CN113009937A - Flow control system and control method for array type switch valve - Google Patents
Flow control system and control method for array type switch valve Download PDFInfo
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Abstract
The invention relates to a flow control system and a control method facing array type switch valves, wherein a three-position four-way reversing valve and two groups of parallel array type switch valves are adopted to control a cylinder, so that the complexity of respectively performing inflow-outflow control on a single cavity of a hydraulic cylinder in the prior art is reduced, and a control algorithm is simplified; by setting a flow switching threshold value, each group of parallel array switch valves carry out large-flow regulation through multi-valve composite control signals based on pulse code-pulse width-pulse frequency modulation combination, and single-valve composite control signals based on pulse width-pulse frequency modulation combination carry out fine flow deviation regulation and control on single switch valves; the size of the selected single switch valve control signal is further determined by an optimization function based on flow deviation, valve port differential pressure change and valve switching times; in addition, through a switch optimization distribution strategy, the switching times of each valve are distributed averagely, the fatigue wear of the digital valve control system caused by the continuous switching of the switching valves is reduced to the maximum extent, and the service life of the digital valve control system is further prolonged.
Description
Technical Field
The invention relates to the field of hydraulic control systems, in particular to a flow control system and a control method for an array type switching valve.
Background
The high-performance valve is an important component of most hydraulic servo systems, the servo proportional valve is used as a key control element of the electro-hydraulic servo system, and the servo proportional valve is widely applied to the field of electro-hydraulic servo control due to the excellent precision control performance, but has the defects of sensitivity to impurities, high power consumption, high cost and low reliability. Along with the combined development of a hydraulic technology and a computer technology, an electro-hydraulic digital control system is developed at the same time, and the digital hydraulic valve is considered to be a replacement scheme with certain competitiveness for a traditional proportional servo valve due to the characteristics of high efficiency, high economy and high reliability.
In a digital valve control system, the flow control characteristics of the switch valves determine the position and speed control performance of a cylinder, and it is common to use distributed flow control units to simulate the four-side control of a proportional valve, i.e. to simulate the unilateral opening control of a valve port of the proportional valve through the flow control of each group of flow control units, wherein the flow control units may be single switch valves or a plurality of parallel-connected distributed switch valves. However, the above-mentioned valve control system based on the flow control unit has a problem of more or less flow control, and because the single switch valve has a small control flow, it is difficult to be applied to the large flow control situation, so that the demand of large-scale flow regulation can be met only by increasing the number of valves and using the on-off of different valves, but for such digital valve control system, when controlling the cylinder, because the control resolution is low, there are problems of unsatisfactory tracking performance and poor low-speed controllability.
In order to meet the requirement of flow resolution ratio in tracking control, the current solution mainly controls one of the switching valves in each flow control unit by adopting a pulse width modulation signal, continuously switches the switching valve at high frequency by applying the high-frequency pulse width modulation signal to output corresponding micro flow, and outputs average flow corresponding to the duty ratio in an effective linear interval by adjusting the duty ratio of the pulse width modulation signal, so as to improve the output flow resolution ratio.
The existing patent is helpful to meet the requirements of the digital valve control system on flow control and output flow resolution, but still has some defects and limitations:
(1) the existing switch valve cylinder control system is difficult to simultaneously consider control precision, hardware cost and control algorithm cost. In the existing system, two paths of parallel switch valves are configured in one cavity of a hydraulic cylinder, one path is connected with a pump source, the other path is connected with an oil tank, and the other cavity is the same in principle.
(2) When the pulse width modulation signal is used for carrying out micro flow control on the switch valve, the problems of non-linearity of flow, narrow adjustable range of duty ratio and low working frequency exist, and the flow control resolution of the switch valve is limited. The switch valve under the control of the duty ratio of the pulse width modulation signal can only output the linearly regulated flow within a certain range, and because the delay time of the switch, the motion time of the switch and the working frequency influence the flow characteristics of the switch valve, the switch valve has a control dead zone, a saturation zone and a non-linear zone. The smaller the switching delay time is, the narrower the flow dead zone and saturation zone ranges of the switching valve are; the smaller the switch movement time is, the narrower the nonlinear area of the flow of the switch valve is; the higher the working frequency is, the narrower the linear region is, and the wider the nonlinear region is, the narrower the controllable range of the flow rate is. Based on the factors, the problem of response delay control or nonlinear error exists when the switching valve performs flow control, so that the deviation regulation of the switching valve on the flow is not ideal, and the tracking control performance of the cylinder is influenced finally.
(3) Because the switching valves are switched continuously, only part of the switching valves are involved in the work and the rest of the switching valves are not in work in the flow control process, so that the difference of the abrasion degree of each switching valve is large. That is, when a plurality of on-off valves participate in flow control, if the flow rate flowing into or out of the hydraulic cylinder is required to be increased or decreased, the traditional control method is to increase or decrease a new on-off valve to participate in the work based on the original on-off valve participating in the work, so that a part of the on-off valves are less likely to be used in the flow control process, the difference between the wear condition of each on-off valve core and the remaining service life is too large, and if the on-off valves cannot be detached and replaced in time, the performance of the valve control system is easily adversely affected for a long time.
Disclosure of Invention
In view of the above, the present invention provides an array-type switching valve-oriented flow control system and a control method thereof, wherein a three-position four-way reversing valve and two groups of parallel array-type switching valves are used to control a cylinder, and the configuration mode reduces the complexity of the original control of respectively performing inflow and outflow of a single cavity of a hydraulic cylinder and simplifies the control algorithm; by setting a flow switching threshold value, each group of parallel array switch valves carry out large-flow regulation through multi-valve composite control signals based on pulse code-pulse width-pulse frequency modulation combination, single-valve composite control signals based on pulse width-pulse frequency modulation combination carry out fine flow deviation regulation and control on single switch valves, and the problems of flow nonlinearity, narrow duty ratio adjustable range, low working frequency and the like during single-valve pulse width modulation are compensated and improved through the composite control method; the size of the selected single switch valve control signal is further determined by an optimization function based on flow deviation, valve port differential pressure change and valve switching times; in addition, through a switch optimization distribution strategy, the switching times of each valve are distributed averagely, the fatigue wear of the digital valve control system caused by the continuous switching of the switching valves is reduced to the maximum extent, and the service life of the digital valve control system is further prolonged.
In order to achieve the purpose, the invention adopts the following technical scheme:
a flow control system facing to an array type switch valve comprises a driver, a valve pulse signal control module, a switching unit, a control algorithm module, a signal processing module, a three-position four-way reversing valve, a switch valve combination 1, a switch valve combination 2, a flowmeter, a pressure sensor, a hydraulic cylinder and a displacement sensor; the port A of the three-position four-way reversing valve is connected with the switch valve combination 1, and the port B of the three-position four-way reversing valve is connected with the switch valve combination 2; the switch valve combination 1 and the switch valve combination 2 are also respectively connected with two cavities of the hydraulic cylinder; the flow meter and the pressure sensor are arranged on a connecting oil path of the two cavities of the hydraulic cylinder and are respectively used for detecting the flow and the pressure on the connecting oil path of the two cavities of the hydraulic cylinder; the displacement sensor is arranged on a piston rod of the hydraulic cylinder; the output ends of the flowmeter, the pressure sensor and the displacement sensor are connected with the input end of the signal processing module; the output end of the signal processing module is connected with the control algorithm module; the output end of the control algorithm module is connected with the input end of the switching unit; the output end of the switching unit is connected with the input end of the valve pulse signal control module; the output end of the valve pulse signal control module is connected with the input end of the driver; the output end of the driver is connected to the three-position four-way reversing valve and the electromagnets on the switch valves for controlling the valves to work.
Further, the switch valve combinations 1 and 2 are both composed of a plurality of switch valves connected in parallel.
Further, the valve pulse signal control module comprises a multi-valve control module and a single-valve control module.
Furthermore, the control signal of the multi-valve control module is formed by compounding a pulse code, a pulse width and a pulse frequency control signal and is used for simultaneously controlling a plurality of switch valves to regulate the large flow; the control signal of the single valve control module is a pulse signal compounded by pulse width and pulse frequency control signals and used for controlling a single switch valve to carry out deviation regulation and control of small flow; the full open flow areas of the switch valves are all set to be equal.
A flow control method facing an array type switch valve comprises the following steps:
s1: detecting real-time position information of a cylinder, performing noise reduction processing on the detection information through a signal processing module to obtain an accurate value, and comparing the detection information with target information;
s2: converting the difference value of the comparison tracking into a real-time difference value between the target flow and the actual flow, judging whether a flow switching threshold value is reached by a control algorithm module according to the difference value, selecting a multi-valve control signal or a single-valve control signal to drive a switch valve, if the difference value between the target flow and the actual flow is greater than the flow switching threshold value, selecting the multi-valve control module by the system according to the current difference value, and obtaining a switch combination close to the current target flow through a control algorithm;
s3: based on S2, the control module calculates the pulse code control signal to be output to control the opening of the corresponding number of switch valves according to the preselected valve switch combination, if the calculated output flow does not reach the required target flow, and on the basis, the control algorithm module further judges the information of flow deviation, valve port pressure difference and switch switching times, and calculates the pulse width-pulse frequency composite control signal to be output to drive one of the remaining unopened switch valves according to the information, and controls the switch valve of the high-frequency switch to continuously adjust the flow so as to further enable the actual flow to approach the target flow;
s4: based on the multi-valve control signal obtained in the step S3, the system performs optimal distribution of switching times, and outputs a multi-valve composite control signal to the switching valve according to the result of the optimal distribution, and at the moment, the multi-valve control cycle is ended;
s5: when the difference value between the target flow and the actual flow is smaller than the flow switching threshold value, the system switches the multi-valve control module generating the valve pulse signal into the single-valve control module, and closes the original switch valve for flow adjustment, and the flow is controlled by one switch valve in each group of switch valves;
s6: when only a single valve is used for carrying out deviation regulation and control of flow, the control algorithm module judges information of flow deviation, valve port pressure difference and switch switching times, and calculates a pulse width-pulse frequency composite control signal required to be output according to the information so as to drive the single switch valve;
s7: based on the single valve control signal obtained in the step S6, the system performs optimal distribution of switching times, and outputs a single valve composite control signal to the switching valve according to the result of the optimal distribution, and at the moment, the single valve control cycle is ended;
s8: and when the current flow control period is finished, the system waits for the arrival of the next flow control period and judges whether the flow deviation in the new period reaches the flow switching threshold value.
Further, the optimized distribution of the switching times is as follows: firstly, judging a current control mode, namely multi-valve control or single-valve control; selecting a corresponding switch distribution mode according to a control mode, if the current flow control period is multi-valve control, selecting a corresponding number of switch valves to control according to the flow required to be output in the current flow control period, recording the switch valves which finish switch switching, closing the switch valves which participate in the work in the previous period when the next flow control period comes, and simultaneously, sequentially opening the switch valves which are not opened in the previous period from the closed switch valves according to the control flow requirement of the next period, and repeating the steps until the flow control process of the multi-valve is finished; if the single-valve control is adopted, the switch valves outputting flow in each control period are switched in turn, namely, in the control period T, a specific duty ratio is given to the first switch valve
Operating frequency of
In the control period 2T, the second switching valve is given a specific duty ratio
Operating frequency of
And repeatedly and alternately switching and using the switch valves in the switch valve combination according to the new control signal until the flow control process of the single valve is finished.
Furthermore, the pulse width-pulse frequency composite control signal is a pulse width modulation signal applied in a linear region of the average flow output by the switch valve, and the output flow is regulated by controlling a duty ratio; when the adjusted duty ratio enables the switch valve to output the nonlinear average flow, the control signal is changed into a pulse frequency modulation signal, the power-off time of the switch valve is fixed, the power-on time of the switch valve is increased or reduced, the working frequency of the switch valve is changed, and the flow nonlinearity is improved until the duty ratio is adjusted to output the linear average flow.
Furthermore, when the control algorithm module applies pulse code control signals to the multiple valves, the switch combination preselected in each control period is a result obtained through calculation of the control algorithm; meanwhile, parameter information of the switch valve is preset in the control algorithm module before use, when the multi-valve control is carried out, the system calculates equivalent flow of different switch combinations flowing into or out of the cylinder according to real-time flow deviation and real-time pressure information fed back by a pressure sensor on an oil way and valve port flow formulas according to the pressure information and the preset parameter information of the switch valve, so that the equivalent flow is close to target flow under the multi-valve control; and applying pulse code control signals and pulse width-pulse frequency composite control signals to one of the rest unopened switching valves at the same time, so that the multi-valve can also perform continuous flow regulation in the interval of performing segmented large-flow control.
Further, when a pulse width-pulse frequency composite control signal is applied to the single valve, an optimization function is set, and the optimization function mainly comprises flow deviation, the switching times of the valve and respective balance factors; in addition, the selection of the flow deviation balancing factor needs to consider the parameters and the performance of the closed-loop controller based on position error feedback, and the selection of the valve switch switching frequency balancing factor is related to the change of the valve port pressure difference; in the flow deviation regulation and control process, if pressure fluctuation is frequent, in a flow control period, the single-valve control module determines whether to finely adjust the working frequency of the pulse signal for driving the switching valve according to the sensitivity degree of the valve switching times to the parameters of the optimization function result.
The purpose of setting an optimization function for controlling a single switching valve is to find a trade-off between flow control accuracy and valve switching cost, and the value of the optimization function should be as small as possible under a constraint condition, and the optimization function specifically comprises the following variables: flow deviation, number of valve switch toggles, and respective trade-off factors. The flow deviation balancing factor needs to be selected in consideration of parameters and performance of a closed-loop controller based on position error feedback, and the balancing factor of the valve switching times is selected to be related to the change of the valve port pressure difference. By the method, when the single valve performs micro flow control, the switching times of the single valve are improved while the cylinder control precision in a limited range is ensured, so that the switching times of the valve adapt to the change of the valve port pressure difference in a reasonable range.
Further, when the target flow is smaller than the flow switching threshold, the single controlled switch valve is switched and used in turn under the switch optimization allocation strategy, if the control signal duty ratio of the new switch valve can still work in the flow linear region after switching and the valve port pressure difference change still meets the requirement of the optimization function, the working frequency of the control signal given to the new switch valve is still consistent with the working frequency of the previous control period, otherwise, the working frequency of the control signal is readjusted.
Further, the setting of the flow rate switching threshold value depends on the value of the flow rate passing through when the single on-off valve is fully opened.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention simplifies the connection structure by arranging the three-position four-way reversing valve and configuring the single-way parallel switch valve in the single cavity of the hydraulic cylinder, further reduces the hardware cost and the control cost of the digital valve control system, and ensures that the flow control is simpler. The mode that a plurality of parallel switch valves are configured in a single cavity and a single path enables calculation of cross flow to be omitted when target flow calculation is carried out, and a control algorithm is simplified; meanwhile, the number of the switch valves needed in the digital valve control system is greatly reduced through a configuration mode of combining the three-position four-way reversing valve with a plurality of parallel switch valves, and the configuration mode has better robustness and control stability compared with a configuration mode of four-side control of an analog proportional valve;
2. the invention drives and controls the single switch valve by the composite control method combining pulse width modulation and pulse frequency modulation, so that the control effect is better when the single valve is used for flow control. The pulse width modulation-pulse frequency modulation composite digital control method is characterized in that a pulse width modulation signal is used in a linear region to change a duty ratio so as to linearly control output flow, a pulse frequency modulation signal is used in a nonlinear region, and the power-on time of a switch valve is changed by fixing the power-off time of the switch valve, so that the linear region of the flow of the switch valve is widened, the frequency response of the switch valve is improved, the linear adjustable flow of the switch valve is smaller, and the flow resolution of the switch valve after compensation improvement is higher than that of the original single pulse width modulation; meanwhile, when multi-valve flow control is carried out, the sudden change range of the flow is reduced, the continuity of the output flow is improved, and the control precision of the hydraulic cylinder is finally improved;
3. according to the invention, through a switch optimization distribution strategy, the switching times of each switch valve are reasonably distributed, the phenomenon of uneven wear of each switch valve caused by continuous switch switching is reduced, and the residual service life of each switch valve is prolonged. When the valve is controlled, the on-off valves used in the current flow control period are recorded, and in the next flow control period, according to the requirement of the current target flow, the new on-off valves are switched and used in turn by further using an on-off optimization distribution strategy, and the on-off times of each valve are averaged. Through the strategy, the valve cores of the switch valves are ensured to be consistent in abrasion condition while the flow is effectively controlled, the residual service life of the switch valves is prolonged, and the frequent replacement of the switch valves is reduced.
Drawings
FIG. 1 is a schematic diagram of a control system architecture in one embodiment of the present invention;
FIG. 2 is a schematic diagram of a switch optimization assignment method in an embodiment of the present invention;
FIG. 3 is a flow chart of a control method during a flow control period in one embodiment of the present invention;
FIG. 4 is a diagram showing the relationship between the equivalent flow rate and the number of opening/closing valves in continuous flow control according to an embodiment of the present invention;
in the figure: 1. a driver; 2. a single valve control module; 3. a multi-valve control module; 4. a switching unit; 5. a control algorithm module; 6. a signal processing module; 7. a three-position four-way reversing valve; 8-1, a switch valve A; 8-2, a switch valve B; 8-3, a switch valve C; 8-4, a switch valve D; 9-1, a flowmeter A; 9-2, a flowmeter B; 10-1, a pressure sensor A; 10-2, a pressure sensor B; 11. a hydraulic cylinder; 12. a displacement sensor; 13-1, a switch valve E; 13-2, a switch valve F; 13-3, a switch valve G; 13-4 and an on-off valve H.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
The invention provides a flow control system facing an array type switching valve, which comprises a driver 1, a single valve control module 2, a multi-valve control module 3, a switching unit 4, a control algorithm module 5, a signal processing module 6, a three-position four-way reversing valve 7, a switching valve A (8-1), a switching valve B (8-2), a switching valve C (8-3), a switching valve D (8-4), a flow meter A (9-1), a flow meter B (9-2), a pressure sensor A (10-1), a pressure sensor B (10-2), a hydraulic cylinder 11, a displacement sensor 12, a switching valve E (13-1), a switching valve F (13-2), a switching valve G (13-3) and a switching valve H (13-4); the switch valves (A-D) and the switch valves (E-H) are respectively formed in a parallel connection mode and are respectively arranged on two cavity connecting oil paths of the hydraulic cylinder.
Referring to fig. 1, in the present embodiment, the specific connection relationship of the flow control system is as follows:
the hydraulic system comprises: the port A of the three-position four-way reversing valve 7 is connected with four switch valves (A-D) in parallel, and the port B is connected with the other four switch valves (E-H) in parallel; the switch valves (A-D) form a switch valve combination 1, the switch valves (E-H) form a switch valve combination 2, the switch valve combinations 1 and 2 are respectively connected with two cavities of the hydraulic cylinder, and the connecting oil path also comprises a flow meter A, B (9-1, 9-2) and a pressure sensor A, B (10-1, 10-2) which are respectively used for detecting the flow and the pressure on the connecting oil path of the two cavities of the cylinder; a high-precision displacement sensor 12 is arranged on a piston rod of the hydraulic cylinder;
the electric control system part: the output ends of the flow meter A, B (9-1, 9-2), the pressure sensor A, B (10-1, 10-2) and the displacement sensor 12 are connected with the input end of the signal processing module 6, and the output ends are used for carrying out noise reduction processing on detected flow, pressure and displacement signals; the output end of the signal processing module 6 is connected with the control algorithm module 5; the output end of the control algorithm module 5 is connected with the input end of the switching unit 4; the output end of the switching unit 4 is connected with the input end of a valve pulse signal control module (a single valve control module 2 and a multi-valve control module 3); the output end of the valve pulse signal control module (the single valve control module 2 and the multi-valve control module 3) is connected with the input end of the driver 1; the output end of the driver 1 is connected to the three-position four-way reversing valve 7 and the electromagnets on the switch valves for controlling the valves to work.
Preferably, the control signal of the multi-valve control module is formed by compounding a pulse code-pulse width-pulse frequency control signal and is used for simultaneously controlling a plurality of switch valves to carry out large-flow regulation; the control signal of the single valve control module is a pulse signal formed by compounding a pulse width and a pulse frequency control signal and is used for controlling the single switch valve to carry out deviation regulation and control of small flow.
Preferably, the full open flow areas of the respective switching valves are set to be equal in size.
In this embodiment, the switching valve at the dashed box indicates that the valve is driven by a pulse width-pulse frequency composite control signal.
Fig. 2 schematically illustrates the principle of the switch optimization allocation strategy of the present invention.
In the present embodiment, the broken line box represents the on-off valve in the high frequency on-off state in the current flow control period, and the solid line box represents the on-off valve in the fully open state in the continuous energization condition in the current flow control period.
In this embodiment, the procedure for optimizing the allocation policy for the switch is as follows:
firstly, judging a current control mode, namely multi-valve control or single-valve control; selecting corresponding switch distribution mode according to the control mode, if the current flow control period is multi-valve control, selecting corresponding number of switch valves to control according to the output flow, recording the switch valves completing switch switching, and then controlling the switch valves according to the output flowWhen a flow control period comes, closing the switch valves which participate in the work in the previous period, and simultaneously, sequentially opening the switch valves which are not opened in the previous period from the closed switch valves according to the flow control requirement of the next period, and repeating the steps until the multi-valve flow control process is finished; if the single-valve control is adopted, the switch valves outputting flow in each control period are switched in turn, namely, in the control period T, a specific duty ratio is given to the first switch valve
Operating frequency of
In the control period 2T, the second switching valve is given a specific duty ratio
Operating frequency of
And repeatedly and alternately switching and using the switch valves in the switch valve combination according to the new control signal until the flow control process of the single valve is finished.
Referring to fig. 3, the present embodiment also provides a flow control method facing the array type switching valve,
the control flow in a flow control period is mainly as follows:
s1: detecting real-time position information of a cylinder; the signal processing module carries out noise reduction processing on the detection information to obtain an accurate value, and compares the detection information with target information;
s2: converting the difference value of the comparison tracking into a real-time difference value between the target flow and the actual flow, judging whether a flow switching threshold value is reached by a control algorithm module according to the difference value, selecting a multi-valve control signal or a single-valve control signal to drive a switch valve, if the difference value between the target flow and the actual flow is greater than the flow switching threshold value, selecting the multi-valve control module by the system according to the current difference value, and obtaining a switch combination close to the current target flow through a control algorithm;
s3: based on S2, the control module calculates the pulse code control signal to be output to control the opening of the corresponding number of switch valves according to the preselected valve switch combination, if the calculated output flow does not reach the required target flow, and on the basis, the control algorithm module further judges the information of flow deviation, valve port pressure difference and switch switching times, and calculates the pulse width-pulse frequency composite control signal to be output to drive one of the remaining unopened switch valves according to the information, and controls the switch valve of the high-frequency switch to continuously adjust the flow so as to further enable the actual flow to approach the target flow;
s4: based on the multi-valve control signal obtained in the step S3, the system performs optimal distribution of switching times, and outputs a multi-valve composite control signal to the switching valve according to the result of the optimal distribution, and at the moment, the multi-valve control cycle is ended;
s5: when the difference value between the target flow and the actual flow is smaller than the flow switching threshold value, the system switches the multi-valve control module generating the valve pulse signal into the single-valve control module, and closes the original switch valve for flow adjustment, so that one switch valve in each group of switch valves is used for fine flow control;
s6: when only a single valve is used for carrying out deviation regulation and control of flow, the control algorithm module judges information of flow deviation, valve port pressure difference and switch switching times, and calculates a pulse width-pulse frequency composite control signal required to be output according to the information so as to drive the single switch valve;
s7: based on the single valve control signal obtained in the step S6, the system performs optimal distribution of switching times, and outputs a single valve composite control signal to the switching valve according to the result of the optimal distribution, and at the moment, the single valve control cycle is ended;
s8: and when the current flow control period is finished, the system waits for the arrival of the next flow control period and judges whether the flow deviation in the new period reaches the flow switching threshold value.
Preferably, the flow switching threshold is set according to the value of the flow passing through the single switch valve when the single switch valve is fully opened.
Preferably, the pulse width-pulse frequency composite control signal is a pulse width modulation signal applied in a linear region of the average flow output by the switch valve, and the output flow is regulated by controlling a duty ratio; when the adjusted duty ratio enables the switch valve to output the nonlinear average flow, the control signal is changed into a pulse frequency modulation signal, the power-off time of the switch valve is fixed, the power-on time of the switch valve is increased or reduced, the working frequency of the switch valve is changed, and the flow nonlinearity is improved until the duty ratio is adjusted to output the linear average flow. By the control signal, a linear region of the single valve output average flow is widened, and a resolution threshold of flow output is improved.
Preferably, when the pulse code control signal is applied to the multiple valves, the switch combination pre-selected in each control period is a result obtained through calculation of a control algorithm, the control algorithm simultaneously balances and considers large flow deviation and the switching times of each valve, and the balance factor is determined according to the control requirement of the system; meanwhile, parameter information of the switch valve is preset in the control algorithm module before use, when the multi-valve control is carried out, the system calculates equivalent flow of different switch combinations flowing into or out of the cylinder according to real-time flow deviation and real-time pressure information fed back by a pressure sensor on an oil way and valve port flow formulas according to the pressure information and the preset parameter information of the switch valve, so that the equivalent flow is close to target flow under the multi-valve control; in order to further reduce the flow deviation in the multi-valve control, pulse code control signals are applied, and meanwhile pulse width-pulse frequency composite control signals are applied to one of the remaining unopened switching valves, so that the multi-valve can also perform continuous flow regulation in the interval of performing segmented large-flow control; and meanwhile, the optimal distribution of the switching times is selected according to the switching times of all the switching valves, so that the switching valves participating in the work in each flow control period can be switched and used in turn in sequence to average the wear condition of all the valves.
Preferably, the pulse width-pulse frequency composite control signal for the single switch valve is in a composite form of variable duty ratio and variable working frequency.
Furthermore, the variable working frequency form of the pulse width-pulse frequency composite control signal of the single switch valve is realized by fixing the power-off time of the switch valve and changing the power-on time of the switch valve.
Preferably, when the hydraulic cylinder is controlled, the control accuracy of the cylinder is determined by a closed-loop controller based on position error feedback, and the output quantity of the closed-loop controller is the variable power-on time of the switching valve.
Preferably, when a pulse width-pulse frequency composite control signal is applied to a single switch valve, a control algorithm based on an optimization function is set, wherein the optimization function comprises flow deviation and the switch switching times of the valve, which are required for achieving high-precision tracking control; and the selection of the flow deviation balancing factor needs to consider the parameters and the performance of the closed-loop controller based on position error feedback, the balancing factor for setting the valve opening and closing times is suitable for the change of the valve port pressure difference, and the change of the valve port pressure difference value is used for representing the pressure fluctuation of a single cavity of the hydraulic cylinder. In the flow deviation regulation process, if pressure fluctuation is frequent, the result of the optimization function becomes sensitive to the switching times of the valve in a flow control period, and in order to ensure that the optimization function can obtain a smaller value on the premise of simultaneously considering control precision and switching cost, the single-valve control module determines whether to finely adjust the working frequency of the pulse signal for driving the switch valve according to the sensitivity degree of the switching times of the valve to the parameters of the result of the optimization function.
It is further noted that the above optimization function for controlling a single switch valve is intended to find a trade-off between flow control accuracy and valve switching cost, and should be as small as possible under the constraint condition, and specifically includes the following variables: flow deviation, number of valve switch toggles, and respective trade-off factors. The selection of the flow deviation balancing factor needs to consider the parameters and the performance of the closed-loop controller based on the position error feedback, and the selection of the balancing factor of the switching times of the valve switch is related to the change of the valve port pressure difference. By the method, when the single valve performs micro flow control, the switching times of the single valve are improved while the cylinder control precision in a limited range is ensured, so that the switching times of the valve adapt to the change of the valve port pressure difference in a reasonable range.
Preferably, when the target flow is smaller than the flow switching threshold, the single controlled switch valve is switched and used in turn under the switch optimization allocation strategy, if the control signal duty ratio of the new switch valve can still work in the flow linear region after switching and the valve port pressure difference change still meets the requirement of the optimization function, the working frequency of the control signal given to the new switch valve is still consistent with the working frequency of the previous control period, otherwise, the working frequency of the control signal is readjusted.
Fig. 4 schematically shows the relationship between the equivalent through-flow rate and the number of opening/closing valves when continuous flow control is performed in the present invention.
In this embodiment, Q represents the flow rate that a single on-off valve can pass when fully open, the shade of the color represents the different on-off valves used, and the dotted line represents that there is currently one on-off valve that is controlled by the pulse width-pulse frequency composite control signal;
it can be seen that when continuously increasing flow is output, the steps are as follows: firstly, driving a first switch valve by a single-valve composite control signal to enable the output linearized average flow to be from zero to the flow Q when the first switch valve is fully opened; at the moment, the first switching valve is controlled to be kept fully opened; and then, continuously controlling the second switch valve to be in a high-frequency switch state, so that the output linearized average flow of the second switch valve is from zero to the flow Q when the second switch valve is fully opened, controlling the first switch valve and the second switch valve to be fully opened at the moment, and repeating the steps until all the switch valves are opened.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (10)
1. A flow control system facing to an array type switch valve is characterized by comprising a driver, a valve pulse signal control module, a switching unit, a control algorithm module, a signal processing module, a three-position four-way reversing valve, a switch valve combination 1, a switch valve combination 2, a flowmeter, a pressure sensor, a hydraulic cylinder and a displacement sensor; the port A of the three-position four-way reversing valve is connected with the switch valve combination 1, and the port B of the three-position four-way reversing valve is connected with the switch valve combination 2; the switch valve combination 1 and the switch valve combination 2 are also respectively connected with two cavities of the hydraulic cylinder; the flow meter and the pressure sensor are arranged on a connecting oil path of the two cavities of the hydraulic cylinder and are respectively used for detecting the flow and the pressure on the connecting oil path of the two cavities of the hydraulic cylinder; the displacement sensor is arranged on a piston rod of the hydraulic cylinder; the output ends of the flowmeter, the pressure sensor and the displacement sensor are connected with the input end of the signal processing module; the output end of the signal processing module is connected with the control algorithm module; the output end of the control algorithm module is connected with the input end of the switching unit; the output end of the switching unit is connected with the input end of the valve pulse signal control module; the output end of the valve pulse signal control module is connected with the input end of the driver; the output end of the driver is connected to the three-position four-way reversing valve and the electromagnets on the switch valves for controlling the valves to work.
2. The array-type switching valve-oriented flow control system according to claim 1, wherein the switching valve assemblies 1 and 2 are each composed of a plurality of switching valves connected in parallel.
3. The array-style switch valve-oriented flow control system of claim 1, wherein the valve pulse signal control module comprises a multi-valve control module and a single-valve control module.
4. The array-type switching valve-oriented flow control system according to claim 3, wherein the control signals of the multi-valve control module are formed by compounding pulse code-pulse width-pulse frequency control signals and are used for controlling the plurality of switching valves to adjust the large flow rate; the control signal of the single valve control module is a pulse signal compounded by pulse width and pulse frequency control signals and used for controlling a single switch valve to carry out deviation regulation and control of small flow; the full open flow areas of the switch valves are all set to be equal.
5. A flow control method facing an array type switch valve is characterized by comprising the following steps:
s1: detecting real-time position information of a cylinder, performing noise reduction processing on the detection information through a signal processing module to obtain an accurate value, and comparing the detection information with target information;
s2: converting the difference value of the comparison tracking into a real-time difference value between the target flow and the actual flow, judging whether a flow switching threshold value is reached by a control algorithm module according to the difference value, selecting a multi-valve control signal or a single-valve control signal to drive a switch valve, if the difference value between the target flow and the actual flow is greater than the flow switching threshold value, selecting the multi-valve control module by the system according to the current difference value, and obtaining a switch combination close to the current target flow through a control algorithm;
s3: based on S2, the control module calculates the pulse code control signal to be output to control the opening of the corresponding number of switch valves according to the preselected valve switch combination, if the calculated output flow does not reach the required target flow, and on the basis, the control algorithm module further judges the information of flow deviation, valve port pressure difference and switch switching times, and calculates the pulse width-pulse frequency composite control signal to be output to drive one of the remaining unopened switch valves according to the information, and controls the switch valve of the high-frequency switch to continuously adjust the flow so as to further enable the actual flow to approach the target flow;
s4: based on the multi-valve control signal obtained in the step S3, the system performs optimal distribution of switching times, and outputs a multi-valve composite control signal to the switching valve according to the result of the optimal distribution, and at the moment, the multi-valve control cycle is ended;
s5: when the difference value between the target flow and the actual flow is smaller than the flow switching threshold value, the system switches the multi-valve control module generating the valve pulse signal into the single-valve control module, and closes the original switch valve for flow adjustment, and the flow is controlled by one switch valve in each group of switch valves;
s6: when only a single valve is used for carrying out deviation regulation and control of flow, the control algorithm module judges information of flow deviation, valve port pressure difference and switch switching times, and calculates a pulse width-pulse frequency composite control signal required to be output according to the information so as to drive the single switch valve;
s7: based on the single valve control signal obtained in the step S6, the system performs optimal distribution of switching times, and outputs a single valve composite control signal to the switching valve according to the result of the optimal distribution, and at the moment, the single valve control cycle is ended;
s8: and when the current flow control period is finished, the system waits for the arrival of the next flow control period and judges whether the flow deviation in the new period reaches the flow switching threshold value.
6. The flow control method for array-type switching valves according to claim 5, wherein the optimized distribution of the switching times is as follows: firstly, judging a current control mode, namely multi-valve control or single-valve control; selecting a corresponding switch distribution mode according to a control mode, if the current flow control period is multi-valve control, selecting a corresponding number of switch valves to control according to the flow required to be output in the current flow control period, recording the switch valves which finish switch switching, closing the switch valves which participate in the work in the previous period when the next flow control period comes, and simultaneously, sequentially opening the switch valves which are not opened in the previous period from the closed switch valves according to the control flow requirement of the next period, and repeating the steps until the flow control process of the multi-valve is finished; if the single-valve control is adopted, the switch valves outputting flow in each control period are switched in turn, namely, in the control period T, a specific duty ratio is given to the first switch valve
Operating frequency of
In the control period 2T, the second switching valve is given a specific duty ratio
Operating frequency of
And repeatedly and alternately switching and using the switch valves in the switch valve combination according to the new control signal until the flow control process of the single valve is finished.
7. The flow control method facing the array type switching valve as claimed in claim 5, wherein the pulse width-pulse frequency composite control signal is a pulse width modulation signal applied in a linear region of the average flow output from the switching valve, and the output flow is adjusted by controlling a duty ratio; when the adjusted duty ratio enables the switch valve to output the nonlinear average flow, the control signal is changed into a pulse frequency modulation signal, the power-off time of the switch valve is fixed, the power-on time of the switch valve is increased or reduced, the working frequency of the switch valve is changed, and the flow nonlinearity is improved until the duty ratio is adjusted to output the linear average flow.
8. The array-type switch valve-oriented flow control method of claim 5, wherein the control algorithm module pre-selects the switch combination in each control period when the pulse code control signal is applied to the multi-valve, and the switch combination is calculated by the control algorithm; meanwhile, parameter information of the switch valve is preset in the control algorithm module before use, when the multi-valve control is carried out, the system calculates equivalent flow of different switch combinations flowing into or out of the cylinder according to real-time flow deviation and real-time pressure information fed back by a pressure sensor on an oil way and valve port flow formulas according to the pressure information and the preset parameter information of the switch valve, so that the equivalent flow is close to target flow under the multi-valve control; and applying pulse code control signals and pulse width-pulse frequency composite control signals to one of the rest unopened switching valves at the same time, so that the multi-valve can also perform continuous flow regulation in the interval of performing segmented large-flow control.
9. The flow control method for array-type switching valves according to claim 5, wherein when the pulse width-pulse frequency composite control signal is applied to a single valve, an optimization function is set, the optimization function mainly comprises flow deviation, the switching times of the valve and respective trade-off factors; setting a trade-off factor of the switching times of the valve switch to be related to the change of the differential pressure of the valve port; in the flow deviation regulation and control process, if pressure fluctuation is frequent, in a flow control period, the single-valve control module determines whether to finely adjust the working frequency of the pulse signal for driving the switching valve according to the sensitivity degree of the valve switching times to the parameters of the optimization function result.
10. The flow control method for array-type switching valves according to claims 5 and 6, wherein when the target flow is smaller than the flow switching threshold, the single switching valve is alternately switched for use under the switching optimization allocation strategy, if the duty ratio of the control signal of the new switching valve can still work in the flow linear region after switching and the change of the valve port pressure difference still meets the requirement of the optimization function, the operating frequency of the control signal of the new switching valve is still consistent with the operating frequency of the previous control cycle, otherwise, the operating frequency of the control signal is readjusted.
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