JP5041327B2 - Power steering control device and method - Google Patents

Description

  The present invention relates to a power steering control device and method capable of performing offset correction of a detected current.

  As an auxiliary steering device for an automobile, an electric power steering device using the torque of an electric motor is used. This power steering device includes a torque sensor that detects a steering operation by a driver, a power steering control device (ECU) that calculates an auxiliary steering force based on a detection signal from the torque sensor, and a rotational torque based on an output signal from the ECU. And an electric motor that generates the torque and a reduction gear that transmits the rotational torque to the steering mechanism.

  The above-described ECU is configured as shown in FIG. 7, for example. In this figure, ECU 90 receives signals from torque sensor 91 and vehicle speed sensor 92, and ECU 90 has a function of controlling electric motor 93 based on these signals. The ECU 90 includes a current command value calculation unit 901, an adder 902, a current control unit 903, a drive circuit 904, and a current detection circuit 905. The current command value calculation unit 901 calculates a current command value I based on signals from the torque sensor 91 and the vehicle speed sensor 92. The adder 903 calculates a deviation current ΔI between the current value command value I and the detection current i detected by the current detection circuit 905, and the current control unit 903 has a motor control signal such that the error current ΔI becomes zero. It is for calculating. The motor drive circuit 904 has a function of supplying a three-phase current to the electric motor 93 based on the motor control signal. The current detection circuit 905 has two current sensors, and detects the other two current values based on one of the three-phase currents. The detected current i is input to the adder 902 as a negative signal.

  In the ECU 90 configured as described above, negative feedback control is performed so that the detected current i becomes equal to the current command value I. However, when an error exists in the detection system such as the current detection circuit 905, the error appears as it is in the three-phase current. If there is an error in the offset current or the detection gain in the two current sensors constituting the current detection circuit 905, an error occurs in each current value of the three-phase current output from the drive circuit 904. As a result, the electric motor 93 Torque ripple will occur. Such torque ripple adversely affects handle feeling and the like. In particular, in recent high-output type power steering devices, as the drive current increases in capacity, the effect of the offset current may appear to the extent that it can be experienced.

  In order to avoid such a problem, offset measurement and adjustment are performed for each power steering device at the time of factory shipment. However, even if the offset adjustment is performed at the time of shipment from the factory, the offset error changes due to a temperature change or a secular change, and correct offset correction cannot always be performed. For this reason, attempts have been made to automatically execute offset correction by detecting an offset current during the assist operation or during the initialization process. However, during the assist operation, the current value detected by the current detection circuit includes not only the offset current but also the component of the drive current, so that it is difficult to accurately detect only the offset current.

  As a conventional technique for solving the above-described problem, for example, a power steering control device described in Japanese Patent Laid-Open No. 2003-312492 has been devised. This device attempts to detect an offset current by storing a residual magnetic flux in a state where no current is passed through a Hall element type non-contact current sensor. However, when the current value output from the current sensor includes both components of the offset current and the drive current, it is not possible to detect only the offset current, and it is not possible to perform offset correction during the assist operation. . Further, this apparatus only detects the offset of the current sensor, and cannot correct the offset existing in the amplification circuit of the detection signal.

Furthermore, as another conventional technique, an electric power steering control device described in JP-A-2002-234457 has been devised. This publication discloses an apparatus for monitoring a drive system abnormality by comparing an estimated motor current value with an actual motor current value. However, this apparatus does not calculate the difference between the estimated motor current value and the estimated motor current value in order to detect the offset current, but has a different purpose from the present invention. In this reference, a high-frequency current is passed at the time of initial diagnosis, but it is not intended to remove the influence of the model error between the motor and the nominal model as in the present invention.
JP 2000-234457 A JP 2003-312492 A

  The present invention has been made in view of the above-described problems, and a problem to be solved by the present invention is a power steering control device capable of accurately detecting an offset current due to aging, temperature drift, and the like, and It is to provide a method.

  In order to solve the above-described problems, the present invention provides a power steering control device for driving a motor for generating steering assist torque based on a steering torque applied to a steering, and detects a drive current in the motor. A current detection means for outputting a current detection value; a control means for calculating a current command value based on the steering torque and the current detection value; a drive means for supplying a drive voltage based on the current command value to the motor; Storage means for storing at least a nominal model representing a transfer function of the motor and the current detection means, and calculating an offset current based on a difference between the current detection value and the nominal model, and correcting the offset current Offset correction means for calculating an offset correction value.

The offset correction unit includes a low-pass filter for removing a high frequency component included in a difference between the detected current value and the nominal model.
Further, according to the present invention, at the time of starting, a high frequency voltage having an amplitude that does not rotate the motor at a frequency higher than the cutoff frequency of the low pass filter is applied to the motor.

The control means outputs a current command value having a frequency higher than the cutoff frequency of the low-pass filter at the time of starting.
Furthermore, the offset correction means calculates the offset current and the offset correction value when the detected current value is substantially zero.

  According to the present invention, a nominal model representing a motor transfer function is stored in advance, and an offset current is calculated based on the difference between the detected current value and the nominal model in the motor, thereby preventing aging and temperature drift of the motor. The resulting offset current can be detected. Further, by calculating an offset correction value based on this offset current, it is possible to perform highly accurate offset correction.

  Further, by removing the high frequency component included in the difference between the current detection value and the nominal model, the high frequency disturbance component can be removed, and the offset current can be detected with high accuracy. Furthermore, the influence of the model error between the motor and the motor nominal model can be eliminated by applying to the motor a high-frequency voltage with an amplitude that does not rotate the motor at a frequency higher than the cutoff frequency of the low-pass filter at the start. As a result, highly accurate offset correction is possible. Further, when the detected current value is substantially zero, the offset correction can be performed even during the assist operation by calculating the offset current and the offset correction value.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic diagram of an electric power steering apparatus according to the first embodiment. In this figure, a steering 61 is connected to a rack and pinion 66 via a steering shaft 62, universal joints 63 and 64, and a shaft 65. Further, the rack and pinion 66 is provided with a wheel tie rod 67, and the rotational movement of the handle 61 is converted into the axial movement of the tie rod 67.

  A torque sensor 4 is provided on the shaft 65, and the torque sensor 4 can detect a steering torque applied to the steering 61 and output a torque signal. Further, the reduction gear 31 and the motor 3 are attached to the shaft 65, and the rotational torque of the motor 3 is transmitted to the shaft 65 via the reduction gear 31.

  The ECU 1 calculates the auxiliary steering torque based on the torque signal from the torque sensor 4 and the vehicle speed signal from the vehicle speed sensor 2 as described above, and sends the drive current based on the calculation result to the motor 3. The ECU 1 is directly supplied with electric power from the power source 5 and is connected in parallel to the power source 5 via the ignition key 5a. When the ignition key 5a is turned on, the relay in the ECU 1 is turned on to supply power. It becomes the composition which is done.

  FIG. 2 is a block diagram illustrating a hardware configuration of the ECU 1. The ECU 1 includes a bus 100, a nonvolatile memory 109, an A / D converter 110, an interface 111, a clock generation circuit 112, a CPU 113, a ROM 114, a RAM 115, an RD converter 116, a PWM controller 117, a motor drive circuit 118, a motor current detection circuit 120, 121 and amplifier circuits 122 and 123.

  The bus 100 is for transmitting and receiving data among the A / D converter 110, the I / F 111, the clock generation circuit 112, the CPU 113, the ROM 114, the RAM 115, and the like. The A / D converter 110 outputs the main torque signal and the sub torque signal output from the torque sensor 4, the detected current from the motor current detection circuits 120 and 121, the motor rotation angle signal from the RD converter 116, and the voltage across the terminals of the motor 3. Input and convert to digital signal.

  The torque sensor 4 described above includes two output signals, a main torque signal and a sub torque signal, and the total voltage of these signals is set to have a cross characteristic that is a constant voltage (for example, 5 V). That is, when no torque is applied to the steering, the main torque signal and the sub torque signal are each a torque neutral voltage of 2.5 V, and when some torque is applied to the steering, the main torque signal and the sub torque signal are the neutral voltage 2 .5V changes in opposite directions with reference to 5V.

  The interface 111 counts vehicle speed pulses from the vehicle speed sensor 2 and converts them into digital signals. The ROM 114 is used as a memory for storing a control program for the motor 3, a PWM calculation program, a fail safe program, and the like, and the RAM 115 is used as a work memory for operating the program. The non-volatile memory 109 is configured by an EEPROM, a flash memory, or the like, and can hold the memory contents even after the ignition key 5a is turned off. The nonvolatile memory 109 is used for recording data such as an offset correction table described later.

  The PWM controller 117 is for converting a signal representing the torque of the motor 3 into pulse command modulated duty command values W, V, U, Wb, Vb, Ub. Here, the pulse signals W, V, and U represent positive-phase three-phase signals, and the pulse signals Wb, Vb, and Ub represent negative-phase three-phase signals.

  The motor drive circuit 118 is composed of three inverter circuits for generating a WVU three-phase current, and each inverter circuit has a switching transistor on the power supply voltage side (upper stage) and a switching transistor on the ground potential side (lower stage). ing. The normal phase duty command values W, V, and U are input to the gates of the upper switching transistors, and the negative phase duty command values Wb, Vb, and Ub are input to the lower switching transistors. That is, the upper and lower switching transistors are complementarily connected, and drive currents Iu, Iv, and Iw having desired pulse widths are generated by alternately repeating on and off operations. In order to prevent the upper switching transistor and the lower switching transistor from being turned on at the same time, the time when both of them are turned off (dead time) is the normal phase duty command value W, V, U and the reverse phase duty command value Wb. , Vb, Ub are provided before and after the on-time. In this way, by providing the dead time, it is possible to avoid a short circuit between the upper and lower switching transistors. The RD converter 116 has a function of supplying an exciting current to the resolver 31 and outputting an output signal from the resolver 31 to the A / D converter 110 as a rotation angle signal.

  The motor current detection circuits 120 and 121 are composed of current-voltage conversion elements such as resistors, and are used to detect drive currents Iu and Iw to the motor 3 and output a current detection value having a voltage corresponding to the current. is there. The detected current value is subjected to voltage fluctuation correction by a power supply voltage correction circuit (not shown) and then input to the amplifier circuits 122 and 123. Further, the current detection values amplified by the amplifier circuits 122 and 123 are input to the A / D converter 110 and converted into digital signals. That is, since the offset current in the motor current detection circuits 120 and 121 is extremely small, the offset current changes only about ± 0 to 3 LSB of the A / D converter 110. Therefore, in the present embodiment, the offset current is amplified by, for example, about 10 times by the amplifier circuits 122 and 123 and input to the A / D converter 110.

  FIG. 3 shows a functional block diagram of the ECU 1. In this figure, a current command value calculation unit 11, a current command value limiting unit 12, a vector control unit 13, an adder 14, a current control unit 15, an adder 16, an offset correction unit 20, a low pass filter 21, a motor nominal model 22, Each function of the adder 23 and the motor nominal model correction unit 24 is realized by the CPU 113.

  A main torque signal and a sub torque signal from the torque sensor 4 are input to the current command value calculation unit 11 after A / D conversion. The current command value calculation unit 11 has a function of calculating a current command value based on a torque signal and a vehicle speed signal. The current command value calculation unit 12 has handle return compensation and motor maximum current control. For example, the handle return compensation performs control for restoring the handle 61 to the neutral position. In general, in the electric power steering apparatus, the self-aligning torque tends to be weak due to the influence of the reduction gear 31 and the like, and thus the handle 61 is difficult to return to the neutral position. Therefore, by detecting the motor terminal voltage and the motor current when the motor 3 is rotated by the action of the self-aligning torque, the motor angular velocity is detected, or the motor angular velocity is detected from the angle difference of the angle sensor. It is possible to calculate a compensation current value for restoring the handle to the neutral position.

  The current command value limiting unit 12 limits the current command value based on the motor rotation speed, and the vector control unit 13 outputs a three-phase current command value representing the current command value of each phase of UVW based on the motor angle. This current command value is input to the adder 14, and negative feedback control is performed so that the detected current value matches the current command value.

  The motor current detection circuits 120 and 121 detect U-phase and W-phase currents supplied to the motor 3, and output current detection values having voltage values corresponding to the current values. The detected current value is amplified by the analog amplifier circuits 122 and 123, but may be further amplified by a multiplier after A / D conversion. The current detection value amplified in this way is input to the adder 16 and the offset correction unit 20. According to the present embodiment, it is possible to increase the resolution of the current detection value per 1 LSB by increasing the gain of the current detection value and performing the averaging process. Further, the resolution per 1 LSB of the current detection value may be increased by combining the gain increase processing and the integration processing in the current control unit 15.

The motor nominal model 22 models the transfer function of the motor 3 and represents the transfer function P _N (s) when the voltage command value V is input and the current detection value I is output. That is, the transfer function P _N (s) equivalent to the motor 3 is represented as the motor nominal model 22. The motor nominal model 22 is generated by an actual measurement value or a theoretical value of the frequency response of the motor 3 or the like.

The adder 23 calculates the difference between the output P _N (s) · V of the motor nominal model 22 and the current detection value from the current detection circuits 120 and 121 from the current detection value from the current detection circuits 120 and 121. It is. That is, from the adder 23, an output of the following equation is obtained.
I _L = (P _N (s) −P (s)) V + P (s) d + I _offset formula (1)
Here, P (s) represents the actual transfer function of the motor, and P (s) V is obtained as the current detection value I. Further, d represents a high-frequency input disturbance and includes, for example, a high-frequency component of drive torque accompanying steering. I _offset represents an offset component included in the current detection value I, and is caused by the current detection circuits 120 and 121 and the amplification circuits 122 and 123. In Formula (1), if the motor nominal model 22 accurately represents the transfer function of the motor 3 or the like, P _N (s) −P (s) = 0, and the first term on the right side of Formula (1) is zero. Thus, I _L = P (s) d + I _offset is output from the adder 23.

  The low-pass filter 21 is for removing P (s) d in the equation (1), that is, a component of high-frequency input disturbance. The low-pass filter 21 can be constituted by, for example, an IIR type or FIR type digital filter. The cutoff frequency of the low-pass filter 21 is desirably low enough to remove disturbance components. For example, it is set so that a frequency equal to or higher than the motor time constant is cut off.

As described above, the offset current is generated due to the aging and temperature change of the elements in the current detection circuits 120 and 121 and the amplifier circuits 122 and 123, and hardly contains high-frequency components. Therefore, by removing the high-frequency disturbance component P (s) d included in the detected current value by the low-pass filter 21, it is possible to extract only the offset current I _offset .

The offset correction unit 20 is for storing the I _offset extracted by the low-pass filter 21 in the correction table as an offset correction value. The adder 16 subtracts the offset correction value E for the U and W phases from the detected current value I, and outputs the detected current value I that does not include an offset component to the adder 14 that forms the feedback loop. The detected current values of the U and W phases are compared with the current command value in the adder 14, and the control deviation Δi is given to the current control unit 15. The current control unit 15 performs so-called PI control that combines proportional control and integral control based on the control deviation Δi. An output signal from the current control unit 15 is output to the drive circuit 117, and a three-phase drive current is output to the motor 3.

  The failure determination unit 18 is for performing initial diagnosis and fail-safe processing of the power steering apparatus by monitoring torque signals, power supply voltages, and the like. For example, when the failure diagnosis unit 18 detects an abnormality in the motor 3, the torque sensor 4, etc., an instruction can be given to the current command value calculation unit 11 so as to perform a gradual reduction process of the auxiliary torque.

  FIG. 4 is a block diagram of the offset correction unit 20. The offset correction unit 20 includes a correction table 200, a detection condition determination unit 201, and an offset calculation unit 202. The detection condition determination unit 201 is for detecting whether or not a condition for detecting the offset current value is satisfied, that is, a state where the motor drive current is small based on the current detection value, the motor command value, and the like. When the detection condition is satisfied, a new offset current is detected based on the current detection value.

The offset calculation unit 202 is for calculating an offset correction value based on the detected offset current _Ioffset . The offset correction value newly calculated by the offset calculation unit 202 is written in the correction table 200. At the time of offset correction, an offset correction value is read from the correction table 200, and offset correction is performed by subtracting the offset correction value from the current detection value.

In addition, the resistance of the motor changes due to aging and humidity changes. As a result, a difference occurs between the motor nominal model P _N (s) and the actual motor model P (s). In the present invention, a high-frequency voltage V having an amplitude that is higher than the cutoff frequency of the low-pass filter and does not rotate at the time of offset calculation is added. The motor nominal model correcting unit 24 observes the amplitude a of the high frequency voltage V, the amplitude b of the high frequency current I flowing through the motor by this high frequency voltage, and the phase difference φ between the high frequency voltage V and the high frequency current I, and R = a / b * Calculate the resistance value by the equation | cosφ | and correct the resistance value of the motor nominal model. Thereby, a motor nominal model can be brought close to an actual motor model.

  Next, the operation of the power steering control device according to this embodiment will be described. FIG. 5 is a main flowchart showing the operation of the power steering control device. First, when the ignition switch 5a is turned on, the ECU 1 starts its operation and executes initial settings such as initial diagnosis of the power steering device (step S51). Next, the ECU 1 sets the average value of the voltage command value V to zero and superimposes a signal higher than the cutoff frequency of the low-pass filter 21 on the voltage command value V (step S52). A high frequency driving current is applied to the motor 3 from the driving circuit 117. The applied high frequency voltage V causes a high frequency current I to flow, and the motor nominal model correction unit 24 observes the amplitude and phase difference between the high frequency current I and the high frequency voltage command value V, thereby calculating the motor resistance R. Correct the nominal model. Thereby, it becomes possible to remove the influence of the model error between the motor 3 and the motor nominal model.

The current detection values output from the current detection circuits 120 and 121 are subtracted from the motor nominal model in the adder 23, and then the high-frequency component is removed by the low-pass filter 21. The offset correction unit 20 detects the current detection value thus obtained as an offset current I _offset (step S53). The offset correction unit 20 _writes the offset correction value in the correction table 200 in the offset correction unit 20 based on the detected offset current I _offset .

  When the initial diagnosis ends normally and the ECU 1 permits the assist operation of the power steering (YES in step S54), the assist control is started (step S55). That is, the current command value calculation unit 11 calculates a current command value based on a torque signal or the like, and the vector control unit 13 outputs a three-phase current command value. The current detection circuits 120 and 121 detect a drive current to the motor 3 and output a current detection value. The current control unit 15 outputs a PWM signal to the drive circuit 117 so that the detected current value becomes equal to the current command value. The PWM drive circuit 117 supplies a three-phase drive current to the motor 3, and the auxiliary steering torque is applied to the steering 61. To be applied.

  Further, the offset correction value from the offset correction unit 20 is output to the adder 16, and the adder 16 subtracts the offset correction value from the current detection value. As a result, the offset-corrected current detection value is provided to the current control unit 15 via the adder 14.

  The offset correction unit 20 detects the offset current based on the current detection value if the offset detection condition is satisfied while monitoring the current detection value and the like (step S56). Until the ignition switch 5a is turned off (YES in step S57), the ECU 1 repeatedly executes the above-described processing.

FIG. 6 is a flowchart showing details of the above-described offset detection processing (steps S53 and S56). First, the ECU 1 acquires the current detection value output from the current detection circuits 120 and 121 (step S61). When the voltage command value is V, the current detection value at this time is represented by P (s) V + P (s) d + I _offset . Next, ECU1 determines whether or not the detection condition is satisfied (step S62). That is, the ECU 1 determines a detection condition such that the detected current value is within a predetermined range. If the detection condition is not satisfied (NO in step S62), the ECU 1 returns to the main flowchart in FIG. On the other hand, when the detection condition is satisfied (YES in step S62), ECU 1 executes the offset detection process after step S63.

In step S63, the ECU 1 acquires the motor transfer function P _N (s) from the motor nominal model 22, and calculates the current value P _N (s) V based on the transfer function P _N (s) and the voltage command value V. (Step S63). The voltage command value V represents the voltage command value given to the drive circuit 117 from the current control unit 15 at the present time. Note that a high-frequency signal may be superimposed on the voltage command value V as in the correction at the time of initial diagnosis. That is, by superimposing a high-frequency signal higher than the cutoff frequency of the low-pass filter 21 on the voltage command value V, it is possible to remove the model error between the motor and the motor nominal model.

The adder 23 subtracts the current value P _N (s) V based on the motor nominal model 22 from the current detection values of the motor detection circuits 120 and 121 (step S64). Since the motor nominal model 22 is a model of a transfer function including the motor drive circuit 117, the current detection circuits 120 and 121, and the motor 3, the first term of the above equation (1), that is, (P _N (s ) -P (s)) V is zero. For this reason, the detected current value output from the adder 23 is represented by P (s) d + I _offset .

The low-pass filter 21 removes the high frequency component P (s) d in the current detection value P (s) d + I _offset, and as a result, only the offset current _Ioffset is included in the detection current value (step S65).

The offset current I _offset thus obtained is input to the offset correction unit 20, and the offset correction unit 20 calculates an offset correction value that cancels the offset current I _offset (step S66). The offset correction value is recorded in the correction table 200, and the correction table 200 is updated (step S67). When the above processing ends, the ECU 1 returns to the main flowchart of FIG.

As described above, according to the present embodiment, the offset current can be accurately detected by subtracting the current value based on the motor nominal model 22 from the detected current value.
Moreover, since the time constant of the aging change and temperature change of the offset current has a large time constant, it is possible to extract only the component of the offset current by removing high-frequency components such as steering operation and disturbance from the current detection value. For this reason, an accurate offset current can be detected.

  Although the present embodiment has been described above, the present invention is not limited to the above-described configuration, and can be changed without departing from the spirit of the present invention. For example, the power steering control device according to the present embodiment can be applied to a hydraulic power steering device regardless of a column type or a rack type. Further, the form of the program is not limited to the above-described flowchart, and can be changed as long as the same function can be realized.

1 is a schematic diagram of a power steering apparatus according to an embodiment of the present invention. It is a block diagram of a power steering control device concerning one embodiment of the present invention. It is a functional block diagram of the power steering control device concerning one embodiment of the present invention. It is a block diagram of the offset correction part which concerns on one Embodiment of this invention. It is a main flowchart of the power steering control device concerning one embodiment of the present invention. It is a flowchart showing the detail of the offset detection process of the power steering control apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the conventional power steering control apparatus.

Explanation of symbols

1 ECU
3 Motor 4 Torque Sensor 11 Current Command Value Calculation Unit 13 Vector Control Unit 15 Current Control Unit 20 Offset Correction Unit 21 Low-Pass Filter 22 Motor Nominal Model 24 Motor Nominal Model Correction Units 120 and 121 Current Detection Circuit

Claims (10)

A power steering control device for driving a motor for generating a steering assist torque based on a steering torque applied to a steering,
Current detection means for detecting a drive current in the motor and outputting a current detection value;
Control means for calculating a current command value based on the steering torque and the current detection value;
Drive means for providing the motor with a drive voltage based on the current command value;
Storage means for storing at least a nominal model representing the transfer function of the motor;
A power steering control device comprising: an offset correction unit that calculates an offset current based on a difference between the detected current value and the nominal model, and calculates an offset correction value for correcting the offset current.   The power steering control device according to claim 1, wherein the offset correction means includes a low-pass filter for removing a high frequency component included in a difference between the detected current value and the nominal model.   The power steering control device according to claim 2, wherein the offset correction means calculates the offset current and the offset correction value at the time of starting.   4. The power steering control device according to claim 3, wherein a high-frequency voltage having an amplitude at which the motor does not rotate at a frequency higher than the cutoff frequency of the low-pass filter is applied to the motor at the time of starting.   The power steering control device according to claim 1, wherein the offset correction unit calculates the offset current and the offset correction value when the current detection value is substantially zero. A power steering control method for driving a motor for generating a steering assist torque based on a steering torque applied to a steering,
Detecting a drive current in the motor by a current detection circuit and outputting a current detection value;
Calculating a current command value based on the steering torque and the current detection value;
Providing the motor with a drive voltage based on the current command value;
Storing at least a nominal model representing a transfer function of the motor, calculating an offset current based on a difference between the detected current value and the nominal model, and calculating an offset correction value for correcting the offset current And a power steering control method.   The power steering control method according to claim 6, further comprising a step of removing a high frequency component included in a difference between the detected current value and the nominal model.   The power steering control method according to claim 7, wherein the offset current and the offset correction value are calculated at the time of starting.   9. The power steering control method according to claim 8, wherein a high frequency voltage having an amplitude at which the motor does not rotate at a frequency higher than a cutoff frequency of the low pass filter is applied to the motor at the time of starting.   The power steering control method according to claim 6, wherein the offset current and the offset correction value are calculated when the detected current value is substantially zero.

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