CN111324127A - Control method based on frequency converter and control device for walking positioning equipment - Google Patents
Control method based on frequency converter and control device for walking positioning equipment Download PDFInfo
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Abstract
The invention relates to a control method based on a frequency converter, which is used for carrying out high-precision positioning on walking positioning equipment and comprises the following steps: determining the minimum forward frequency and the minimum reverse frequency of a frequency converter corresponding to the minimum forward speed and the minimum reverse speed of the walking positioning equipment; determining the corresponding specific speeds when the walking positioning equipment respectively outputs specific frequencies in the forward direction and the reverse direction; inputting a step frequency signal and recording a frequency-speed response curve; and according to the recorded frequency-speed response curve, setting an adaptive PID parameter for the frequency converter by adopting a Ziegler-Nichols step response method. The invention also relates to a control device for a walking positioning apparatus, comprising: a motor driven by the frequency converter; a position sensor; and the control unit controls the output frequency of the frequency converter based on the control method, so that the motor is controlled to realize high-precision positioning of the walking positioning equipment.
Description
Technical Field
The invention relates to a control method based on a frequency converter, which is used for carrying out high-precision positioning on walking positioning equipment. The invention also relates to a control device for the walking positioning equipment.
Background
The traditional positioning control method generally uses a proximity switch for control or is suitable for high-speed and low-speed control. The method is suitable for occasions with relaxed requirements on precision and positioning time. However, the above control method is not suitable for application scenarios requiring high precision or time-optimal control positioning.
The positioning control system calculates the current required target speed in real time for the walking positioning equipment to output the corresponding frequency of the frequency converter by establishing a mathematical model of a slope generator of the frequency converter. However, the actual speed of the walking positioning device has a certain deviation from the target speed, and needs to be corrected by using PID control. Because the mathematical model and the field working condition of each on-site walking positioning device are different, a lot of time is spent on trying to obtain PID parameters through experience on the field, and the optimal effect cannot be achieved.
It would therefore be desirable to provide a method of adapting PID parameters that greatly reduces the burden on engineers in debugging without having to understand the mathematical model of the position control system and that also results from adaptation are superior to traditional empirical tuning.
Disclosure of Invention
In order to solve the technical problems, the invention provides a high-precision positioning control method based on frequency converter control, which provides some necessary basic control parameters for frequency converter control and can also adapt to PID parameters.
According to one aspect of the invention, a frequency converter-based control method is provided, which is used for positioning walking positioning equipment with high precision, and comprises the following steps: determining the minimum forward frequency and the minimum reverse frequency of a frequency converter corresponding to the minimum forward speed and the minimum reverse speed of the walking positioning equipment; determining the corresponding specific speeds when the walking positioning equipment respectively outputs specific frequencies in the forward direction and the reverse direction; inputting a step frequency signal and recording a frequency-speed response curve; and setting an adaptive PID parameter for the frequency converter by adopting a Ziegler-Nichols step response method according to the recorded frequency-speed response curve.
The step of determining the minimum forward frequency and the minimum reverse frequency of the frequency converter corresponding to the minimum forward speed and the minimum reverse speed of the walking positioning equipment comprises the following steps:
starting from 0 Hz, increasing the frequency of a frequency converter in a certain frequency step length in each cycle period, judging that the walking positioning equipment does forward motion once the walking positioning equipment has a forward real-time speed, and taking the real-time output frequency of the frequency converter as the minimum forward frequency corresponding to the minimum forward speed, otherwise, judging that the system is abnormal when the walking positioning equipment has a reverse real-time speed, and stopping the walking positioning equipment;
starting from 0 Hz, reducing the frequency of the frequency converter in a certain frequency step length in each cycle period, judging that the walking positioning equipment does reverse motion once the walking positioning equipment has reverse real-time speed, and taking the real-time output frequency of the frequency converter as the minimum reverse frequency corresponding to the minimum reverse speed, otherwise, judging that the system is abnormal when the walking positioning equipment has the forward real-time speed, and stopping the walking positioning equipment.
In the step of determining the specific speed corresponding to the walking positioning equipment when the frequency converter outputs the specific frequency, a plurality of equal parts of the maximum frequency of the frequency converter are taken as frequency step length, and the multiple of the frequency step length between the minimum forward frequency or the minimum reverse frequency of the frequency converter and the maximum frequency of the frequency converter is taken as the specific frequency.
The step of determining the corresponding specific speed of the walking positioning equipment when the frequency converter outputs the specific frequency comprises the following steps: firstly, driving a walking positioning device to a safe track position with typical working conditions and long enough distance, then slowly outputting frequency to the specific frequency by the walking positioning device, recording the time and the position of the walking positioning device at the moment when the actual output frequency is equal to the specific frequency, keeping the specific frequency until the actual position of the walking positioning device exceeds a preset safe stop position, stopping the running of the walking positioning device and recording the time and the position at the moment, thereby calculating the speed corresponding to the specific frequency according to the change of the time and the position; and repeating the processes for a plurality of times for each specific frequency, and calculating the average speed corresponding to the specific frequency according to the speed corresponding to the specific frequency calculated by each process to be used as the specific speed corresponding to the walking positioning equipment when the frequency converter outputs the specific frequency. The above-mentioned predetermined safety stop position is determined empirically, requiring that at any possible frequency of the frequency converter the walking positioning device has passed a sufficiently long sampling time and is already in uniform motion before reaching this safety stop position.
The step of inputting a step frequency signal and recording a frequency-velocity response curve comprises: repeatedly driving the walking positioning equipment to a safe track position with typical working conditions and a long enough distance, then setting the output frequency of the frequency converter to be a preset first frequency, switching the output frequency of the frequency converter from the first frequency to a preset second frequency different from the first frequency until the walking positioning equipment runs at a first speed corresponding to the first frequency at a constant speed again, recording the time of frequency switching as a zero moment, recording the speed of the walking positioning equipment at the end of each cycle period in a plurality of continuous cycle periods in the process of stepping from the first speed to the second speed and the time offset value relative to the zero moment, wherein the first frequency and the second frequency are both at the minimum forward frequency or the minimum reverse frequency of the frequency converter and the maximum forward frequency of the frequency converter Taking values between frequencies; calculating the speed average value corresponding to the cycle period of the sequence according to the recorded speed at the end of the cycle period of the same sequence in the repeated times; and calculating the average value of the time deviation value relative to the zero time corresponding to the cycle period of the sequence according to the time deviation value relative to the zero time when the cycle period of the same sequence in the recorded repeated times is ended.
Preferably, the speed sampling values corresponding to the time offset value average values are obtained by performing smoothing filtering on the speed average values corresponding to the time offset value average values, and the speed sampling values and the corresponding time offset value average values form a speed sampling value array. Although it is considered that the speed average value obtained in the above description is directly used as the speed sample value to form the speed sample value array without performing smoothing filtering processing on the speed average value corresponding to each time offset value average value, a speed sample value-time offset value average value curve obtained at this time may not be smooth.
In one embodiment of the frequency converter-based control method according to the present invention, in order to more accurately represent the measurement results and reduce the influence of random errors, smoothing and filtering processing is required for the acquired speed data, such as a moving average method, in which m adjacent data are continuously and gradually averaged along the full length of N data to obtain a direct arithmetic average, and the formula is as follows:
wherein p and q are positive integers smaller than m, and m is p + q +1, wiIs a weighting coefficient, and
ykcorresponding to the variable to be smoothed, here the speed average/speed sample value for which the average of the respective time offset value corresponds. The processing may be performed using a moving average method.
The selection of parameters m, p, q for sliding smoothing directly affects the smoothing effect on the data. If m is larger, the locally averaged adjacent data is more, and although the smoothing effect is larger, the random error of frequent random fluctuation is favorably inhibited, the deterministic components of high-frequency change can be averaged together and weakened; on the contrary, if m is smaller, the low frequency random fluctuation may be reduced without averaging, i.e. it is not beneficial to suppress random errors, therefore, the parameter values should be reasonably selected according to the purpose of smoothing and the actual variation of data.
More specifically, a front-end point smoothing method may be adopted, and the expression is:
or a back-end point smoothing method, the expression is:
preferably, the parameters m, p, q selected by the smoothing filtering process satisfy the following relationship:
15＞p＞10，15＞q＞10，31＞m＞21。
more preferably, the parameters m, p, and q selected by the smoothing filtering process have the following values:
p＝10，
q is 12, and
m＝25。
in a further embodiment of the frequency converter-based control method according to the invention, the smoothing filter process may also use a first-order lag filter method in addition to the moving average method. The moving average method may be modified to replace the clipped average filtering method or the weighted recursive average filtering method.
Firstly, determining a first point and a second point on a speed sampling value-time deviation value average value curve formed by speed sampling values and time deviation value average values in the speed sampling value array, so that the slope of a straight line passing through the first point and the second point is the same as the inflection point tangent of the speed sampling value-time deviation value average value curve; and then, in a coordinate system of the average value of the speed sampling value and the time deviation value, calculating straight lines where the first point and the second point are located by using a straight line formula.
In one variant embodiment, for a speed sample value array consisting of speed sample values and corresponding time offset value averages, a first point is first determined in the speed sample value array, which first point is a point in the speed sample value array in the direction of increasing time offset value averages at which the following conditions are simultaneously satisfied: the speed sampling values of the point and the four points behind the point are all larger than the sum of the minimum speed sampling value and 0.4 times of the difference between the maximum speed sampling value and the minimum speed sampling value; determining a second point in the array of speed samples, the second point being a point along the direction of increasing average of the time offset value at which the following condition is satisfied at the same time at the last of the array of speed samples: the speed sampling values of the point and the four points before the point are all smaller than the difference obtained by subtracting 0.4 times of the difference between the maximum speed sampling value and the minimum speed sampling value from the maximum speed sampling value; and then, in a coordinate system of the speed sampling value-time deviation value average value, calculating straight lines where the first point and the second point are located by using a straight line formula.
In one embodiment of the frequency converter-based control method according to the invention, a third point is determined in the speed sample value array, which third point is the point in the speed sample value array along the direction of increasing time offset at which the following conditions are simultaneously satisfied for the first one: the speed sampling values of the point and the four points before the point are all less than the sum of the minimum speed sampling value and 0.12 times of the difference between the maximum speed sampling value and the minimum speed sampling value; then, the time offset value corresponding to the third point is recorded as the first time offset value.
The time offset corresponding to the first speed may be calculated from the obtained straight line, and the calculated time offset may be referred to as a first time offset value. That is, a time offset value corresponding to the first speed is found on the straight line where the first point and the second point are found.
In the step of setting the adaptive PID parameters for the frequency converter by adopting a Ziegler-Nichols step response method: recording the first time offset value as τ; recording the ratio of the difference between the second speed and the first speed to the corresponding difference between the second frequency and the first frequency as K; calculating a time offset corresponding to the second speed according to the obtained straight line, recording the time offset as a second time offset value, and obtaining a difference between the second time offset value and the first time offset value, and recording the difference as T; then, an adaptive PID control parameter K is calculated according to the following Ziegler-Nichols parameter table of the slow speed performancep，TI，TD：
According to another aspect of the present invention, there is also provided a control apparatus for a walking positioning device, the control apparatus comprising: the motor is driven by the frequency converter and is used for driving the walking positioning equipment; a position sensor that detects a real-time position of the walking positioning device at a certain cycle period; the control unit calculates the real-time speed according to the detected change of the real-time position of the walking positioning equipment in the cycle period; the control unit controls the output frequency of the frequency converter based on the frequency converter-based control method, so that the motor is controlled to realize high-precision positioning of the walking positioning equipment.
Through the design, the problem of high-precision positioning on the motion track of the equipment is solved regardless of external factors such as mechanical performance, track shape, walking path and the like of the equipment. Therefore, the invention can be widely applied to the rapid high-precision positioning control occasions in the logistics industry, the steel industry, the food industry and other industries. In practical use, the positioning precision can reach +/-2 mm by matching with a proper PID parameter.
Drawings
Fig. 1 shows a flow chart of a frequency converter based control method according to the invention;
FIG. 2 shows K, τ, and T in a mathematical model of a typical step response.
Detailed Description
Fig. 1 shows a control device for a walking positioning device according to the invention. The control device includes: the motor is driven by the frequency converter and is used for driving the walking positioning equipment; a position sensor that detects a real-time position of the walking positioning device at a certain cycle period; and the control unit calculates the real-time speed according to the detected change of the real-time position of the walking positioning equipment in the cycle period, wherein the control unit controls the output frequency of the frequency converter based on the control method based on the frequency converter, so that the motor is controlled to realize high-precision positioning of the walking positioning equipment.
According to one aspect of the invention, a frequency converter-based control method is provided, which is used for positioning walking positioning equipment with high precision, and comprises the following steps: determining the minimum forward frequency and the minimum reverse frequency of a frequency converter corresponding to the minimum forward speed and the minimum reverse speed of the walking positioning equipment; determining the corresponding specific speeds when the walking positioning equipment respectively outputs specific frequencies in the forward direction and the reverse direction; inputting a step frequency signal and recording a frequency-speed response curve; and setting an adaptive PID parameter for the frequency converter by adopting a Ziegler-Nichols step response method according to the recorded frequency-speed response curve.
The step of determining the minimum forward frequency and the minimum reverse frequency of the frequency converter corresponding to the minimum forward speed and the minimum reverse speed of the walking positioning equipment comprises the following steps:
starting from 0 Hz, increasing the frequency of a frequency converter in a certain frequency step length in each cycle period, judging that the walking positioning equipment does forward motion once the walking positioning equipment has a forward real-time speed, and taking the real-time output frequency of the frequency converter as the minimum forward frequency corresponding to the minimum forward speed, otherwise, judging that the system is abnormal when the walking positioning equipment has a reverse real-time speed, and stopping the walking positioning equipment;
starting from 0 Hz, reducing the frequency of the frequency converter in a certain frequency step length in each cycle period, judging that the walking positioning equipment does reverse motion once the walking positioning equipment has reverse real-time speed, and taking the real-time output frequency of the frequency converter as the minimum reverse frequency corresponding to the minimum reverse speed, otherwise, judging that the system is abnormal when the walking positioning equipment has the forward real-time speed, and stopping the walking positioning equipment.
In the step of determining the specific speed corresponding to the walking positioning equipment when the frequency converter outputs the specific frequency, a plurality of equal parts of the maximum frequency of the frequency converter are taken as frequency step length, and the multiple of the frequency step length between the minimum forward frequency or the minimum reverse frequency of the frequency converter and the maximum frequency of the frequency converter is taken as the specific frequency.
The control unit calculates to obtain the current required target speed of the walking positioning equipment through a mathematical model, and corresponds to the output frequency according to the linear proportion according to the minimum frequency and the specific speed corresponding to the specific frequency. In order to make the ratio as linear as possible, it is desirable to acquire as many velocity values at a particular frequency as possible.
Therefore, the walking positioning equipment is obtained through calculation and respectively output in the positive direction and the negative direction
(100>n4>1, typically 10) is used. In this embodiment, the actual average speed is measured for a series of equally divided frequency values between the maximum frequency and the minimum frequency of the frequency converter.
The walking positioning device is first driven to a safe track position with typical operating conditions and a sufficiently long distance. Slowly accelerating the walking positioning equipment from the stopped working condition to
When the actual output frequency is equal to
Then, the time Start _ Times and the actual position Start _ POSmm are recorded. Keeping the output frequency until the actual position is larger than the preset SStopmm, immediately outputting a stop command. And records the time value End _ Times and the actual position End _ POSmm at the time of outputting the stop command.
It is particularly noted that in the algorithm for speed, the value of End _ POS should be taken instead of using SStopThe numerical value of (c).
The average velocities in this process are:
the above process was repeated (n4 \u)1-1)(100>n4_1>1, typically 10) times and recording all relevant data
Averaging the obtained values to obtain the forward frequency
At run time, actual average speed
Comprises the following steps:
similarly, the walking location device is calculated at various frequency values
The corresponding actual average speed.
Similarly, the corresponding actual average speed of the walking positioning device under each frequency value when the walking positioning device moves in the opposite direction is calculated. In actual operation, the operation condition of the walking positioning equipment should be paid attention to in real time, and the equipment is stopped in time when abnormal conditions are found.
Next, a step frequency signal is input, and a response curve of the velocity is recorded. The walking positioning device is driven to a safe track position with typical working conditions and a long enough distance. The frequency converter for controlling the walking positioning equipment outputs a first frequency x5_1Hz(fmax>x5_1>0,). When the actual output frequency is equal to x5_1In Hz, after the walking positioning equipment runs at a constant speed for a period of time, the output frequency is directly changed into a second frequency x5_2Hz(fmax>x5_2>0,) the actual speed of the walking pointing device will quickly reach a steady state with the step change in frequency. The moment of switching the frequency is taken as zero moment, and n from the beginning of the frequency step signal to the constant-speed operation again is recorded5_1Real-time speed V _ Curve [1] of one cycle]_1.V，V_Curve[2]_ 1.V，…，V_Curve[n5_1]_1V and time offset from zero V _ Curve [1]]_1.Time，V_Curve[2]_ 1.Time，…，V_Curve[n5_1]_1Time, where V _ Curve [1]]_1.Time＝0。
Repeating the above process (n)5_2For n) times of5_2The arithmetic mean is performed on the data generated in each repetition step to obtain the average speed at the end of the first cycle period, namely:
the second to nth can be obtained by the same algorithm5_2Average value of speed at the end of a cycle V _ Curve [2 ]].V，…，
Similarly, the first to n-th5_2Average value of time deviation values at the end of each cycle V _ Curve [1]].Time，V_Curve[2].Time，…，V_Curve[n5_1]Time. Wherein V _ Curve [1]].Time＝0。
In order to more accurately represent the measurement results and reduce the influence of random errors, smoothing and filtering processing needs to be carried out on the acquired speed data, and a moving average method can be adopted for processing. That is, along the full length of N data, continuously sliding one by one, and taking m adjacent data as direct arithmetic mean.
The general expression is:
wherein p and q are any positive integer less than m, and m is p + q + 1. w is aiIs a weighting coefficient, and
the expression of the front-end point smoothing method is:
the expression of the back-end point smoothing method is:
in this embodiment, let n5_1200, p 12, q 12, using equal weight endpoint smoothing (i.e., equal weight endpoint smoothing)
) Then, the data obtained after filtering is:
V_Filter[1]＝V_Curve[1].V
…
…
…
…
V_Filter[200]＝V_Curve[200].V
thus, a velocity response curve for a frequency step process is determined, wherein the velocity is an equal weight endpoint smoothed value of a plurality of measured values. Namely, the speed sampling values corresponding to the time deviation value average values are obtained by performing smooth filtering processing on the speed average values corresponding to the time deviation value average values, and the speed sampling values and the corresponding time deviation value average values form a speed sampling value array.
Since the step response curve of the walking position device is obtained in the above method steps, as shown in fig. 2, the classical Ziegler-Nichols step response method can be used to adapt the PID parameters, since the Ziegler-Nichols step response method does not require the establishment of a mathematical model of the controlled object but only relies on the parameter adaptation method of the device step response curve. Therefore, under the open-loop, loaded and stable state of the system, a step signal u (t) is given to the system, the step response y (t) is obtained, and the relevant dynamic response data is recorded. K, tau and T are then calculated from the dynamic data by tangent methods, two-point methods or by means of a set of collected dynamic response data, which are well known in the art, and the values of K, tau and T are obtained by means of manual drawing or by means of observation or calculation using third-party tool software such as MATLAB.
According to the classical control theory, the control object can be approximately represented by a first-order inertia plus pure delay link, and the transfer function is as follows:
where K is the amplification factor (unitless), T is the time constant (units are s), and τ is the delay time (units are s).
We will use the filtered speed data and time offset values for further processing by using the step response of the Ziegler-Nichols algorithm.
FIG. 2 shows K, τ, and T in a mathematical model of a typical step response. It should be understood that the incremental step approach is used herein, i.e., the second frequency is greater than the first frequency; if a decreasing step is used, the algorithm works the same.
As an engineering control unit, the practical characteristics of a control object and the practical reliability and convenience of an algorithm need to be considered, and on the basis of a Ziegler-Nichols algorithm, the following algorithms are designed to calculate K, tau and T.
Calculating the amplification factor K
The method comprises the following steps:
that is, the ratio of the difference between the second speed and the first speed (smoothed speed sample value) to the corresponding difference between the second frequency and the first frequency is denoted as K.
Calculating the sum of the time constant T and the delay time tau (T + tau)
The following algorithm is used:
finding a first point in the array of speed samples that simultaneously satisfies the following requirements:
V_Filter[i1]≥V_Filter[1]+0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i1+1]≥V_Filter[1]+0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i1+2]≥V_Filter[1]+0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i1+3]≥V_Filter[1]+0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i1+4]≥V_Filter[1]+0.4×(V_Filter[n5_1]-V_Filter[1])
and records the value V _ Filter [ i ] at this point1]And a time offset value V _ Curve [ i ]1].Time。
That is, a first point is determined in the speed sample value array, which is a point along the direction of increasing time offset value average value at which the following condition is satisfied simultaneously at a first one of the speed sample value arrays: the speed sampling values of the point and the four subsequent points are all larger than the sum of the minimum speed sampling value and 0.4 times of the difference between the maximum speed sampling value and the minimum speed sampling value.
Finding the last point in the speed sampling value array which can simultaneously meet the following requirements:
V_Filter[n5_1-i2]≤V_Filter[n5_1]-0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[n5_1-i2-1]
≤V_Filter[n5_1]-0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[n5_1-i2-2]≤V_Filter[n5_1]-0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[n5_1-i2-3]≤V_Filter[n5_1]-0.4×(V_Filter[n5_1]-V_Filter[1])
V_Filter[n5_1-i2-4]≤V_Filter[n5_1]-0.4×(V_Filter[n5_1]-V_Filter[1])
and records the value V _ Filter [ n ] at this point5_1-i2]And time offset value
That is, a second point is determined in the speed sample value array, which is a point where the following condition is satisfied simultaneously at the last one in the speed sample value array along the direction in which the average value of the time offset value increases: the speed sampling values of the point and the four points before the point are all smaller than the difference obtained by subtracting 0.4 times of the difference between the maximum speed sampling value and the minimum speed sampling value from the maximum speed sampling value.
The two 0.4 times involved in the above calculation were used to empirically approximate the knee tangent of the velocity sample value-time offset value mean curve. In practice, therefore, a point slightly offset by a factor of 0.4 may be selected, as long as the effect of better approximating the knee tangent of the average curve of the velocity sample value versus the time offset value is achieved. Furthermore, when the first point and the second point are determined on the speed sample value-time offset value average value curve formed by the speed sample values and the time offset value average value in the speed sample value array, in practice, only a straight line passing through the first point and the second point needs to be found in any way, and the slope of the straight line is the same as the inflection point tangent of the speed sample value-time offset value average value curve.
And then, in a speed sampling value-time deviation value average value coordinate system, calculating straight lines where the first point and the second point are located by using a straight line formula.
By the linear formula, we can know that through the first point (
V_Filter[i1]) And a second point (
V_Filter[n5_1-i2]) The equation of the straight line of (1) is:
from fig. 2, it can be seen that the value of (T + τ) is equal to y — V _ Filter [ n ] on the above straight line5_1]At the intersection of (a) and (b). Namely:
calculating the value of tau
In order to determine the value of the delay time τ, the control unit finds the last point in the array of speed samples that simultaneously satisfies the following requirements:
V_Filter[i3]≤V_Filter[1]+0.12×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i3-1]≤V_Filter[1]+0.12×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i3-2]≤V_Filter[1]+0.12×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i3-3]≤V_Filter[1]+0.12×(V_Filter[n5_1]-V_Filter[1])
V_Filter[i3-4]≤V_Filter[1]+0.12×(V_Filter[n5_1]-V_Filter[1])
note down V _ Filter [ i ]3]Corresponding V _ Curve [ i ]3].Time。
The tau value is calculated by the following method:
τ＝V_Curve[i3].Time
τ is in units of s.
It should be noted that the above algorithm is actually the point along the direction of increasing time offset at which the first in the array of speed sample values can simultaneously satisfy the following condition: the speed sampling value of the point and the four points before the point is less than the sum of the minimum speed sampling value and 0.12 times of the difference between the maximum speed sampling value and the minimum speed sampling value. The value of 0.12 times τ is empirically determined, and the reason for selecting this point while considering the first four points is to avoid the fluctuation of the individual points from affecting the calculation result. Thus, in practice, a point slightly offset by a factor of 0.12 may also be selected, and more or less than four points before it may also be considered simultaneously.
In another embodiment of the present invention, after a linear equation of the first point and the second point is obtained in the process of calculating the T value, the time offset value at the first speed may be directly solved, that is, the intersection point of the linear equation and the x-axis (y ═ V _ Filter [1]) in fig. 2 may be obtained.
Using the value of (T + τ) already found above, after τ is found, the value of T can be found as:
t is in units of s.
After obtaining the values of K, τ and T, K can be calculated from the following Low-speed Performance Ziegler-Nichols parameter Table, taking into account the fact that the frequency converter-based control method according to the invention requires that the walking positioning device have a small overshootp，TI，TD。
TABLE 1 Ziegler-Nichols parameter Table
The results are as follows:
can calculate K according to actual working conditionp，TI，TDThe values of (c) are further fine-tuned to optimize the adjustment. Can store Kp，TI，TDFor use in frequency converter control. Through the adaptive algorithm, the PID parameters can be adapted, the debugging burden of an engineer is greatly reduced, and the adaptive result is superior to the traditional experience adjustment.
The foregoing describes preferred embodiments of the present invention, but the spirit and scope of the present invention is not limited to the specific disclosure herein. Those skilled in the art can freely combine and expand the above-described embodiments in accordance with the teachings of the present invention to make further embodiments and applications within the spirit and scope of the present invention. The spirit and scope of the present invention are not to be limited by the specific embodiments but by the appended claims.
Claims (20)
1. A control method based on a frequency converter is used for carrying out high-precision positioning on walking positioning equipment and comprises the following steps:
determining the minimum forward frequency and the minimum reverse frequency of a frequency converter corresponding to the minimum forward speed and the minimum reverse speed of the walking positioning equipment;
determining the corresponding specific speeds when the walking positioning equipment respectively outputs specific frequencies in the forward direction and the reverse direction;
inputting a step frequency signal and recording a frequency-speed response curve;
and setting an adaptive PID parameter for the frequency converter by adopting a Ziegler-Nichols step response method according to the recorded frequency-speed response curve.
2. The transducer-based control method of claim 1, wherein the step of determining a transducer minimum forward frequency and a minimum reverse frequency corresponding to a minimum forward speed and a minimum reverse speed of the walking position device comprises:
starting from 0 Hz, increasing the frequency of a frequency converter in a certain frequency step length in each cycle period, judging that the walking positioning equipment does forward motion once the walking positioning equipment has a forward real-time speed, and taking the real-time output frequency of the frequency converter as the minimum forward frequency corresponding to the minimum forward speed, otherwise, judging that the system is abnormal when the walking positioning equipment has a reverse real-time speed, and stopping the walking positioning equipment;
starting from 0 Hz, reducing the frequency of the frequency converter in a certain frequency step length in each cycle period, judging that the walking positioning equipment does reverse motion once the walking positioning equipment has reverse real-time speed, and taking the real-time output frequency of the frequency converter as the minimum reverse frequency corresponding to the minimum reverse speed, otherwise, judging that the system is abnormal when the walking positioning equipment has the forward real-time speed, and stopping the walking positioning equipment.
3. The transducer-based control method according to claim 2, wherein in the step of determining the specific speed corresponding to the walking position device when the transducer outputs the specific frequency, the specific frequency is determined as a multiple of a frequency step between a minimum forward frequency or a minimum reverse frequency of the transducer and a maximum frequency of the transducer, with a number of equal parts of the maximum frequency of the transducer as the frequency step.
4. The frequency converter-based control method according to claim 1, wherein the step of determining a specific speed corresponding to the walking positioning device when the frequency converter outputs a specific frequency comprises:
firstly, driving a walking positioning device to a safe track position with typical working conditions and long enough distance, then slowly outputting frequency to the specific frequency by the walking positioning device, recording the time and the position of the walking positioning device at the moment when the actual output frequency is equal to the specific frequency, keeping the specific frequency until the actual position of the walking positioning device exceeds a preset safe stop position, stopping the running of the walking positioning device and recording the time and the position at the moment, thereby calculating the speed corresponding to the specific frequency according to the change of the time and the position;
and repeating the processes for a plurality of times for each specific frequency, and calculating the average speed corresponding to the specific frequency according to the speed corresponding to the specific frequency calculated by each process to be used as the specific speed corresponding to the walking positioning equipment when the frequency converter outputs the specific frequency.
5. The frequency converter based control method of claim 1, wherein the step of inputting the step frequency signal and recording the frequency-velocity response curve comprises:
repeatedly driving the walking positioning equipment to a safe track position with typical working conditions and a long enough distance, then setting the output frequency of the frequency converter to be a preset first frequency, switching the output frequency of the frequency converter from the first frequency to a preset second frequency different from the first frequency until the walking positioning equipment runs at a first speed corresponding to the first frequency at a constant speed again, recording the time of frequency switching as a zero moment, recording the speed of the walking positioning equipment at the end of each cycle period in a plurality of continuous cycle periods in the process of stepping from the first speed to the second speed and the time offset value relative to the zero moment, wherein the first frequency and the second frequency are both at the minimum forward frequency or the minimum reverse frequency of the frequency converter and the maximum forward frequency of the frequency converter Taking values between frequencies;
calculating the speed average value corresponding to the cycle period of the sequence according to the recorded speed at the end of the cycle period of the same sequence in the repeated times;
and calculating the average value of the time deviation value relative to the zero time corresponding to the cycle period of the sequence according to the time deviation value relative to the zero time when the cycle period of the same sequence in the recorded repeated times is ended.
6. The frequency converter-based control method according to claim 5, wherein the speed sample values corresponding to the time offset value average values are obtained by performing a smoothing filtering process on the speed average values corresponding to the time offset value average values, and the speed sample values and the corresponding time offset value average values form a speed sample value array.
7. The frequency converter-based control method according to claim 6, wherein the smoothing filtering process uses a moving average method as follows:
wherein p and q are positive integers smaller than m, and m is p + q +1, wiIs a weighting coefficient, and
8. the frequency converter-based control method according to claim 7, wherein the moving average method adopted by the smoothing filtering process is a front-end point smoothing method, and the expression is as follows:
9. the frequency converter-based control method according to claim 7, wherein the moving average method adopted by the smoothing filtering process is a back-end point smoothing method, and the expression is as follows:
10. the frequency converter-based control method according to claim 7, wherein the parameters m, p, and q selected by the smoothing filtering process satisfy the following relationship:
15＞p＞10，15＞q＞10，31＞m＞21。
11. the frequency converter-based control method according to claim 10, wherein the parameters m, p, q selected by the smoothing filtering process satisfy
p＝10，
q is 12, and
m＝25。
12. the frequency converter-based control method according to claim 6, wherein the smoothing filtering process employs a first-order lag filtering method.
13. The frequency converter-based control method according to claim 6, wherein the smoothing filtering process employs a limiting average filtering method or a weighted recursive average filtering method.
14. The frequency converter based control method according to claim 6,
determining a first point and a second point on a speed sampling value-time deviation value average value curve formed by speed sampling values and time deviation value average values in the speed sampling value array, so that the slope of a straight line passing through the first point and the second point is the same as the inflection point tangent of the speed sampling value-time deviation value average value curve;
and in a speed sampling value-time deviation value average value coordinate system, calculating straight lines where the first point and the second point are located by using a straight line formula.
15. The frequency converter based control method according to claim 6,
determining a first point in the array of speed samples along the direction of increasing average of the time offset value at which a first one of the array of speed samples satisfies the following condition: the speed sampling values of the point and the four points behind the point are all larger than the sum of the minimum speed sampling value and 0.4 times of the difference between the maximum speed sampling value and the minimum speed sampling value;
determining a second point in the array of speed samples, the second point being a point along the direction of increasing average of the time offset value at which the following condition is satisfied at the same time at the last of the array of speed samples: the speed sampling values of the point and the four points before the point are all smaller than the difference obtained by subtracting 0.4 times of the difference between the maximum speed sampling value and the minimum speed sampling value from the maximum speed sampling value;
and in a speed sampling value-time deviation value average value coordinate system, calculating straight lines where the first point and the second point are located by using a straight line formula.
16. Frequency converter based control method according to claim 14 or 15,
determining a third point in said array of velocity samples, the third point being a point along the direction of increasing average of the time offset value at which the following condition is satisfied simultaneously at the first of the array of velocity samples: the speed sampling values of the point and the four points before the point are all less than the sum of the minimum speed sampling value and 0.12 times of the difference between the maximum speed sampling value and the minimum speed sampling value; then the
And recording the time offset value corresponding to the third point as a first time offset value.
17. Frequency converter based control method according to claim 14 or 15,
and calculating the time offset corresponding to the first speed according to the obtained straight line, and recording the time offset as a first time offset value.
18. The frequency converter-based control method according to claim 16, wherein in the step of setting adaptive PID parameters for the frequency converter using a Ziegler-Nichols step response method:
recording the first time offset value as τ;
recording the ratio of the difference between the second speed and the first speed to the corresponding difference between the second frequency and the first frequency as K;
calculating a time offset corresponding to the second speed according to the obtained straight line, recording the time offset as a second time offset value, and obtaining a difference between the second time offset value and the first time offset value, and recording the difference as T;
then, an adaptive PID control parameter K is calculated according to the following Ziegler-Nichols parameter table of the slow speed performancep，TI，TD：
19. The frequency converter-based control method according to claim 17, wherein in the step of setting adaptive PID parameters for the frequency converter using a Ziegler-Nichols step response method:
recording the first time offset value as τ;
recording the ratio of the difference between the second speed and the first speed to the corresponding difference between the second frequency and the first frequency as K;
calculating a time offset corresponding to the second speed according to the obtained straight line, recording the time offset as a second time offset value, and obtaining a difference between the second time offset value and the first time offset value, and recording the difference as T;
then, an adaptive PID control parameter K is calculated according to the following Ziegler-Nichols parameter table of the slow speed performancep，TI，TD：
20. A control device for a walking positioning apparatus, the control device comprising:
the motor is driven by the frequency converter and is used for driving the walking positioning equipment;
a position sensor that detects a real-time position of the walking positioning device at a certain cycle period;
a control unit for calculating the real-time speed according to the detected change of the real-time position of the walking positioning equipment in the cycle period
Wherein the control unit controls the output frequency of the frequency converter based on the frequency converter-based control method according to any one of claims 1 to 17, thereby controlling the motor to realize high-precision positioning of the walking positioning device.
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