CN101820203B - Hybrid drive semi-closed loop precision positioning system - Google Patents

Abstract

The invention discloses a combined drive semi-closed loop precision positioning system, comprising a sliding table base, wherein a linear slide rail is mounted on the sliding table base and is provided with a sliding table, the left side and the right side of the linear slide rail are respectively provided with an ultrasound wave motor driving the sliding table to move on the slide rail and a stepping motor, and the ultrasound wave motor is connected with a corner measurement device. The invention has reasonable structure, overcomes the disadvantage of short service life of the ultrasound wave motor and can realize double-motor undisturbed switchover during precision positioning process.

Description

Hybrid drive semi-closed loop precision positioning system

Technical field:

The invention relates to a semi-closed-loop precision positioning system, in particular to a semi-closed-loop precision positioning system of a hybrid driving device and a novel displacement detection device.

Background technique:

Precision positioning system is one of the key technologies for precision machining and ultra-precision machining. In order to meet the application requirements, the precision positioning system must have the performance of high frequency response, large stroke and high precision. In industrial production, to achieve linear precision movement, stepper motors are often used to drive through screw rods. However, the subdivision driving accuracy of the stepping motor depends on factors such as the subdivision current control accuracy. The larger the subdivision number, the more difficult it is to control the accuracy, and the cost of the driver is high; There is very serious high-frequency electromagnetic interference to the subdivision drive circuit due to arc stabilization and arc stabilization.

Ultrasonic motor (USM for short) is completely different in principle and structure from traditional electromagnetic motors. It has no winding and magnetic field components. It does not transfer energy through electromagnetic interaction, but directly converts electromechanical energy from piezoelectric ceramic materials. The new motor has simple structure, large output per unit volume, excellent response performance, etc., and can achieve high positioning accuracy that cannot be matched by traditional electromagnetic motors. However, the USM transmits the driving force through the direct friction coupling between the stator and the rotor. Under the action of alternating stress and friction, the motor will suffer from fatigue damage, which will easily cause the condensation layer between the stator and the piezoelectric ceramic to fall off locally, and the temperature rises rapidly, resulting in heat loss. Matching, affect the motor output torque and positioning accuracy. Moreover, the life of the USM is greatly reduced due to the sudden destruction caused by the crack initiation, expansion and instability of piezoelectric ceramics. In recent years, there are more and more systems using ultrasonic motors as precision positioning drive components, but the shortcoming of the system's short life cannot be overcome by using a single ultrasonic motor.

In recent years, scholars at home and abroad have used electromagnetic servo motors as the coarse positioning drive components of the positioning system, and ultrasonic motors or piezoelectric actuators as the precise positioning drive components of the positioning system, fully combining the respective advantages of ultrasonic motors and electromagnetic motors, and achieved good results. Effect. However, the structure of the existing hybrid drive system is complex, and the processing of the connecting parts is difficult, so it is impossible to realize the non-disturbance switching. Moreover, the precision positioning displacement detection device in the closed-loop system often uses high-precision grating scales, encoders, laser sensors, etc., which are high in cost, complex in equipment, and poor in anti-interference ability. The present invention proposes a precision positioning system based on a double-motor non-disturbance switching hybrid drive mechanism and a new type of displacement detection device. Semi-closed-loop system for high-precision displacement detection.

Invention content:

The purpose of the present invention is to provide a semi-closed-loop precision positioning system with a reasonable structure and overcome the shortcoming of the short service life of the ultrasonic motor.

Technical solution of the present invention is:

A hybrid drive semi-closed-loop precision positioning system is characterized in that it includes a slide base, a linear sliding guide rail is mounted on the slide base, a slide table is installed on the linear slide guide rail, and driving slide tables are respectively arranged on the left and right sides of the linear slide guide rail. An ultrasonic motor and a stepping motor move upward, and the ultrasonic motor is connected with an angle measuring device.

The ultrasonic motor is connected to the ball screw connected to the sliding table through the first elastic diaphragm coupling, and the ball nut is installed on the ball screw; the stepper motor is connected to the coupling supported by the bearing through the second elastic diaphragm coupling. The coupling shaft is connected with the ball nut, the ball nut is fixedly connected with the nut seat through the angular contact bearing, and the nut seat is fixedly connected with the slide table.

The ultrasonic motor and the first motor bracket are fastened and connected by screws, the first motor bracket is fixedly connected with the bearing seat of the screw support bearing, and the bearing seat of the screw support bearing is fixedly connected with the base of the slide table; the stepper motor is connected with the second motor support Fixedly connected, the second motor bracket is fixedly connected with the slide table.

The angular position measuring device includes a first turntable and a second turntable, the first turntable is concentrically connected with the output shaft of the ultrasonic motor, the second turntable is concentrically connected with the micro synchronous motor, the second turntable rotates with the micro synchronous motor, the micro synchronous motor and the ultrasonic motor The axis line of the infrared emission tube is on the same horizontal line, the first turntable and the second turntable are concentric, the infrared emitting tube is fixedly installed on the first turntable, and the projection of the central axis of the infrared beam of the infrared emitting tube on the first turntable passes through the first turntable The center of the circle, the infrared receiving tube is fixedly installed on the second turntable, the projection of the central axis of the infrared receiving tube on the second turntable passes through the center of the second turntable, the distance between the infrared receiving tube and the center of the second turntable is greater than that between the infrared emitting tube and the first The distance between the center of the turntable and the included angle between the central axis of the infrared emitting tube and the first turntable are equal to the included angle between the central axis of the infrared receiving tube and the second turntable.

The motor control system adopts the form of FPGA-assisted single-chip microcomputer, and controls the ultrasonic motor and the stepper motor driver through the PWM wave sent by the FPGA. The control modules are jointly determined.

The interface circuit of the angular displacement detection device adopts the form of FPGA-assisted single-chip microcomputer. The output signal of the infrared receiving tube is converted into a pulse by the comparator, and the adjacent output pulse is distinguished by the parity module, and the adjacent pulse is completed by the counter and the latch. For the calculation and latching of the time interval, the subtractor completes the calculation of the difference between the time intervals of two adjacent pulses, and the calculation results are sent to the single-chip microcomputer for processing to obtain the angular displacement.

The invention has reasonable structure, overcomes the shortcoming of short service life of the ultrasonic motor, and the beneficial effects are mainly manifested in:

1. Make full use of the respective advantages of the electromagnetic motor and the ultrasonic motor, overcome the shortcomings of the short life of the ultrasonic motor, and realize the long life of the system and the precise positioning of the large stroke.

2. The new hybrid drive mechanism provided can realize the non-disturbance switching of the two motors. The two motors can work simultaneously or independently. When the two motors move at the same time, the fast movement and slow adjustment of the sliding table can be realized, and the controllable precision is high.

3. Due to the short transmission hinge and simple structure, the positioning accuracy and repeat positioning accuracy of the slide table are high.

4. The provided hybrid driving mechanism has a simple structure and is easy to process.

5. A new type of angular displacement detection device is provided, which converts small angular displacement detection into linear displacement detection. The device has high precision, high resolution, low cost, easy installation, and has the advantages of no need for zero adjustment before measurement. It can realize the closed-loop control of the ultrasonic motor during the micro-feed of the positioning system.

Description of drawings:

The present invention will be further described below in conjunction with drawings and embodiments.

Fig. 1 is a structural diagram of an embodiment of the present invention.

FIG. 2 is a top view of FIG. 1 .

Fig. 3 is a structural diagram of the angular displacement measuring device of the present invention.

Fig. 4 is a measurement principle diagram of the angular displacement device of the present invention.

Fig. 5 is a timing diagram of angular displacement detection in the present invention.

Fig. 6 is a drive control circuit diagram of the precision positioning system of the present invention.

Detailed ways:

A mixed-drive semi-closed-loop precision positioning system, comprising a slide table base 1, a linear slide guide rail 2 mounted on the slide table base, a slide table 3 mounted on the linear slide guide rail, drive slide tables are respectively arranged on the left and right sides of the linear slide guide rail on the slide guide rail The moving ultrasonic motor 4 and the stepper motor 5 are connected with the angular position measuring device 6 .

The ultrasonic motor is connected to the ball screw 8 connected to the slide table through the first elastic diaphragm coupling 7, and the ball nut 11 is mounted on the ball screw; The shaft coupling 10 is connected, the shaft coupling is connected with the ball nut 11, the ball nut is fixedly connected with the nut seat through two angular contact bearings 12 with the same height of the inner and outer rings, the nut seat is fixedly connected with the sliding table 3, and is positioned by the positioning pin.

The ultrasonic motor 4 and the first motor bracket 13 are fastened and connected by screws, the first motor bracket is fixedly connected with the bearing seat 15 of the screw support bearing (angular contact bearing) 14, and the bearing seat of the screw support bearing is fixed to the slide base 1 Connection; the stepping motor 5 is fixedly connected with the second motor bracket 16, and the second motor bracket is fixedly connected with the slide table 3.

The angular position measuring device 6 comprises a first turntable 17 and a second turntable 18, the first turntable is concentrically connected with the output shaft of the ultrasonic motor, the second turntable is concentrically connected with the micro synchronous motor 19, the second turntable rotates with the micro synchronous motor, and the micro synchronous The axes of the motor and the ultrasonic motor are on the same horizontal line, the first turntable and the second turntable are concentric, the infrared emission tube 20 is fixedly installed on the first turntable, and the central axis of the infrared beam of the infrared emission tube is on the first turntable The projection passes through the center of the first turntable, and the infrared receiving tube 21 is fixedly installed on the second turntable. The projection of the central axis of the infrared receiving tube on the second turntable passes through the center of the second turntable. The distance between the infrared receiving tube and the center of the second turntable is greater than The distance between the infrared emitting tube and the center of the first turntable, the included angle (acute angle) between the central axis of the infrared emitting tube and the first turntable is equal to the included angle (acute angle) between the central axis of the infrared receiving tube and the second turntable.

The motor control system adopts the form of FPGA-assisted single-chip microcomputer, and controls the ultrasonic motor and the stepper motor driver through the PWM wave sent by the FPGA. The control modules are jointly determined.

The interface circuit of the angular displacement detection device adopts the form of FPGA-assisted single-chip microcomputer. The output signal of the infrared receiving tube is converted into a pulse by the comparator, and the adjacent output pulse is distinguished by the parity module, and the adjacent pulse is completed by the counter and the latch. For the calculation and latching of the time interval, the subtractor completes the calculation of the difference between the time intervals of two adjacent pulses, and the calculation results are sent to the single-chip microcomputer for processing to obtain the angular displacement.

The sliding table can be driven by a single ultrasonic motor and a single stepper motor, or it can be driven by two motors at the same time. When the two motors move at the same time, the fast movement and slow adjustment of the sliding table can be realized, and the fast movement and slow adjustment can only be done by changing the rotation direction of the motor.

The proposed precision positioning mechanism can be further expanded into a cross slide to realize two-free precision positioning on a plane. During specific implementation, the mechanism with another degree of freedom can be completely consistent with the mechanism proposed by the present invention.

Principle Analysis and Performance Analysis of Angular Displacement Measurement

Principle analysis

In the embodiment, a traveling-wave ultrasonic motor is used as the driving motor for precise positioning of the platform. One end of the output shaft of the ultrasonic motor is connected to the elastic coupling, and the other end is concentrically connected to the first turntable (see FIG. 3 ). The projection of the central axis of the infrared beam on the first turntable passes through the center of the first turntable. The second turntable is concentrically connected with the miniature synchronous motor and rotates together with the synchronous motor. Keep the axes of the synchronous motor and the ultrasonic motor on a horizontal line, and keep the two turntables concentric. The infrared receiving tube is fixedly installed on the second turntable and moves synchronously with the synchronous motor. The projection of the central axis of the infrared receiving tube on the falling turntable passes through the center of the second turntable. The distance between the infrared receiving tube and the center of the circle is greater than the distance between the infrared emitting tube and the center of the circle, and the included angle (acute angle) between the central axis of the infrared emitting tube and the first turntable is equal to the included angle (acute angle) between the central axis of the infrared receiving tube and the second turntable.

When measuring, keep the micro synchronous motor rotating at a constant speed (set the speed as Nr/min), and keep the micro synchronous motor turning the same as the ultrasonic motor turning. When the infrared receiving tube receives the infrared light emitted by the transmitting tube, the interface circuit outputs a high-level pulse signal, and the synchronous motor outputs a pulse signal for each rotation of the ultrasonic motor. When the ultrasonic motor is stationary, assuming that the infrared emitting tube is at position A, the receiving tube passes through the interface circuit and outputs the pulse signal as shown in Figure 5. A, the pulse interval time is the time t1 required for the synchronous motor to make one revolution. If the interface circuit controller judges that the interval between two adjacent pulses is always t1, it can be considered that the ultrasonic motor is stationary.

If the ultrasonic motor produces a slight displacement, set the direction of the displacement to be in phase with the rotation direction of the synchronous motor (both are clockwise). For the convenience of illustration, the displacement is amplified as shown in Figure 4. At this time, the photoelectric emission tube follows the rotation from the initial position A to to position B. The output signal of the receiving circuit is shown in B in Figure 5 . If the interface circuit controller judges that the interval between two adjacent pulses appears from t1 to t2 each time, it is considered that the ultrasonic motor has rotated a certain angle θ ₁ clockwise, and the size of θ ₁ is proportional to (t ₂ -t ₁ ). Available:

For example, when the photoelectric emission tube is still at position B, the output signal of the receiving circuit is shown as C in Fig. 5 . Similarly, when the ultrasonic motor continues to rotate and turns from position B to position C, the output signal of the receiving circuit is shown as D in Figure 5 . If the interface circuit controller judges that the interval between two adjacent pulses is changed from t1 to t3 each time, it is considered that the ultrasonic motor has rotated a certain angle θ ₂ clockwise, and the size of θ ₂ is proportional to (t ₃ -t ₁ ). Available:

Then the cumulative rotation angle of the ultrasonic motor is θ ₁ +θ ₂ .

2.2 Performance analysis

During specific implementation, the ultrasonic motor can be operated in a continuous running state or a stepping state. When the ultrasonic motor works in a continuous running state, the detection device cannot respond immediately after the angular displacement occurs, but can only respond when the infrared receiving tube is turned to the position opposite to the infrared emitting tube. Large positioning errors. When the ultrasonic motor is working in the stepping state, it can stop the motor every time it runs a microstep, and then run the next microstep after the angular displacement detection is completed. Since the micro-stepping angle of the traveling wave ultrasonic motor is very small during stepping operation, it can achieve high positioning accuracy.

The advantages of the new angular displacement detection device are as follows:

(1) The small angular displacement is amplified into an observable and measurable line (arc length) displacement, and the detection is completed by the method of controller timing.

(2) Simple structure, convenient installation and low cost.

(3) The measurement accuracy and resolution are high.

(4) There is no need for zero adjustment before measurement.

The sensor also has certain errors:

(1) The digital controller adopts the method of counting to realize timing, and the resolution of counting affects the accuracy of the result.

(2) The pulsation of the speed of the synchronous motor causes the uneven speed, which causes random errors.

(3) During processing and installation, the two turntables are not concentric, the motor shaft and the turntable are not concentric, and the inaccurate installation angle of the infrared receiver and transmitter will cause random errors and system errors.

Design of dual-motor drive control circuit for precision positioning system

In the embodiment, the traveling wave ultrasonic motor USR60 of Shinsei Company and the TSS103N173 four-phase stepper motor of TAMAGAWASEIKI CO.LTD Company are the system drive motors. The drive control circuit of the precision positioning system is shown in Figure 6.

The invention adopts the form of FPGA-assisted single-chip microcomputer, and in the semi-closed-loop precision positioning control process of double motors, the single-chip microcomputer intervenes less, greatly reducing the burden of the main controller. Moreover, FPGA has functions that are easy to modify, can be programmed online, and has strong versatility; the interface is simple, the response speed is fast, and it is suitable for full digital control, which can greatly improve system performance.

In Figure 6, the traveling wave ultrasonic motor works in a stepping state, and the PWM wave sent by the FPGA controls the motor driver D6060 to realize the micro-stepping of the ultrasonic motor. The prescaler module is used to control the start and stop of the motor and generate the global clock signal of FPGA; the digital setting control module is used to adjust the micro-step conduction time of the motor; the counting control module determines the PWM cycle according to the output value of the digital setting control module; the comparison control The module determines the conduction time of the micro-step and the stop time between steps; the interlock circuit is used to prevent the trigger competition of the D6060 interface and is used for the selection of the forward and reverse control of the motor. The comparison control module 2 is used to provide PWM pulses to the stepper motor and control the forward and reverse rotation of the stepper motor. The ring pulse generator is used to change the output pulse of the comparison control module 2 into a pulse train with a certain time sequence, and after power amplification Drive the stepper motor.

Prescaler module

This module uses the external clock (25M active crystal oscillator is adopted in this embodiment) as the global clock pulse and as the trigger signal of the comparison control module and the clock signal of the counter.

digital control module

The output of the counting control module is used as the counting initial value of the subsequent counting control module to adjust the step conduction time. Among them, the clk1 and updown signals are connected to the I/O port of the single-chip microcomputer, and updown is the addition and subtraction control terminal. When the updown is low, the value of the output port INIOUT is reduced by one every time the single-chip microcomputer sends a pulse from clk1; when the updown is high , the value of INIOUT is increased by one every time the microcontroller sends a pulse from clk1. The single-chip microcomputer is used to change the micro-step conduction time of the ultrasonic motor by changing the output value of the module, so that the positioning accuracy of the motor can be adjusted conveniently and the speed can be adjusted. CLK1 can be generated by the PCA module of the microcontroller.

Counting Control Module

The counting control module adjusts the conduction time of the micro-step according to the output of the counting control module, and generates a fixed stop time between steps. INIOUT is the output data of the set number control module. The module takes INIOUT as the base, and on this basis, counts up with the clock pulse provided by the prescaler module. It is automatically cleared after overflow.

Compare Control Module 1

The comparison control module 1 outputs PWM pulses with variable micro-step conduction time and fixed inter-step stop time. The comparison calculation is triggered on the rising edge of the clk3 pulse. DATAA is the input data of the counting controller module, which is compared with the built-in pulse inversion comparison value countq_temp in the Compare module to determine the inversion of the output level. CWC is the motor steering control signal. When CWC is high level, the CW signal is valid, and the motor rotates forward, otherwise it reverses.

Forward and reverse interlock module

This module is used to solve the problem that the motor turns indefinitely due to the simultaneous high level at the forward and reverse control terminals of the driver D6060.

Compare Control Module 2

The comparison control module 2 outputs a PWM pulse with an adjustable duty cycle, which is used to control the stepping motor. The ON/OFF ends of the comparison control module 1 and the comparison control module 2 are controlled by a single-chip microcomputer, so that the two motors work in time-sharing. The CW/CCW terminal is used to control the ring pulse generator to output pulse trains with different phase sequences to control the direction of the stepping motor. Since a four-phase stepping motor is used in the embodiment, the driving of the stepping motor is realized through the L298H bridge integrated drive module.

Interface Circuit Design of Angle Displacement Sensor

When the phototransmitter is opposite to the photoreceiver, the photocurrent is converted into a voltage by the resistance and passes through the comparator to output a high-level pulse. The pulse is sent to the parity check module. If the number of pulses accumulated by the module is an odd number, the ODD terminal outputs a high-level pulse. Conversely, if the number of pulses accumulated by the module is an even number, the EVEN terminal outputs a high level pulse. The rising edge of the pulse output by the ODD port makes the counter 1 module start counting, and the counter 2 module stops counting. It ensures that the initial value of the counter is zero when counting, and through the delay function of the delay module, the arrival time of the CLR signal is earlier than the arrival time of the ON signal at the start counting terminal.

The rising edge of the pulse output by the EVEN port makes the counter 2 module start counting at the same time, so that the counter 2 module stops counting. Through the delay function of the delay module, the CLR signal arrives before the ON signal of the start counting terminal, which ensures that the initial value of the counter is zero when counting.

该时间间隔可以保证同步电机带动光电接收管完成响应。当减法运算完成后由FPGA通知单片机取数，单片机通过口线读入32位二进制结果。单片机将读入的减法器输出量乘以计数器1(计数器2)的CLK脉冲周期，得到相邻脉冲间隔时间的差值，并由公式1计算出角位移。The output signals of counter 1 and counter 2 are latched by the latch, and the latch signal is provided by the parity pulse discrimination module. The pulse output by the ODD port provides a latch signal for the latch corresponding to counter 2, and the EVEN port corresponds to counter 1. The latch provides the latch signal. The subtraction operation of the output signals of the two latches is completed by the subtractor. The operation start signal is provided by the single-chip microcomputer. The time interval for starting the operation is controlled by the single-chip microcomputer. The time interval can be adjusted by the single-chip section according to the sensor response speed. The pulse signal sent by the ODD terminal can also be directly sent to the single-chip IO interface. After the single-chip computer judges that the number of pulses represented by the adjacent time interval has been latched into the double latch, it sends a subtraction operation start command. Due to the slow response speed of the sensor, it can only respond when the infrared receiving tube is turned to the position opposite to the infrared emitting tube. In order to avoid the situation that the sensor has not responded and the counter overflows, the counter must be provided with sufficient capacity. In the embodiment, a 25M source crystal oscillator is used as an external clock, and a 32-bit counter is used, and the time used for the full count is:

This time interval can ensure that the synchronous motor drives the photoelectric receiving tube to complete the response. When the subtraction operation is completed, the FPGA notifies the single-chip microcomputer to fetch the number, and the single-chip microcomputer reads the 32-bit binary result through the port line. The microcontroller multiplies the output of the subtractor read in by the CLK pulse period of counter 1 (counter 2) to obtain the difference between adjacent pulse intervals, and calculate the angular displacement by formula 1.

Claims (5)

1. A hybrid drive semi-closed-loop precision positioning system, characterized in that it includes a slide base, a linear slide guide is mounted on the slide base, a slide is mounted on the linear slide guide, and drive slides are respectively set on the left and right sides of the linear slide guide. The traveling wave ultrasonic motor and the four-phase stepping motor moving on the sliding guide rail, the ultrasonic motor is connected with the angular displacement detection device; the ultrasonic motor is connected with the ball screw connected with the sliding table through the first elastic diaphragm coupling, and the ball screw The ball nut is installed on the top; the stepper motor is connected to the coupling supported by the bearing through the second elastic diaphragm coupling, the coupling is connected to the ball nut, the ball nut is fixedly connected to the nut seat through the angular contact bearing, and the nut seat is fixed to the slide table connect. 2. The hybrid drive semi-closed-loop precision positioning system according to claim 1, characterized in that: the ultrasonic motor and the first motor bracket are fastened and connected by screws, the first motor bracket is fixedly connected with the bearing seat of the screw rod support bearing, and the wire The bearing seat of the rod support bearing is fixedly connected with the base of the slide table; the stepping motor is fixedly connected with the second motor support, and the second motor support is fixedly connected with the slide table. 3. The hybrid drive semi-closed-loop precision positioning system according to claim 1 or 2, characterized in that: the angular displacement detection device includes a first turntable and a second turntable, the first turntable is concentrically connected with the output shaft of the ultrasonic motor, and the second turntable Connected concentrically with the micro synchronous motor, the second turntable rotates with the micro synchronous motor, the axes of the micro synchronous motor and the ultrasonic motor are on the same horizontal line, the first turntable and the second turntable are concentric, and the infrared emitting tube is fixedly installed on the On the first turntable, the projection of the central axis of the infrared beam of the infrared emitting tube on the first turntable passes through the center of the first turntable, the infrared receiving tube is fixedly installed on the second turntable, and the projection of the central axis of the infrared receiving tube on the second turntable passes through The center of the second turntable, the distance between the infrared receiving tube and the center of the second turntable is greater than the distance between the infrared emitting tube and the center of the first turntable, and the angle between the central axis of the infrared emitting tube and the first turntable is equal to the central axis of the infrared receiving tube and the second turntable. The included angle of the turntable. 4. The hybrid drive semi-closed-loop precision positioning system according to claim 1 or 2 is characterized in that: the motor control system adopts the form of an FPGA-assisted single-chip microcomputer, and the PWM wave sent by the FPGA controls the ultrasonic motor and the stepper motor driver, and the PWM wave The cycle is controlled by the comparison control module, and the PWM duty cycle is jointly determined by the comparison control module, the count control module and the number setting control module. 5. The hybrid drive semi-closed-loop precision positioning system according to claim 1 or 2, is characterized in that: the interface circuit of the angular displacement detection device adopts the form of an FPGA-assisted single-chip microcomputer, and the output signal of the infrared receiving tube is converted into a pulse by a comparator, The parity check module completes the distinction of adjacent output pulses, the counter and latch complete the calculation and latching of the time interval of adjacent pulses, and the subtractor completes the calculation of the difference between the time intervals of two adjacent pulses, and the calculation result Send the single-chip microcomputer to process to get the size of the angular displacement.

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