 81.
- the machine main body 3 mainly includes a column 16, a spindle head 7, a spindle (not shown), a tool changer (ATC) 20, and a table 10.
- the column 16 is fixed to the upper surface of the column seat 23 at the rear of the base 2 and extends vertically upward.
- the spindle head 7 can move up and down along the front surface of the column 16, and supports the spindle in a rotatable manner.
- the tool changer 20 is located on the right side of the spindle head 7 and exchanges a tool holder held at the tip of the spindle with another tool holder.
- the table 10 is located at the upper part of the base 2 and fixes the work detachably.
- a box-like control box 19 is provided on the rear side of the column 16.
- the control box 19 includes a numerical controller 50 that controls the operation of the machining center 1 therein.
- the table 10 uses an X-axis motor 71 (see FIG. 4) and a Y-axis motor 72 (see FIG. 4) that are servo motors, It moves in the Y-axis direction (the depth direction of the machine body 3).
- the moving mechanism has the following configuration.
- a rectangular parallelepiped support 12 is provided below the table 10.
- the support base 12 is provided with a pair of X-axis feed guide rails extending along the X-axis direction at the upper part thereof.
- the pair of X-axis feed guide rails supports the table 10 so as to be movable on the upper part thereof.
- the support base 12 is located at the upper part of the base 2.
- the base 2 is provided with a pair of Y-axis feed guide rails extending along the longitudinal direction at the upper part thereof.
- the pair of Y-axis feed guide rails support the support base 12 so as to be movable upward.
- the table 10 is moved in the X-axis direction along the X-axis feed guide rail by the X-axis motor 71 provided on the support base 12.
- the table 10 is a Y-axis motor 72 provided on the base 2 and moves in the Y-axis direction along the Y-axis feed guide rail.
- Telescopic covers 13 and 14 that contract in a telescopic manner cover the X-axis feed guide rail.
- the telescopic cover 15 and the Y-axis rear cover cover the Y-axis feed guide rail.
- the telescopic covers 13, 14, 15 and the Y-axis rear cover always cover the X-axis feed guide rail and the Y-axis feed guide rail.
- a guide rail extending in the vertical direction on the front side of the column 16 supports the spindle head 7 so as to be movable up and down via a linear guide.
- the spindle head 7 is connected to a feed screw provided on the front side of the column 16 so as to extend in the vertical direction with a nut.
- the spindle head 7 is driven up and down in the vertical direction by rotationally driving the feed screw in the forward and reverse directions by the Z-axis motor 73 (see FIG. 4).
- the servo amplifier 63 drives the Z-axis motor 73 based on a control signal from the CPU 51 of the numerical controller 50, so that the spindle head 7 is driven up and down.
- the tool changer 20 includes a tool magazine 21, a tool change arm 22, and the like.
- the tool magazine 21 stores a plurality of tool holders that support the tool 26.
- the tool change arm 22 grips and conveys the tool holder.
- the control device 50 as a control unit includes a microcomputer, and includes an input / output interface 54, a CPU 51, a ROM 52, a RAM 53, axis control circuits 61a to 64a and 75a, and servo amplifiers 61 to 64, current detectors 61b to 64b, and differentiators 71b to 74b.
- the servo amplifiers 61 to 64 are connected to an X-axis motor 71, a Y-axis motor 72, a Z-axis motor 73, and a main shaft motor 74, respectively.
- the axis control circuit 75 a is connected to the magazine motor 75.
- the X-axis motor 71 and the Y-axis motor 72 are for moving the table 10 in the X-axis direction and the Y-axis direction.
- the magazine motor 75 is for rotating the tool magazine 21.
- the main shaft motor 74 is for rotating the main shaft.
- the X-axis motor 71, the Y-axis motor 72, the Z-axis motor 73, and the main shaft motor 74 are provided with encoders 71a to 74a, respectively.
- the axis control circuits 61a to 64a receive a movement command amount from the CPU 51 and output a current command (motor torque command) to the servo amplifiers 61 to 64.
- the servo amplifiers 61 to 64 receive a current command and output a drive current to the motors 71 to 74.
- the axis control circuits 61a to 64a receive position feedback signals from the encoders 71a to 74a and control position feedback.
- the differentiators 71b to 74b differentiate the position feedback signals received from the encoders 71a to 74a, convert them into speed feedback signals, and output the speed feedback signals to the axis control circuits 61a to 64a.
- the axis control circuits 61a to 64a receive the speed feedback signal from the differentiators 71b to 74b and control the speed feedback.
- the current detectors 61b to 64b detect drive currents output from the servo amplifiers 61 to 64 to the motors 71 to 74.
- the current detectors 61b to 64b feed back the detected drive current to the axis control circuits 61a to 64a.
- the axis control circuits 61a to 64a control the current (torque) with the drive current fed back by the current detectors 61b to 64b.
- the drive current flowing through the motors 71 to 74 and the load torque applied to the motors 71 to 74 are approximately the same. Therefore, the load torque applied to the motors 71 to 74 can be detected by the current detectors 61b to 64b that detect the drive currents flowing through the motors 71 to 74.
- the axis control circuits 61a to 64a receive the movement command amount from the CPU 51 and drive the magazine motor 75.
- a display 82 as a notification mechanism and an operation input unit 81 provided with operation keys and the like.
- Example 1 in the case where the present invention is applied to the machining center 1 will be described in detail.
- the X-axis feed drive mechanism converts the rotational motion of the servo motor 71 (X-axis motor) into a straight motion through a ball screw shaft 76 and a nut 77 constituting the ball screw mechanism, 10 is driven.
- the bearing 78 restrains the movement of the ball screw shaft 76 in the axial direction.
- a system that converts the rotational motion of the servo motor 71 described above into a straight motion and drives the table 10 is referred to as a motion transmission system.
- the X-axis feed drive mechanism indicates a servo motor (X-axis motor 71), a bearing 78, a ball screw shaft 76, a nut 77, and the table 10.
- the X-axis feed drive device indicates a device in which a control device 50 is connected to an X-axis feed drive mechanism.
- the machining center 1 can perform three-dimensional cutting by combining three sets of feed drive mechanisms in the X, Y, and Z axis directions having the same structure.
- feed accuracy the accuracy of the feed movement of the feed drive mechanism
- backlash exists between the bearing 78 and the ball screw shaft 76 and between the ball screw shaft 76 and the nut 77 due to wear or the like, the feed drive mechanism can restrain the axial movement of the table 10. Therefore, the feed accuracy decreases.
- the inventor examined the influence of the backlash existing in the motion transmission system in the feed driving device on the feed accuracy of the machining center 1.
- 6 and 7 show the results when the feed drive mechanism is operated based on the shape defined by JIS (Japanese Industrial Standards) B6336-7.
- FIG. 6 shows a normal state without backlash.
- FIG. 7 shows a case where backlash exists in the feed driving device in the X-axis direction. As can be seen from these figures, the feed accuracy is greatly reduced when the backlash exists.
- the inventor conducted a step response simulation and an experiment to examine whether the backlash amount can be estimated.
- the simulation is disclosed in the paper “Kakino et al., Research on Total Tuning of Feed Drive System in NC Machine Tools (1st Report), Journal of Precision Engineering, Vol.60, No.8 (1994) pp.1097-1101.” It was done with reference to the model.
- the feed driving device used in the experiment has a backlash amount of about 10 ⁇ m between the bearing 78 and the ball screw shaft 76 and about 20 ⁇ m between the ball screw shaft 76 and the nut 77. The same amount of backlash was assumed in the simulation. 8 and 9 show the simulation results and experimental results of the step response.
- the position command is given in steps of 10 ⁇ m from 0 ⁇ m to 50 ⁇ m.
- the solid line indicates the position command
- the broken line indicates the position of the table 10.
- the table 10 hardly moves while the position command is smaller than the backlash amount of 30 ⁇ m or 30 ⁇ m which is the same as the backlash amount.
- the position command exceeds 30 ⁇ m, the table 10 moves.
- the table 10 actually moves little by little even when the position command is smaller than the backlash amount.
- FIGS. 10 and 11 show the simulation results and the experimental results of the motor torque command when the movements of FIGS. 8 and 9 are performed, respectively.
- the motor torque command is more than doubled.
- the motor torque command gradually increases as the position command increases, and there is no clear relationship with the backlash amount.
- the difference between the experimental result and the simulation result is considered to be because there is a spring characteristic depending on the displacement in the region where the position command is smaller than the backlash amount. That is, even if backlash exists, the mechanical contact is never lost in practice. Therefore, the presence of steel balls, grease, or the like between the bearing 78 and the ball screw shaft 76 and between the ball screw shaft 76 and the nut 77 means that the feed drive mechanism has a spring characteristic.
- the friction characteristic of the linear guide guiding the linear motion of the table 10 shows a nonlinear spring characteristic depending on the displacement in a displacement region of several hundred ⁇ m or less (for example, Sato et al .: Friction in linear motion rolling guide) Experimental behavior analysis of characteristics, Transactions of the Japan Society of Mechanical Engineers (C ⁇ ), Vol.73, No.734, (2007), pp.2811-2819.).
- FIG. 12 is a mechanical model of the feed drive mechanism considering the above characteristics. Between the bearing 78 where the backlash exists and the ball screw shaft 76, and between the ball screw shaft 76 and the nut 77, there is a non-linear spring characteristic depending on the displacement in a region smaller than the backlash amount.
- the friction characteristic of the linear guide that guides the table 10 also has a spring characteristic that depends on the displacement in the minute displacement region, and the frictional force is saturated at a certain displacement or more.
- Equation (1) is the sum of the axial spring restoring force between the bearing 78 and the ball screw shaft 76 and between the ball screw shaft 76 and the nut 77, and the force due to the non-linear friction characteristic generated in the linear guide. Shows the balance.
- Equation (1) holds, the table moves even with a command smaller than the backlash amount.
- Kb (Xs) .Xs + Ka (Xn) .Xn ft (Xt) (1)
- Xn Xt ⁇ (L / 2 ⁇ ) ⁇ s ⁇ Xs (2)
- Kb (Xs) is a non-linear function with the axial displacement Xs of the ball screw shaft 76 as a variable, and indicates the axial spring stiffness between the bearing 78 and the ball screw shaft 76.
- Ka (Xn) is a non-linear function with the displacement Xn of the nut 77 relative to the ball screw shaft 76 as a variable, and indicates the axial spring stiffness of the ball screw shaft 76 and the nut 77.
- ft (Xt) is a non-linear function with the table displacement Xt as a variable, and indicates the frictional force of the linear guide.
- Kb axial spring stiffness between the bearing 78 and the ball screw shaft 76 [N / m]
- Xs axial displacement of the ball screw shaft 76 [m]
- Ka axial spring stiffness between the ball screw shaft 76 and the nut 77 [N / m]
- Xn displacement of the nut 77 relative to the ball screw shaft 76 [m]
- L Lead of ball screw shaft 76 [m] ⁇ s: rotation angle of the ball screw shaft 76 [rad]
- ft frictional force of linear guide [N]
- Xt Table displacement [m]
- Bb Backlash amount of bearing 78 [m]
- Bn Backlash amount [m] between the ball screw shaft 76 and the nut 77
- the movement of the table 10 at a very low speed in the minute displacement region is affected by the spring characteristics existing in the backlash and the non-linear friction characteristics existing in the linear guide. Therefore, it is difficult to estimate the backlash amount from the motor torque command.
- the motor torque command increases when the position command exceeds the backlash amount. Therefore, it is estimated that the backlash amount can be estimated from the displacement when the motor torque command changes.
- the inertial force of the table 10 is used as a method for estimating the backlash amount.
- the table 10 is driven under the condition that an inertial force larger than the spring characteristic force existing inside the backlash is generated, the table 10 does not move in a region where the displacement is smaller than the backlash amount (a minute displacement region). In a region where the displacement is larger than the backlash amount, the table 10 also moves. Therefore, it is considered that the backlash amount can be estimated from the change in the motor torque command when the table 10 moves.
- Acceleration is required to generate inertial force. In order to give acceleration, it is effective to perform a sinusoidal reciprocating motion. When a sinusoidal reciprocating motion is performed, the acceleration is maximized when the displacement is maximized.
- FIG. 13 and FIG. 14 show the result of performing a motion in which the frequency of the position command is fixed at 10 Hz and the amplitude of the position command changes stepwise from 20 to 520 ⁇ m in steps of 20 ⁇ m in the feed drive mechanism in which a backlash of about 20 ⁇ m exists.
- FIG. 13 shows the measurement results of the position command and position feedback.
- FIG. 14 shows the measurement result of the motor torque command. For each amplitude, a sine wave reciprocation of 5 reciprocations, that is, 0.5 seconds is performed.
- the position feedback is obtained by converting the rotation angle output from the rotary encoder 71a provided at the motor end into a table displacement.
- the amplitude of the position feedback is smaller than the amplitude of the position command. This cause is a response delay of the control system, which is a general phenomenon. As shown in FIG. 14, the amplitude of the motor torque command is substantially constant regardless of the change in the position feedback amplitude (change in inertial force).
- the motor torque command during movement is affected by both frictional force and inertial force acting on the feed drive mechanism.
- the value of the motor torque command during constant speed motion was 0.5 to 1.0 Nm.
- the value of the amplitude of the motor torque command is approximately 1.0 Nm. Therefore, in the 10 Hz reciprocating motion, it is estimated that the influence of the frictional force is more dominant than the inertial force, and the influence of the backlash is less likely to appear.
- 15 and 16 show the results when the same measurement experiment as in FIGS. 13 and 14 was performed at a frequency of 50 Hz.
- the reciprocating motion at each amplitude is performed for 0.5 seconds.
- the amplitude of the position feedback is smaller than when the frequency is 10 Hz (see FIG. 13). This is due to the response delay of the control system.
- the result is significantly different from the result when the frequency is 10 Hz (see FIG. 14), and the amplitude of the motor torque command increases rapidly in the vicinity of 2 seconds. Thereafter, the amplitude of the motor torque command increases linearly.
- the inertial force F when the reciprocating motion with the amplitude A and the angular frequency ⁇ is performed on the table 10 of the mass M is expressed by Equation (3).
- the inertial force F is proportional to the square of the angular frequency ⁇ . If the reciprocating motion is performed under the condition that the inertial force F represented by the expression (3) is sufficiently larger than the frictional force and the spring characteristic force of the backlash, the influence of the backlash appears in the motor torque command.
- F -MA ⁇ 2 sin ⁇ t (3)
- FIG. 17 shows the correlation between the amplitude of the position feedback and the amplitude of the motor torque command in the above-described experiment. As shown in FIG. 17, when there is no backlash, the amplitude of the position feedback is proportional to the amplitude of the motor torque command. When backlash exists, the amplitude of the motor torque command increases rapidly when the position feedback amplitude corresponding to the backlash amount and the position feedback amplitude larger than the backlash amount are reached.
- FIG. 18 shows the experimental results when the above-described experiment was performed while changing the load mass placed on the table 10. The experiment was performed in the presence of a backlash of about 40 ⁇ m. As shown in FIG. 18, when the load mass arranged on the table 10 increases, the amplitude of the motor torque command increases in a region where the amplitude of the position feedback is larger than the backlash amount. On the contrary, the displacement at which the amplitude of the motor torque command changes does not change even when the load mass arranged on the table 10 increases.
- the backlash magnitude (backlash amount) existing in the feed drive mechanism can be estimated based on the amplitude of the position feedback when the amplitude of the motor torque command changes greatly.
- the amplitude of the motor torque command does not change stepwise with the backlash amount as a boundary, but gradually changes as the amplitude of the position feedback increases.
- the cause is considered to be that the spring characteristics in the presence of backlash change smoothly as a function of displacement.
- the backlash amount is estimated using the second-order derivative of the amplitude of the motor torque command.
- 19 and 20 show the results of calculating the derivative (time derivative) of the motor torque command from the result of FIG.
- FIG. 19 shows the results for the X-axis feed drive mechanism.
- FIG. 20 shows the results for the Y-axis feed drive mechanism.
- an X-axis feed drive mechanism is disposed on the Y-axis feed drive mechanism. Therefore, the mass of the driven body on the Y axis is considerably larger than the mass of the driven body on the X axis. There is no backlash in the Y-axis feed drive mechanism.
- the differential of the amplitude of the motor torque command is large when the amplitude of the position feedback corresponds to the backlash amount.
- the amplitude of the motor torque command changes rapidly when the amplitude of the position feedback corresponding to the backlash amount. Therefore, the amplitude of the position feedback when the differential of the amplitude of the motor torque command is maximized can be used as the estimated value of the backlash amount.
- the backlash amount is estimated simply by looking at the maximum differential value, the backlash amount is estimated even when there is actually no backlash. For example, looking at the result when there is no backlash shown in FIG. 19, the differentiation is maximized when the position feedback amplitude is about 120 ⁇ m. In this case, although the backlash does not exist, it is erroneously estimated that the backlash amount is 120 ⁇ m.
- ⁇ Set a threshold to prevent incorrect estimation. If the maximum differential value of the amplitude of the motor torque command is equal to or less than the threshold value, it is determined that no backlash exists. In the case of the result of FIG. 19, if the threshold is set to 1, the backlash amount can be estimated only when the backlash actually exists. However, looking at the results for the Y-axis feed drive mechanism shown in FIG. 20, the differential of the amplitude of the motor torque command exceeds the threshold value even though there is no backlash on the Y-axis. This is because the Y-axis load mass is large and the inertial force is large.
- FIG. 21 shows the relationship between the position feedback amplitude and the second derivative of the motor torque command amplitude for the X-axis feed drive mechanism.
- FIG. 22 shows the relationship between the amplitude of the position feedback and the second derivative of the amplitude of the motor torque command for the Y-axis feed drive mechanism.
- the second-order derivative of the amplitude of the motor torque command is within the set threshold even in the Y-axis feed drive mechanism having a large mass. Therefore, if the second derivative of the amplitude of the motor torque command is used, the backlash amount can be estimated without changing the threshold value.
- the control program for data acquisition control in FIG. 23 and backlash amount estimation calculation processing in FIG. 25 is stored in the ROM 52 in advance.
- the control device 50 controls the X-axis and Y-axis motors 71 and 72 via the axis control circuits 61 a and 62 a and the servo amplifiers 61 and 62.
- the control device 50 executes a sine wave reciprocating motion in which the amplitude is changed at a fixed frequency in the X-axis and Y-axis feed drive mechanisms.
- the flowchart shown in FIG. 23 is executed when a predetermined start command is input from the operation input unit 81 to the control device 50.
- the CPU 51 sets the amplitude X of the position command to 20 ⁇ m (initial value) (S1).
- the CPU 51 executes a reciprocating motion with a frequency of 50 Hz and a position command amplitude of X ⁇ m in the X-axis and Y-axis feed drive mechanisms (S2).
- the CPU 51 acquires the value of the motor torque command and the value of the position feedback at a cycle of 1 msec and stores them in the RAM 53 (S3).
- the values of the motor torque command and position feedback can be acquired from data input and output by the axis control circuits 61a and 62a.
- FIG. 24 shows an example of values acquired in S3.
- CPU51 determines whether 0.5 second has passed (S4). If it has not elapsed (S4: No), the process returns to S2. If it has elapsed (S4: Yes), the CPU 51 determines whether or not the amplitude of the position command is 520 ⁇ m or larger than 520 ⁇ m (S5). When smaller than 520 ⁇ m (S5: No), the CPU 51 increments the amplitude X of the position command by 20 ⁇ m (S6), and proceeds to S2. If the amplitude of the position command is greater than 520 ⁇ m or 520 ⁇ m (S5: Yes), the necessary data has been acquired, and the process is terminated.
- the CPU 51 executes the backlash amount estimation calculation process shown in FIG. 25 when a predetermined start command is input from the operation input unit 81.
- the CPU 51 calculates correlation data indicating a correlation between the amplitude of the position feedback and the amplitude of the motor torque command from the value acquired by the data acquisition control (see FIG. 23).
- the CPU 51 stores the calculated results in the RAM 53 in chronological order (S10).
- FIG. 17 is a diagram showing the calculated correlation data.
- the control device 50 that executes the control of FIG. 23 and the control of S10 corresponds to a data acquisition unit.
- the CPU 51 processes correlation data between the amplitude of the position feedback and the amplitude of the motor torque command, and calculates the second-order derivative of the amplitude of the motor torque command (S11).
- 21 and 22 are graphs showing the second derivative of the amplitude of the motor torque command.
- the differentiation is to obtain a difference value between adjacent values for the calculation result stored in time series in S10.
- the second order differentiation is to obtain a difference between values obtained by differentiation.
- the CPU 51 determines whether the maximum value of the second derivative of the amplitude of the motor torque command is greater than a predetermined threshold value or a threshold value (S12).
- the predetermined threshold is, for example, 1.0 Nm. If the CPU 51 determines that it is less than the threshold (S12: No), it determines that the machine is normal (no harmful backlash exists) (S13) and ends the process.
- the CPU 51 determines that the maximum value of the second derivative is greater than a predetermined threshold value or greater than the threshold value (S12: Yes)
- the data number N that maximizes the second derivative of the amplitude of the motor torque command is stored in the RAM 53. (S14).
- the CPU 51 estimates the amplitude of the position feedback of the data number N as the backlash amount B (S15).
- the CPU 51 displays a message indicating that the Bmm backlash amount has been detected on the display 82, and stores in the RAM 53 that the Bmm backlash amount has been detected (S16). After S16, this control ends.
- the control device 50 that executes the control of S11 to S16 in FIG. 25 corresponds to the backlash amount calculation unit.
- the time when the second-order differentiation is maximized is the time when the amplitude of the motor torque command changes abruptly. If there is no problem even if the accuracy is low, differentiation may be used without using second order differentiation. In that case, the time when the difference in the amplitude of the motor torque command stored in the RAM 53 is maximized is determined as a sudden change.
- FIG. 26 shows the results of experiments on feed drive mechanisms with different backlash amounts. As shown in FIG. 26, it was possible to estimate the backlash amount by setting the error between the actually measured values within 10 ⁇ m.
- FIG. 27 shows experimental results when the load mass placed on the table 10 is changed in four ways in the feed drive mechanism having a backlash of about 40 ⁇ m. According to FIG. 27, the difference in load mass affects the estimation result of the backlash amount.
- the control device 50 causes the table 10 to perform a sine wave reciprocating motion in which the frequency is constant and the amplitude gradually increases, and the backlash amount is determined from the relationship between the position feedback amplitude and the motor torque command amplitude.
- the amplitude of the position command for the reciprocating motion is changed stepwise from 20 ⁇ m to 520 ⁇ m.
- the amplitude of the position command for the reciprocating motion may be continuously changed.
- the amplitude of the reciprocating position command may be reduced instead of increasing the amplitude.
- a reciprocating position command may change both amplitude and frequency.
- the control device 50 drives and controls the servo motors 71 and 72, and acquires servo data of motor torque commands and position feedback.
- the control device 50 acquires correlation data between the amplitude of the position feedback and the amplitude of the motor torque command from the acquired data.
- the control device 50 estimates the backlash amount by analyzing the acquired correlation data. Therefore, the worker can easily estimate the backlash existing in the motion transmission system in a short time and with high accuracy without using a special measuring instrument.
- the control device 50 calculates the second derivative of the amplitude of the motor torque command, and estimates the position feedback amplitude that maximizes the second derivative as the backlash amount. Therefore, the control device 50 can determine the presence of the backlash amount using a threshold value that is not related to the magnitude of the load mass.
- control device 50 Since the control device 50 performs the reciprocating motion in which the amplitude gradually changes, it is possible to accurately detect the amplitude of the position feedback when the rate of change of the motor torque command is large.
- a method of causing the table 10 to perform a reciprocating motion in which the frequency of the position command is gradually changed and the frequency is gradually changed is adopted. Even if a constant amplitude is commanded, the amplitude of the position feedback actually varies depending on the frequency due to the influence of the characteristics of the control system. Therefore, the same effect as when the amplitude is gradually changed can be obtained. Since the amplitude of the position feedback becomes small when the frequency is high, as a result, a corresponding acceleration can be generated even with a small amplitude motion. Therefore, it is considered that a small amount of backlash can be detected.
- FIG. 28 and 29 show the results when the position command amplitude is 0.1 mm and the reciprocating motion is performed while the frequency is changed stepwise from 10 Hz to 260 Hz.
- FIG. 28 shows the measurement result of position feedback (displacement).
- FIG. 29 shows the measurement results of the motor torque command. 28 and 29, it can be seen that the amplitudes of the position feedback and the motor torque command change stepwise as the frequency changes.
- FIG. 30 shows the result of plotting the amplitude of the position feedback with the horizontal axis as the frequency.
- FIG. 31 shows the result of plotting the amplitude of the motor torque command with the horizontal axis as the frequency.
- FIG. 30 indicates that the position feedback amplitude decreases as the frequency increases.
- the amplitude of the motor torque command increases up to a certain frequency.
- the amplitude of the motor torque command starts to decrease after taking the maximum value, and then increases again. It can be seen that the frequency at which the amplitude of the motor torque command is maximized and the frequency at which the amplitude is minimized vary depending on the magnitude of the backlash existing in the mechanism.
- the table 10 moves together in a low frequency range where the amplitude is large.
- the inertial force increases and the motor torque command increases.
- the position feedback amplitude becomes smaller than the backlash amount, and the rotational motion of the motor is not transmitted to the table. Therefore, the amplitude of the motor torque command is reduced.
- the amplitude of the position feedback is further reduced, but the amplitude of the motor torque command is increased due to the influence of the moment of inertia of the motor and the ball screw shaft.
- FIG. 32 shows the measurement result of the amplitude of the position feedback in an experiment in which a load mass was applied to the table 10 in the presence of a backlash of about 25 ⁇ m.
- FIG. 33 shows a measurement result of the amplitude of the motor torque command in the above-described experiment. According to FIGS. 32 and 33, in the region where the frequency is higher than 80 Hz where the amplitude of the motor torque command is minimal, the amplitude of the motor torque command does not change even when the load mass changes.
- the amplitude of the motor torque command increases as the load mass is increased, so that it can be seen that the table 10 is reciprocating. That is, it can be seen from FIG. 33 that the frequency at which the amplitude of the motor torque command is minimized is 80 Hz. From FIG. 32, the amplitude of the position feedback when the frequency is 80 Hz can be determined as 25 ⁇ m. The position feedback amplitude of 25 ⁇ m can be estimated as the backlash amount.
- FIG. 34 is a flowchart of the data acquisition control process.
- FIG. 35 is a flowchart of the backlash amount estimation calculation process.
- the data acquisition control shown in FIG. 34 is executed by the CPU 51 when a predetermined start command is input from the operation input unit 81.
- the CPU 51 sets the frequency Y to 10 Hz (initial value) (S20).
- the CPU 51 executes the reciprocating motion with the frequency YHz and the position command amplitude of 0.1 mm for the X-axis feed drive mechanism (S21).
- CPU51 acquires the value of a motor torque command and a position feedback with a 1 msec period, and stores it in RAM53 (S22).
- the values of the motor torque command and the position feedback are acquired from data input / output by the axis control circuit 61a.
- CPU51 determines whether 0.5 second has passed (S23). If 0.5 seconds have not elapsed (S23: No), the process returns to S21. When 0.5 second has elapsed (S23: Yes), the CPU 51 determines whether or not the frequency YHz is 260 Hz or higher than 260 Hz (S24). When the frequency is less than 260 Hz (S24: No), the CPU 51 increments the frequency Y by 10 Hz (S25), and proceeds to S21. When the frequency YHz is greater than 260 Hz or 260 Hz (S24: Yes), the CPU 51 ends the process because necessary data has been acquired.
- the backlash amount estimation calculation process is executed by the CPU 51 when a predetermined start command is input from the operation input unit 81.
- the CPU 51 uses the servo data acquired in the data acquisition control (see FIG. 34), the CPU 51 calculates the amplitude of the position feedback (see FIG. 32) and the amplitude of the motor torque command (see FIG. 33).
- the CPU 51 stores the calculated results in the RAM 53 in chronological order (S30).
- the CPU 51 searches for the frequency f1 at which the amplitude of the motor torque command is first maximized (S31).
- the CPU 51 determines whether or not the amplitude of the motor torque command at the frequency f1 is smaller than twice the motor torque command during the constant speed motion (S32). When the amplitude of the motor torque command is smaller than twice the motor torque command during the constant speed motion (S32: Yes), the CPU 51 searches for the frequency f1 at which the amplitude of the motor torque command is the next maximum (S33). The process proceeds to S34. When the amplitude of the motor torque command is not smaller than twice the motor torque command at the constant speed motion (S32: No), the CPU 51 proceeds to S34 as it is. The CPU 51 searches for a frequency f2 at which the frequency is greater than f1 or f1, and the amplitude of the motor torque command is minimized (S34). The CPU 51 estimates the position feedback amplitude at the frequency f2 as the backlash amount B (S35).
- the CPU 51 displays a message indicating that the backlash amount of Bmm has been detected on the display 82, and stores in the RAM 53 that the backlash amount of Bmm has been detected (S36). After S36, this control ends.
- the control device 50 that executes the control of FIG. 34 and the control of S30 corresponds to a data acquisition unit.
- the control device 50 that executes the control of S31 to S36 in FIG. 35 corresponds to the backlash amount calculation unit.
- CPU51 changed the frequency in steps from 10Hz to 260Hz, you may change it continuously. The frequency may be reduced instead of increasing. Amplitude and frequency may vary both.
- FIG. 36 shows the result of applying the method of estimating the backlash amount by changing the frequency to the feed drive mechanism in various states. As shown in FIG. 36, it was possible to estimate the backlash amount by setting the error between the actually measured values within 10 ⁇ m. The method of changing the frequency is more practical because it is not necessary to pay attention to the setting of the threshold.
- the control device 50 causes the table 10 to perform a sine wave reciprocating motion in which the amplitude is constant and the frequency gradually increases.
- the controller 50 acquires motor torque command and position feedback data.
- the control device 50 calculates correlation data between the amplitude and frequency of the position feedback and correlation data between the amplitude and frequency of the motor torque command from the acquired data.
- the control device 50 estimates the amplitude of the position feedback when the motor torque command has a minimum amplitude as the backlash amount. Therefore, the backlash amount detection method and the backlash amount detection device of the feed drive device can easily and quantitatively evaluate the size of the backlash existing in the feed drive mechanism.
- the backlash amount detection method and the backlash amount detection device of the feed drive device can easily estimate the backlash existing in the motion transmission system in a short time and with high accuracy without using a special measuring instrument.
- a sine wave is used as the reciprocating motion, but a cosine wave may be used.
- the amplitude of the motor torque command is used as the amplitude of the motor torque, but a drive current value may be used.
- the present invention can be applied to all mechanical devices having a structure for transmitting the rotational motion of a servo motor to a driven body via a motion transmission mechanism.
- the present invention can be applied to machine tools, various conveying devices, various manufacturing devices, various robots, electric power steering, aircraft auxiliary wing drive mechanisms, nuclear plant fuel rod lifting devices, sewing devices, and the like.
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Abstract
Description
特許文献2が開示している工作機械の摩擦力測定技術では、送り駆動系の回転系の摩擦トルク、及び直線移動系の摩擦力を、NC制御部を利用して簡単に測定する。測定した摩擦力が予め設定した許容範囲を外れた場合に、劣化があると判断する。
図1、図2に示すように、マシニングセンタ1は、ワークと工具とをXYZ直交座標系における各軸方向へ独立に相対移動させることで、ワークに所望の機械加工(例えば、「フライス削り」、「穴空け」、「切削」等)を施すことができる工作機械である。マシニングセンタ1は、ベース2と、機械本体3(図2参照)と、スプラッシュカバー4とを主に備えている。ベース2は、鋳鉄製の基台である。機械本体3はベース2の上部に位置し、ワークの切削加工を行う。スプラッシュカバー4は箱状であり、機械本体3とベース2の上部を覆う。
図2に示すように、機械本体3は、コラム16と、主軸ヘッド7と、主軸(図示外)と、工具交換装置(ATC)20と、テーブル10とを主に備えている。コラム16は、ベース2の後部のコラム座部23の上面に固定し、鉛直上方に延びる。主軸ヘッド7は、コラム16の前面に沿って昇降可能であり、内部に主軸を回転可能に支持している。工具交換装置20は、主軸ヘッド7の右側に位置し、主軸の先端に保持してある工具ホルダと他の工具ホルダとを交換する。テーブル10は、ベース2の上部に位置し、ワークを着脱可能に固定する。箱状の制御ボックス19は、コラム16の後部側に設けている。制御ボックス19は、その内部に、マシニングセンタ1の動作を制御する数値制御装置50を備えている。
図2に示すように、テーブル10は、サーボモータからなるX軸モータ71(図4参照)及びY軸モータ72(図4参照)を用いて、X軸方向(機械本体3の左右方向)及びY軸方向(機械本体3の奥行き方向)に移動する。移動機構は以下の構成からなる。直方体状の支持台12は、テーブル10の下側に設けている。支持台12は、その上部に、X軸方向に沿って延びる1対のX軸送りガイドレールを設けている。1対のX軸送りガイドレールは、その上部に、テーブル10を移動可能に支持している。
図2,図3に示すように、コラム16の前面側で上下方向に延びるガイドレールが、リニアガイドを介して主軸ヘッド7を昇降自在に支持している。主軸ヘッド7は、コラム16の前面側に上下方向に延びるように設けた送りネジに対してナットで連結している。送りネジをZ軸モータ73(図4参照)で正逆方向に回転駆動することで、主軸ヘッド7が上下方向に昇降駆動する。サーボアンプ63が、数値制御装置50のCPU51からの制御信号に基づいてZ軸モータ73を駆動することで、主軸ヘッド7が昇降駆動する。
図4に示すように、制御部としての制御装置50は、マイクロコンピュータを含み、入出力インタフェース54と、CPU51と、ROM52と、RAM53と、軸制御回路61a~64a,75aと、サーボアンプ61~64と、電流検出器61b~64bと、微分器71b~74bとを備えている。サーボアンプ61~64は、夫々X軸モータ71、Y軸モータ72、Z軸モータ73、主軸モータ74に接続している。軸制御回路75aはマガジンモータ75に接続している。
Kb(Xs)・Xs+Ka(Xn)・Xn=ft(Xt) (1)
Xn = Xt-(L/2π)θs-Xs (2)
Ka(Xn)は、ボールねじシャフト76を基準としたナット77の変位Xnを変数とした非線形の関数であり、ボールねじシャフト76及びナット77の軸方向ばね剛性を示す。
ft(Xt)は、テーブル変位Xtを変数とした非線形の関数であり、リニアガイドの摩擦力を示す。
Xs:ボールねじシャフト76の軸方向変位[m]
Ka:ボールねじシャフト76とナット77との間の軸方向ばね剛性[N/m]
Xn:ボールねじシャフト76を基準としたナット77の変位[m]
L:ボールねじシャフト76のリード[m]
θs:ボールねじシャフト76の回転角度[rad]
ft:リニアガイドの摩擦力[N]
Xt:テーブル変位[m]
Bb:ベアリング78のバックラッシ量[m]
Bn:ボールねじシャフト76とナット77との間のバックラッシ量[m]
R:R=L/2π
例えば、テーブル10が動かないように固定してX軸モータ71を駆動した場合、位置指令がバックラッシ量を超えたところでモータトルク指令が大きくなる。それ故、モータトルク指令が変化したときの変位からバックラッシ量を推定できると推測する。しかし、上記の方法を実施することは、現実的には難しい。
図14に示すように、モータトルク指令の振幅は、位置フィードバックの振幅の変化(慣性力の変化)に関係なくほぼ一定である。
F=-MAω2sinωt (3)
CPU51は、モータトルク指令の値、及び位置フィードバックの値を、1msec周期で取得し、RAM53に格納する(S3)。モータトルク指令、位置フィードバックの値は、軸制御回路61a,62aが入出力するデータから取得することができる。図24は、S3において取得した値の例を示す。
図25に示すバックラッシ量推定演算処理は、操作入力部81から所定の開始指令を入力すると、CPU51が実行する。CPU51は、データ取得制御(図23参照)で取得した値から、位置フィードバックの振幅とモータトルク指令の振幅との相関関係を示す相関データを算出する。CPU51は、算出した結果を時系列に沿ってRAM53に格納する(S10)。図17は、算出した相関データを示す図である。図23の制御、及びS10の制御を実行する制御装置50がデータ取得部に相当する。
CPU51は、モータトルク指令の振幅の2階微分の最大値が所定の閾値又は閾値より大きいか判定する(S12)。所定の閾値は、例えば1.0Nmである。CPU51は、閾値未満と判定した場合には(S12:No)、機械は正常(有害なバックラッシが存在しない)と判断し(S13)、処理を終了する。
本実施例においては、2階微分が最大となるときを、モータトルク指令の振幅が急激に変化したときとしている。精度が低くても問題がない場合は、2階微分を用いずに微分を用いてもよい。その場合、RAM53に格納したモータトルク指令の振幅の差分が最大となるときを、急激に変化したときと判断する。
周波数が高いときに位置フィードバックの振幅が小さくなるので、結果的に、小さい振幅の運動でも相応の加速度を発生させることができる。それ故、小さいバックラッシ量の検出が可能になると考える。
CPU51は、モータトルク指令、及び位置フィードバックの値を、1msec周期で取得し、RAM53に格納する(S22)。モータトルク指令、及び位置フィードバックの値は、軸制御回路61aが入出力するデータから取得する。
バックラッシ量推定演算処理は、操作入力部81から所定の開始指令を入力すると、CPU51が実行する。データ取得制御(図34参照)で取得したサーボデータを用いて、CPU51は、位置フィードバックの振幅(図32参照)、及びモータトルク指令の振幅(図33参照)を算出する。CPU51は、算出した結果を時系列に沿ってRAM53に記憶する(S30)。CPU51は、モータトルク指令の振幅が最初に極大になる周波数f1をサーチする(S31)。
上記実施例2では、CPU51は、周波数を10Hzから260Hzまで段階的に変化させたが、連続的に変化させてもよい。周波数は、大きくしていくのではなく、小さくしていってもよい。振幅及び周波数は、両方を変化させてもよい。
図36に示すように、実測値との間の誤差を10μm以内としてバックラッシ量を推定することができた。周波数を変化させる方法では、閾値の設定等に注意を払う必要はないので、より実用的である。
本実施例では、モータトルクの振幅として、モータトルク指令の振幅を用いているが、駆動電流値を用いてもよい。
Claims (10)
- 被駆動体と、前記被駆動体を直線的に移動駆動させる為のボールねじ機構と、前記ボールねじ機構のボールねじシャフトを回転駆動するサーボモータと、前記サーボモータを駆動制御する制御部とを有する送り駆動装置における運動伝達系に存在するバックラッシの大きさを検知するバックラッシ量検知方法であって、
前記サーボモータによって、前記ボールねじ機構を介して、振幅が変化する往復運動を前記被駆動体に行わせて、位置フィードバックの振幅及びモータトルクの振幅の相関データを取得する第1工程と、
前記第1工程において取得した前記相関データを用いて、前記位置フィードバックの振幅及び前記モータトルクの振幅の関係から前記運動伝達系に存在するバックラッシの大きさを推定する第2工程と、
を備えた送り駆動装置のバックラッシ量検知方法。 - 被駆動体と、前記被駆動体を直線的に移動駆動させる為のボールねじ機構と、前記ボールねじ機構のボールねじシャフトを回転駆動するサーボモータと、前記サーボモータを駆動制御する制御部とを有する送り駆動装置における運動伝達系に存在するバックラッシの大きさを検知するバックラッシ量検知方法であって、
前記サーボモータによって、前記ボールねじ機構を介して、周波数が変化する往復運動を前記被駆動体に行わせて、位置フィードバックの振幅及び周波数の第一相関データと、モータトルクの振幅及び周波数の第二相関データとを取得する第1工程と、
前記第1工程において取得した前記第一相関データ及び前記第二相関データを用いて前記運動伝達系に存在するバックラッシの大きさを推定する第2工程と、
を備えた送り駆動装置のバックラッシ量検知方法。 - 請求項1の発明において、前記第1工程においては周波数が一定で且つ振幅が徐々に変化する前記往復運動を前記被駆動体に行わせ、前記第2工程においては前記モータトルクの振幅の変化率が所定の値と等しい又は所定の値より大きいときの前記位置フィードバックの振幅をバックラッシの大きさとして推定する送り駆動装置のバックラッシ量検知方法。
- 請求項2の発明において、前記第1工程においては振幅が一定で且つ周波数が徐々に変化する前記往復運動を前記被駆動体に行わせ、前記第2工程においては、前記モータトルクの振幅が摩擦トルクと同値又は摩擦トルクより大きい値となる周波数のうち、前記モータトルクの振幅が極大となる周波数である第一周波数を求め、前記第一周波数と同値又は前記第一周波数よりも大きい周波数のうち、前記モータトルクの振幅が最小となる周波数である第二周波数における前記位置フィードバックの振幅をバックラッシの大きさとして推定する送り駆動装置のバックラッシ量検知方法。
- 請求項1乃至4のいずれか1の発明において、前記第1工程において前記運動伝達系に存在する摩擦力よりも大きい慣性力が発生する条件下で前記往復運動を前記被駆動体に行わせる送り駆動装置のバックラッシ量検知方法。
- 被駆動体と、前記被駆動体を直線的に移動駆動させる為のボールねじ機構と、前記ボールねじ機構のボールねじシャフトを回転駆動するサーボモータと、前記サーボモータを駆動制御する制御部とを有する送り駆動装置における運動伝達系に存在するバックラッシの大きさを検知するバックラッシ量検知装置であって、
前記制御部に前記サーボモータを駆動制御させることで、振幅が変化する往復運動を前記ボールねじ機構を介して前記被駆動体に行わせて、位置フィードバックの振幅及びモータトルクの振幅の相関データを取得するデータ取得部と、
前記データ取得部が取得した前記相関データを用いて、前記位置フィードバックの振幅及び前記モータトルクの振幅の関係から前記運動伝達系に存在するバックラッシの大きさを推定するバックラッシ量演算部と、
を備えた送り駆動装置のバックラッシ量検知装置。 - 被駆動体と、前記被駆動体を直線的に移動駆動させる為のボールねじ機構と、前記ボールねじ機構のボールねじシャフトを回転駆動するサーボモータと、前記サーボモータを駆動制御する制御部とを有する送り駆動装置における運動伝達系に存在するバックラッシの大きさを検知するバックラッシ量検知装置であって、
前記制御部に前記サーボモータを駆動制御させることで、周波数が変化する往復運動を前記ボールねじ機構を介して前記被駆動体に行わせて、位置フィードバックの振幅及び周波数の第一相関データと、モータトルクの振幅及び周波数の第二相関データとを取得するデータ取得部と、
前記データ取得部が取得した前記第一相関データ及び前記第二相関データを用いて前記運動伝達系に存在するバックラッシの大きさを推定するバックラッシ量演算部と、
を備えた送り駆動装置のバックラッシ量検知装置。 - 請求項6の発明において、前記データ取得部は、前記制御部にサーボモータを駆動制御させることで、周波数が一定で且つ振幅が徐々に変化する前記往復運動を前記ボールねじ機構を介して前記被駆動体に行わせて前記相関データを取得し、
前記バックラッシ量演算部は、前記データ取得部が取得した前記相関データに基づいて、前記モータトルクの振幅の変化率が所定の値と等しい又は所定の値より大きいときの前記位置フィードバックの振幅をバックラッシの大きさとして推定する送り駆動装置のバックラッシ量検知装置。 - 請求項7の発明において、前記データ取得部は、振幅が一定で且つ周波数が徐々に変化する前記往復運動を前記被駆動体に行わせて前記第一相関データ及び前記第二相関データを取得し、
前記バックラッシ量演算部は、
前記データ取得部が取得した前記第二相関データに基づいて、前記モータトルクの振幅が摩擦トルクと同値又は摩擦トルクより大きい値となる周波数のうち、前記モータトルクの振幅が極大となる周波数である第一周波数を求める第一周波数決定部と、
前記データ取得部が取得した前記第二相関データに基づいて、前記第一周波数と同値又は前記第一周波数よりも大きい周波数のうち、前記モータトルクの振幅が最小となる周波数である第二周波数を求める第二周波数決定部と、
前記データ取得部が取得した前記第一相関データから、前記第二周波数決定部が求めた前記第二周波数のときの前記位置フィードバックの振幅をバックラッシの大きさとして推定する推定部とを備えた送り駆動装置のバックラッシ量検知装置。 - 請求項6乃至9のいずれか1の発明において、前記データ取得部は、前記運動伝達系に存在する摩擦力よりも大きい慣性力が発生する条件下で前記往復運動を前記被駆動体に行わせてデータを取得する送り駆動装置のバックラッシ量検知装置。
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