Bearingless motor radial displacement detection error compensation method

Abstract

The invention discloses a radial displacement detection error compensation method for a bearingless motor, which aims at solving the problem of eccentricity of a suspension position of a bearingless motor rotor caused by non-ideal factors such as process assembly errors, inconsistent device characteristics and device temperature excursion, and is used for carrying out self-adaptive compensation on eccentricity of the rotor in a suspension state of the motor. And suspension of the rotor at the optimal position (the geometric center of the stator) is realized. According to the method, the position of the rotor in the state of minimum anti-eccentric suspension current is regarded as the geometric center of the stator, the anti-eccentric suspension current of the bearingless motor is regarded as an observation object, and self-adaptive compensation of the suspension position eccentricity of the rotor of the bearingless motor is realized. The observed quantity is convenient to obtain and can be realized by designing a low-pass filtering link with simple design, the eccentricity condition of the rotor suspension position can be well reflected, the algorithm is simple to realize, and the system structure is simple.

Description

Technical Field

[0001] The invention relates to the technical field of bearingless motor driving, and in particular to a bearingless motor radial displacement detection error compensation method. Background Art

[0002] Compared with traditional mechanical bearing motors, bearingless motors have no mechanical wear and have the advantages of small size, easy maintenance, long life, and high precision. They are widely used in centrifuges, sealed pumps, semiconductor industry, life sciences, aerospace and other high-performance occasions. As an important part of the bearingless motor control system, the accuracy and real-time performance of the rotor radial displacement sensor detection link are important guarantees for the high-performance operation of the bearingless motor. However, due to the existence of non-ideal factors such as process assembly errors, inconsistent device characteristics, and device temperature drift, the center detected by the radial displacement sensor does not coincide with the geometric center of the bearingless motor stator, which is the problem of eccentricity of the rotor suspension position, which leads to additional system losses and reduced suspension performance. Therefore, for the aforementioned rotor suspension position eccentricity problem, targeted compensation measures need to be implemented to ensure the high-performance operation of the bearingless motor. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a bearingless motor radial displacement detection error compensation method in view of the defects of the background technology. Aiming at the problem of eccentricity of the bearingless motor rotor suspension position caused by non-ideal factors such as process assembly errors, inconsistent device characteristics and device temperature drift, the rotor eccentricity in the motor suspension state is adaptively compensated to achieve the suspension of the rotor in the optimal position (stator geometric center). This method considers the position of the rotor in the state of minimum anti-eccentricity suspension current as the stator geometric center, takes the anti-eccentricity suspension current of the bearingless motor as the observation object, and realizes the adaptive compensation of the eccentricity of the bearingless motor rotor suspension position. The observation quantity is easy to obtain and can be realized by designing a simple low-pass filter link, and can better reflect the eccentricity of the rotor suspension position. The algorithm is simple to implement and the system structure is simple.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

[0005] A method for compensating the radial displacement detection error of a bearingless motor is proposed. The anti-eccentricity suspension current of the bearingless motor is used as the observation object. The eccentricity of the rotor suspension position in the bearingless motor suspension state is compensated to achieve the suspension of the rotor at the optimal position (stator geometric center). The implementation steps of the scheme are as follows:

[0006] Step S1: First, actively apply the initial vector of eccentricity compensation

[0007] Step S2: Calculate the eccentricity compensation vector at the current moment

[0008] Step S3: Obtain the bearingless motor suspension current vector at the current moment And complete the suspension closed-loop control;

[0009] Step S4: The obtained bearingless motor suspension current vector Perform mathematical processing to obtain the anti-disturbance suspension current amplitude of the bearingless motor at the current moment and anti-eccentric suspension current amplitude

[0010] Step S5: Obtain the current bearingless motor tracking transformation matrix P t (k) and tracking step matrix dP xy (k);

[0011] Step S6: Repeat steps S2 to S5 to obtain the rotor eccentricity compensation vector in real time It is applied to the bearingless motor system to compensate for the eccentricity of the rotor suspension position until the rotor can run stably at the optimal point (stator geometric center).

[0012] Further, as a bearingless motor radial displacement detection error compensation method of the present invention, the eccentricity compensation initial vector in step S1 is The setting is not unique and can be set in any direction according to actual needs.

[0013] Further, as a bearingless motor radial displacement detection error compensation method of the present invention, the eccentricity compensation vector at the current moment in step S2 is The calculation method is the tracking step matrix dP obtained at the last moment xy (k-1) and the unit vector The corresponding formula can be written as

[0014] Further, as a bearingless motor radial displacement detection error compensation method of the present invention, the bearingless motor suspension current vector in step S3 The acquisition can be obtained by, but is not limited to, sampling the current sensor.

[0015] Further, as a bearingless motor radial displacement detection error compensation method of the present invention, the bearingless motor suspension closed-loop control system in step S3 can adopt but is not limited to the typical control structure of displacement outer loop-current inner loop. The basic principle is to set the radial displacement vector of the bearingless motor to Its actual sampling value Make a difference and consider the eccentricity compensation vector The function of the bearingless motor is to send it to the displacement regulator to obtain the radial suspension force setting value. Then, the suspension current vector setting value is obtained through the bearingless motor decoupling model The actual sampling value of the suspension current vector The difference is sent to the current regulator to obtain the suspension command voltage vector Finally, the inverter switching signal S is obtained through the modulation link L To achieve suspension closed-loop control of bearingless motor.

[0016] Further, as a bearingless motor radial displacement detection error compensation method of the present invention, the bearingless motor suspension current vector in step S4 can be divided into an anti-disturbance suspension current vector and anti-eccentric suspension current vector The former is used to generate the radial suspension force part to resist the external disturbance force, and the latter is used to generate the radial suspension force part to resist the eccentric magnetic pull. For the latter anti-eccentric suspension current vector, the more serious the eccentricity of the rotor suspension position, the greater the amplitude of the additional suspension current vector required to resist the eccentric magnetic pull, that is, the anti-eccentric suspension current vector amplitude is The larger the rotor suspension position is, the greater the magnitude of the anti-eccentric suspension current is. It's the smallest.

[0017] Further, as a bearingless motor radial displacement detection error compensation method of the present invention, the anti-disturbance suspension current vector in step S4 and anti-eccentric suspension current vector For the former, since the rotor of the bearingless motor is affected by a series of unknown disturbance forces, even in a stable state, the amplitude of the anti-interference suspension current is is also changing; the difference is that for the latter, the amplitude of the anti-eccentric suspension current Theoretically, it is a constant value in a stable state, that is, adding a low-pass filter link can realize the extraction of the anti-eccentric suspension current component at the current moment. The corresponding formula can be written as

[0018]

[0019] Further, as a bearingless motor radial displacement detection error compensation method of the present invention, the bearingless motor tracking step matrix dP at the current moment in step S5 is xy (k) is determined by the quadrant of the rotating coordinate system where the anti-eccentric suspension vector difference between the current moment and the previous moment is located, where the tracking step matrix dP xy and tracking transformation matrix P t Both are 2×2 matrices.

[0020] Furthermore, as a bearingless motor radial displacement detection error compensation method of the present invention, in order to prevent the bearingless motor suspension position from fluctuating at the optimal point, the compensation method, when tracking the minimum anti-eccentricity suspension current vector amplitude, the eccentricity compensation vector The rotor fluctuates back and forth at the optimal point, causing the rotor to fluctuate even in a stable state. A counting threshold c is set. Th ;Each eccentricity compensation vector The fluctuations will be recorded in the fluctuation count value c. When the fluctuation count value c is greater than the counting threshold c Th When the proposed rotor suspension position eccentricity compensation method stops, that is, the bearingless motor tracking step matrix dP at the current moment xy (k) is 0.

[0021] Furthermore, as a bearingless motor radial displacement detection error compensation method of the present invention, in step S5, in order to ensure that the proposed suspension position eccentricity compensation method can be restarted normally when the rotor suspension position eccentricity problem occurs again, a compensation current threshold i is set. Th , the current amplitude of the anti-eccentric suspension current at the current moment Greater than the minimum value of the anti-eccentric suspension current amplitude during the algorithm operation , the proposed suspension position eccentricity compensation method will restart.

[0022] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0023] 1. The present invention provides a bearingless motor radial displacement detection error compensation method, which can adaptively compensate for the rotor eccentricity in the motor suspension state, and realize the suspension of the rotor at the optimal position (stator geometric center), aiming at the problem of eccentricity of the bearingless motor rotor suspension position caused by non-ideal factors such as process assembly error, inconsistent device characteristics and device temperature drift;

[0024] 2. The present invention provides a bearingless motor radial displacement detection error compensation method, wherein the selected observation quantity, the bearingless motor anti-eccentricity suspension current, is easy to obtain and can better reflect the rotor eccentricity;

[0025] 3. The present invention provides a bearingless motor radial displacement detection error compensation method. The proposed method algorithm is simple to implement, does not need to rely on any parameters, and has a simple system structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart of a bearingless motor radial displacement detection error compensation method according to the present invention;

[0027] Figure 2 This is the selection rule of the tracking transformation matrix of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0029] The present invention may be implemented in many different forms and should not be considered limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0030] The present invention discloses a method for compensating the radial displacement detection error of a bearingless motor. In order to solve the problem of eccentricity of the rotor suspension position of a bearingless motor caused by non-ideal factors such as process assembly errors, inconsistent device characteristics, and device temperature drift, the rotor eccentricity in the motor suspension state is adaptively compensated to achieve suspension of the rotor at the optimal position (geometric center of the stator). This method considers the position of the rotor in the state of minimum anti-eccentricity suspension current as the geometric center of the stator, takes the anti-eccentricity suspension current of the bearingless motor as the observation object, and realizes adaptive compensation of the eccentricity of the rotor suspension position of the bearingless motor. The observation quantity is easy to obtain and can be realized by designing a simple low-pass filtering link, and can better reflect the eccentricity of the rotor suspension position. The algorithm is simple to implement and the system structure is simple. The implementation steps of the scheme are as follows:

[0031] Step S1: First, actively apply the initial vector of eccentricity compensation

[0032] Step S2: Calculate the eccentricity compensation vector at the current moment

[0033] Step S3: Obtain the bearingless motor suspension current vector at the current moment And complete the suspension closed-loop control;

[0034] Step S4: The obtained bearingless motor suspension current vector Perform mathematical processing to obtain the anti-disturbance suspension current amplitude of the bearingless motor at the current moment and anti-eccentric suspension current amplitude

[0035] Step S5: Obtain the current bearingless motor tracking transformation matrix P t (k) and tracking step matrix dP xy (k);

[0036] Step S6: Repeat steps S2 to S5 to obtain the rotor eccentricity compensation vector in real time It is applied to the bearingless motor system to compensate for the eccentricity of the rotor suspension position until the rotor can run stably at the optimal point (stator geometric center).

[0037] The initial vector for eccentricity compensation in step S1 The setting is not unique and can be set in any direction according to actual needs.

[0038] The eccentricity compensation vector at the current moment in step S2 The calculation method is the tracking step matrix dP obtained at the last moment xy (k-1) and the unit vector The corresponding formula can be written as

[0039] Bearingless motor suspension current vector in step S3 The acquisition can be obtained by, but is not limited to, sampling the current sensor.

[0040] In step S3, the bearingless motor suspension closed-loop control system can adopt, but is not limited to, a typical control structure of a displacement outer loop-current inner loop. The basic principle is to set the radial displacement vector of the bearingless motor to Its actual sampling value Make a difference and consider the eccentricity compensation vector The function of the bearingless motor is to send it to the displacement regulator to obtain the radial suspension force setting value. Then, the suspension current vector setting value is obtained through the bearingless motor decoupling model The actual sampling value of the suspension current vector The difference is sent to the current regulator to obtain the suspension command voltage vector Finally, the inverter switching signal S is obtained through the modulation link L To achieve suspension closed-loop control of bearingless motor.

[0041] The bearingless motor suspension current vector in step S4 can be divided into the anti-disturbance suspension current vector and anti-eccentric suspension current vector The former is used to generate the radial suspension force part to resist the external disturbance force, and the latter is used to generate the radial suspension force part to resist the eccentric magnetic pull. For the latter anti-eccentric suspension current vector, the more serious the eccentricity of the rotor suspension position, the greater the amplitude of the additional suspension current vector required to resist the eccentric magnetic pull, that is, the anti-eccentric suspension current vector amplitude is The larger the rotor suspension position is, the greater the magnitude of the anti-eccentric suspension current is. It's the smallest.

[0042] The anti-disturbance suspension current vector in step S4 and anti-eccentric suspension current vector For the former, since the rotor of the bearingless motor is affected by a series of unknown disturbance forces, even in a stable state, the amplitude of the anti-interference suspension current is is also changing; the difference is that for the latter, the amplitude of the anti-eccentric suspension current Theoretically, it is a constant value in a stable state, that is, adding a low-pass filter (LPF, Low Pass Filter) can realize the extraction of the anti-eccentric suspension current component at the current moment. The corresponding formula can be written as

[0043] In step S5, the current moment of the bearingless motor tracking step matrix dP xy (k) is determined by the quadrant of the rotating coordinate system where the anti-eccentric suspension vector difference between the current moment and the previous moment is located, where the tracking step matrix dP xy and tracking transformation matrix P t Both are 2×2 matrices.

[0044] In step S5, in order to prevent the bearingless motor from fluctuating at the optimal suspension position, the proposed compensation method tracks the minimum anti-eccentricity suspension current vector amplitude, and the eccentricity compensation vector The rotor fluctuates back and forth at the optimal point, causing the rotor to fluctuate even in a stable state. A counting threshold c is set. Th ;Each eccentricity compensation vector The fluctuations will be recorded in the fluctuation count value c. When the fluctuation count value c is greater than the counting threshold c Th When the proposed rotor suspension position eccentricity compensation method stops, that is, the bearingless motor tracking step matrix dP at the current moment xy (k) is 0.

[0045] In step S5, in order to ensure that the proposed suspension position eccentricity compensation method can be restarted normally when the rotor suspension position eccentricity problem occurs again, a compensation current threshold i is set. Th , the current amplitude of the anti-eccentric suspension current at the current moment Greater than the minimum value of the anti-eccentric suspension current amplitude during the algorithm operation , the proposed suspension position eccentricity compensation method will restart.

[0046] Figure 1 It is a flow chart of a bearingless motor radial displacement detection error compensation method, tracking step matrix dP xy and tracking transformation matrix P t They are the 2×2 tracking step matrix and tracking transformation matrix respectively:

[0047]

[0048] Among them, dP 11 、dP 12 、dP 21 、dP 22 , P t11, P t12 , P t21 , P t22 is the value of each cell in the matrix.

[0049] Figure 2 To track the selection of the transformation matrix, αOβ and dOq are the stationary coordinate system and the rotating coordinate system of the suspension control subsystem, respectively.

[0050] Combination Figure 1 and Figure 2 The following is a detailed description of the specific process of the bearingless motor radial displacement detection error compensation method of the present invention. First, at the beginning of the algorithm, the initial vector of the eccentricity compensation is set. Then the eccentricity compensation vector at the current moment is calculated. The calculation of the eccentricity compensation vector at the current moment is The calculation method is the tracking step matrix dP obtained at the last moment xy (k-1) and the unit vector The corresponding formula can be written as Next, obtain the bearingless motor suspension current vector at the current moment The suspension closed-loop control is then completed. Perform mathematical processing to obtain the anti-disturbance suspension current amplitude of the bearingless motor at the current moment and anti-eccentric suspension current amplitude The above bearingless motor suspension current vector Can be divided into anti-disturbance suspension current vector and anti-eccentric suspension current vector The former is used to generate the radial suspension force part to resist the external disturbance force, and the latter is used to generate the radial suspension force part to resist the eccentric magnetic pull. For the latter anti-eccentric suspension current vector, the more serious the eccentricity of the rotor suspension position, the greater the amplitude of the additional suspension current vector required to resist the eccentric magnetic pull, that is, the anti-eccentric suspension current vector amplitude is The larger the rotor suspension position is, the greater the magnitude of the anti-eccentric suspension current is. Based on this, for the anti-disturbance suspension current vector For bearingless motors, since the rotor is subject to a series of unknown disturbance forces, even in a stable state, the amplitude of the anti-interference suspension current is is also changing; the difference is that for the anti-eccentric suspension current vector For the anti-eccentric suspension current amplitude Theoretically, it is a constant value in a stable state, that is, adding a low-pass filter link can realize the extraction of the anti-eccentric suspension current component at the current moment. The corresponding formula can be written as Finally, obtain the current bearingless motor tracking transformation matrix P t (k) and tracking step matrix dP xy (k) is used as the basis for calculating the eccentricity compensation vector at the next moment.

[0051] In order to further simplify the proposed compensation method, let dP 12 =dP 21 =P t12 =P t21 =0,dP 11 =dP 12 =dP, where dP is the compensation step length. t11 and P t21 The value of is related to the quadrant in which the anti-eccentric suspension current vector difference is located in the rotating coordinate system. The specific relationship is as follows: Figure 2 As shown, Figure 2 As an example, the anti-eccentric suspension current vector difference is located in the second quadrant of the rotating coordinate system. t11 =1,P t21 =-1, that is, the tracking transformation matrix can be written as:

[0052]

[0053] The present invention provides a bearingless motor radial displacement detection error compensation method, which further provides a counting threshold and a compensation current threshold, wherein the counting threshold c Th The purpose of setting is to prevent the optimal point fluctuation phenomenon of the proposed invention, that is, when tracking the minimum anti-eccentricity suspension current vector amplitude, the eccentricity compensation vector fluctuates back and forth at the optimal point, causing the rotor to fluctuate even in a stable state. Although this is only a fluctuation in the compensation size, under high-speed operation conditions, the impact of the optimal point fluctuation phenomenon on the bearingless motor suspension performance cannot be ignored. In addition, the current compensation threshold i Th The purpose of setting is to restart the proposed compensation method when the eccentricity of the rotor suspension position appears again.

[0054] It is worth mentioning that the use of a bearingless motor radial displacement detection error compensation method of the present invention can simplify the design of the displacement regulator, and the integral link in the traditional PID-based displacement regulator is no longer required, and the problems of integral parameter selection and integral saturation can be avoided. A bearingless motor radial displacement detection error compensation method of the present invention can achieve full compensation of the eccentricity of the bearingless motor rotor suspension position without relying on any parameters, so that the rotor can be stably suspended at the optimal point (stator geometric center). The scheme has a simple structure and is easy to implement, and the proposed compensation method is universal and suitable for actual engineering mass production.

[0055] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0056] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for compensating radial displacement detection error of a bearingless motor, characterized in that: Aiming at the problem of eccentricity of the rotor suspension position of the bearingless motor caused by non-ideal factors such as process assembly error, inconsistent device characteristics and device temperature drift, the rotor eccentricity in the motor suspension state is adaptively compensated to achieve the optimal position of the rotor suspension. This method considers that the position of the rotor in the state of minimum anti-eccentricity suspension current is the geometric center of the stator, and takes the anti-eccentricity suspension current of the bearingless motor as the observation object to achieve adaptive compensation of the eccentricity of the rotor suspension position of the bearingless motor. The observation quantity is obtained by designing a low-pass filter link, and can reflect the eccentricity of the rotor suspension position. The implementation steps of the scheme are as follows: Step S1: First, actively apply the initial vector of eccentricity compensation Step S2: Calculate the eccentricity compensation vector at the current moment Step S3: Obtain the bearingless motor suspension current vector at the current moment And complete the suspension closed-loop control; Step S4: The obtained bearingless motor suspension current vector Perform mathematical processing to obtain the anti-disturbance suspension current amplitude of the bearingless motor at the current moment and anti-eccentric suspension current amplitude Step S5: Obtain the current bearingless motor tracking transformation matrix P t (k) and tracking step matrix dP xy (k); Step S6: Repeat steps S2 to S5 to obtain the rotor eccentricity compensation vector in real time It is applied to the bearingless motor system to compensate for the eccentricity of the rotor suspension position until the rotor can run stably at the optimal point.

2. A bearingless motor radial displacement detection error compensation method according to claim 1, characterized in that: In step S1, the initial vector of the eccentricity compensation Any direction can be set according to actual needs.

3. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: The eccentricity compensation vector at the current moment in step S2 The calculation method is the tracking step matrix dP obtained at the last moment xy (k-1) and the unit vector The corresponding formula is the accumulation of the product of 4. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: The bearingless motor suspension current vector in step S3 The acquisition is obtained by sampling the current sensor.

5. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: In step S3, the bearingless motor suspension closed-loop control system adopts a typical control structure of displacement outer loop-current inner loop. The basic principle is to set the radial displacement vector of the bearingless motor to Its actual sampling value Make a difference and consider the eccentricity compensation vector The function of the bearingless motor is to send it to the displacement regulator to obtain the radial suspension force setting value. Then, the suspension current vector setting value is obtained through the bearingless motor decoupling model The actual sampling value of the suspension current vector The difference is sent to the current regulator to obtain the suspension command voltage vector Finally, the inverter switching signal S is obtained through the modulation link L To achieve suspension closed-loop control of bearingless motor.

6. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: The bearingless motor suspension current vector in step S4 is divided into an anti-disturbance suspension current vector and anti-eccentric suspension current vector Anti-disturbance suspension current vector Used to generate radial suspension force to resist external disturbance force, anti-eccentric suspension current vector The radial suspension force part used to resist the eccentric magnetic pull; for the anti-eccentric suspension current vector, the more serious the eccentricity of the rotor suspension position, the greater the amplitude of the additional suspension current vector required to resist the eccentric magnetic pull, that is, the amplitude of the anti-eccentric suspension current vector The larger the rotor suspension position is, the greater the magnitude of the anti-eccentric suspension current is. Reach the minimum.

7. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: The anti-disturbance suspension current vector in step S4 and anti-eccentric suspension current vector For the anti-disturbance suspension current vector For the bearingless motor, since the rotor is affected by the disturbance force, the anti-interference suspension current amplitude is Also changing; for anti-eccentric suspension current vector For the anti-eccentric suspension current amplitude It is a constant value in the stable state. A low-pass filter (LPF) is added to extract the anti-eccentric suspension current component at the current moment. The corresponding formula is written as 8. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: In step S5, the bearingless motor tracking step length matrix dP at the current moment xy (k) is determined by the quadrant of the rotating coordinate system where the anti-eccentric suspension vector difference between the current moment and the previous moment is located, where the tracking step matrix dP xy and tracking transformation matrix P t Both are 2×2 matrices.

9. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: The step S5 method is set with a counting threshold c Th ;Each eccentricity compensation vector The fluctuations will be recorded in the fluctuation count value c. When the fluctuation count value c is greater than the counting threshold c Th When the rotor suspension position eccentricity compensation method stops, the bearingless motor tracking step matrix dP xy (k) is 0.

10. The method for compensating radial displacement detection error of a bearingless motor according to claim 1, characterized in that: In step S5, the method sets a compensation current threshold i Th , the current amplitude of the anti-eccentric suspension current at the current moment Greater than the minimum value of the anti-eccentric suspension current amplitude during the algorithm operation , the suspension position eccentricity compensation method will restart.

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