CN109212967B - Online tracking smooth switching method for control mode of hydraulic material tester - Google Patents
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- 238000006073 displacement reaction Methods 0.000 claims abstract description 9
- 101100190464 Caenorhabditis elegans pid-2 gene Proteins 0.000 claims description 6
- 101100190462 Caenorhabditis elegans pid-1 gene Proteins 0.000 claims description 4
- 239000010720 hydraulic oil Substances 0.000 claims description 4
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention discloses an online tracking smooth switching method of a control mode of a hydraulic material tester, which carries out closed-loop learning on an input signal of a mode to be switched according to errors of driving voltages of two control modes before and after switching, so that a driving signal for switching an actual driving system is kept unchanged at the switching moment, and the impact of displacement, load or strain cannot occur in the closed-loop forming process of the control mode after switching. The method can be used universally in a material testing machine, can realize smooth switching between any two control channels, cannot damage a test piece in the switching process, and meets the requirements of various test standards.
Description
Technical Field
The invention relates to the field of control of hydraulic material testing machines, in particular to an online tracking method for controlling smooth switching of modes.
Background
The material testing machine is an instrument for testing physical and mechanical properties of various materials (such as metal, nonmetal, composite materials and the like), mechanical parts, engineering structures and the like under different conditions. In order to meet the test requirements of various different test standards and various materials, the control software of the material testing machine needs to have greater flexibility, and for the control mode, displacement, load and strain control modes are generally needed. In the test process, flexible combination test is often required to be carried out among various control modes, and smooth switching must be ensured in the switching process of various control modes according to the requirements of international universal test standards, namely, load impact cannot be generated in the switching process.
The existing control strategy is mainly to make the difference between the system error under the current closed-loop control and the system error under the control mode to be switched approximately zero by adjusting the input signal of the control closed-loop. This method is only suitable for handover with static state. The transfer function and controller parameters of the system are different for different control modes, and therefore, it is difficult to achieve a completely smooth switching.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an online tracking smooth switching method of a control mode of a hydraulic material tester, which carries out closed-loop learning on an input signal of a to-be-switched mode according to the error of driving voltage of two control modes before and after switching, so that the driving signal for switching an actual driving system is kept unchanged at the switching moment, and the impact of displacement, load or strain cannot occur in the closed-loop forming process of the control mode after switching.
The invention adopts the following technical scheme:
the on-line tracking smooth switching method of the control mode of the hydraulic material testing machine is characterized in that each channel of the hydraulic material testing machine adopts a PID control mode; acquiring a learning signal according to the error of the driving voltage of the two control modes before and after switching; the learning signal of the mode to be switched is learned in a closed loop mode through the PI tracker, so that the driving voltage after switching can track the driving voltage before switching in real time, therefore, the driving signal of an actual driving system is kept unchanged at the switching moment, and the impact of displacement, load or strain cannot occur in the closed loop forming process of the control mode after switching.
The general procedure for switching from control channel 1 to control channel 2 is as follows:
when the control mode is in channel 1, a closed loop of channel 1 is formed, and the driving voltage of the PID-1 controller controlling channel 1 is calculated in the following manner:
in the formula, P1Is the proportionality coefficient of channel 1, I1Is the integral coefficient of channel 1, D1Is the differential coefficient of channel 1. e.g. of the type1(t) is the difference of the command signal and the output feedback signal for channel 1.
Controlling the drive voltage u of channel 11And (t) outputting the hydraulic oil to the servo valve to drive the valve core of the servo valve to move, so that the hydraulic oil flows into the oil cylinder to actuate the oil cylinder.
Meanwhile, the PID-2 controller of the control channel 2 is also in a working state, and the PI tracker is adopted to learn the input command signal of the control channel 2, so that the driving voltage u of the control channel 22(t) ability to track u in real time1(t) of (d). Learning process tracingThe method comprises the following steps:
learn1-2(t)＝Pe3(t)+I∫e3(t)dt
in the formula, lern1-2(t) is the input command signal for channel 2 for learning; p is the proportionality coefficient of the PI tracker and I is the integral coefficient of the PI tracker. P2Is the proportionality coefficient of channel 2, I2Is the integral coefficient of channel 2, D2Is the differential coefficient of channel 2. e.g. of the type3(t) is the driving voltage u of channel 11(t) and the driving voltage u of channel 22(t) difference. e.g. of the type2(t) is the difference between the input command signal and the output feedback signal for channel 2, i.e. lern1-2(t) difference from the feedback signal of channel 2.
When receiving an interrupt message of a switching command, the drive voltage of the servo valve is switched from the channel 1 to the channel 2, and at the same time, a command input signal of the channel 2 is learned from the switching process by the signal learn1-2(t) command input signal to switch to channel 2.
Further, the control channel of the material testing machine comprises displacement, load and strain. And the PID control and PI tracker of each channel are realized by adopting an analog circuit or a digital controller. Switching the drive voltage of the servo valve from channel 1 to channel 2 is achieved by an analog switch, relay control or digital controller programming.
The invention has the beneficial effects that: the invention provides an online tracking smooth switching method of a control mode of a hydraulic material tester, which is characterized in that input signals of a mode to be switched are subjected to closed-loop learning according to errors of driving voltages of two control modes before and after switching, so that driving signals of an actual driving system are switched to be kept unchanged at the switching moment, and the impact of displacement, load or strain cannot occur in the closed-loop forming process of the control mode after switching. The method can be used universally in a material testing machine, can realize smooth switching between any two control channels, cannot damage a test piece in the switching process, and meets the requirements of various test standards.
Drawings
Fig. 1 shows a general inter-control-mode switching process.
Fig. 2 is a schematic diagram of smooth switching of control modes.
Detailed Description
The control method of the material testing machine adopts PID control, the system characteristics of displacement, load and strain control modes are different, and the PID parameters of each control mode are different. Without loss of generality, the smooth switching process between control modes is described by any two control modes, and fig. 1 shows a common switching process from a control channel 1 to a control channel 2.
In the figure, the control mode is in a 1-channel closed loop state, r1 is an input command signal of 1 channel, y1 is an output signal of 1 channel and serves as a feedback signal to an input terminal, e1 is an error signal of channel 1, the value of the error signal is the difference value between r1 and y1, and u1 is an output signal of the error signal e1 after passing through a PID-1 controller and is a driving voltage of the control channel 1.
In the formula, P1Is the proportionality coefficient of channel 1, I1Is the integral coefficient of channel 1, D1Is the differential coefficient of channel 1. e.g. of the type1(t) is the difference of the command signal and the output feedback signal for channel 1.
The control signal u1 actuates movement of the servo valve spool to cause closed loop operation of the hydraulic system. The switch sw1 being in the channel 1 position indicates that the system is now in a 1-channel closed loop control state. r2 is the input command signal for channel 2 to be switched, e2 is the error for control channel 2, u2 is the drive voltage for control channel 2, and y2 is the output feedback signal for control channel 2.
When switch sw1 is in channel 1, PID-1 closed loop control causes drive voltage u1 to be at a steady state value. If the process of smooth switching is not performed, the initial driving voltage u2 is different from the driving voltage u1 at the moment before switching, when switching from channel 1 to channel 2. Since y2 is the channel 2 output signal in the closed loop of the channel 1 control mode and its value is related to the input command r1, the error signal e2 is also different from e 1. The driving voltage u2 will inevitably generate jitter during the process of forming the closed loop of the channel 2 immediately after switching, thereby causing the output signal of the controlled system to generate sudden change. This abrupt change makes the switching process unsmooth and may have an effect on the test piece.
The conventional method is to smoothly switch the channel 2 by controlling the input command signal r2 during switching, and the common method is to make the error signal e2 of the channel to be switched equal to the error e1 in the current control mode by changing r 2. This method controls the error signal not to generate jitter, but cannot ensure that the initial voltage of the driving voltage u2 of channel 2 is the same as before switching. Generally, the initial voltage of the integration element should be set to zero before use. And when the driving voltage u1 of channel 1 is not zero, the initial driving voltage u2 of channel 2 is not equal to u 1. Therefore, the switching process inevitably generates a certain jitter.
The invention adopts the input instruction signal of the channel to be switched based on the online learning of the closed loop PI tracker shown in figure 2 to ensure that the driving voltages of the two channels are equal. At the same time of the control channel 1, the PID-2 controller of the control channel 2 is also in a working state, and the PI tracker is adopted to learn the input command signal of the control channel 2, so that the driving voltage u of the control channel 22(t) ability to track u in real time1(t) of (d). The main principle is as follows: the difference e3 between the driving voltages u1 and u2 is converted into a learn1-2 signal through a PI tracker, and then the learn1-2 signal is input into a channel 2 to be used as an input command.
The learning process is described as:
learn1-2(t)＝Pe3(t)+I∫e3(t)dt
in the formula, lern1-2(t) input command signal of channel 2 for learning, P is proportional coefficient of PI tracker, I is integral coefficient of PI tracker. P2Is a Chinese character' tongProportionality coefficient of track 2, I2Is the integral coefficient of channel 2, D2Is the differential coefficient of channel 2. e.g. of the type3(t) is the driving voltage u of channel 11(t) and the driving voltage u of channel 22(t) difference. e.g. of the type2(t) is the difference between the input command signal and the output feedback signal for channel 2, i.e. lern1-2(t) difference from the feedback signal of channel 2. At this time, the PI tracker, PID-2, u1 constitute a closed loop tracking system. When u2 and u1 have difference, the PI tracker calculates corresponding lern 1-2 input PID-2 according to the difference e 3. Since the integration element can eliminate the steady-state error, the result of tracking is u 2-u 1.
When receiving the interrupt message of the switching instruction, the switch sw1 and the switch sw2 are switched simultaneously. The switch sw1 switches the drive voltage of the servo valve from channel 1 to channel 2, and the switch sw2 switches the command input signal of channel 2 from the switching process learning signal learn1-2(t) command input signal to switch to channel 2.
The method changes the command signal of the channel 2 in real time to learn through the PI controller tracking function so that the driving voltages u2 and u1 are equal. At the switching moment, the switches sw1 and sw2 are switched simultaneously, the channel 2 is suddenly switched to a new command signal of the channel 2 by a spare 1-2 signal, and the process ensures that the voltage signal u2 input to the servo valve is kept unchanged at the moment when the system is switched to the channel 2 under the condition of not changing PID-2 parameters, so that the whole process in the process of forming a new closed loop of the channel 2 is continuously controllable and does not generate sudden change.
As described above, the method for controlling the mode smooth switching of the material testing machine according to the present invention is described by taking the switching from the channel 1 to the channel 2 as an example. In fact, switching between any two channels is similar. In any control mode closed loop state, the PI trackers of the other control modes learn the spare 1-2 signal online to wait for switching, and when receiving the switching interrupt message, the switches sw1 and sw2 are immediately switched to the new control mode at the same time, and the new closed loop control is immediately formed. Because the tracker is learned online, the method is suitable for smooth switching at any moment, and switching can be performed without reaching a steady state.
Claims (4)
1. The on-line tracking smooth switching method of the control mode of the hydraulic material testing machine is characterized in that each channel of the hydraulic material testing machine adopts a PID control mode; acquiring a learning signal according to the error of the driving voltage of the two control modes before and after switching; the learning signal of the mode to be switched is learned in a closed loop mode through the PI tracker to serve as an input instruction, so that the driving voltage after switching can track the driving voltage before switching in real time, the driving signal of an actual driving system is kept unchanged at the switching moment, and the impact of displacement, load or strain cannot occur in the closed loop forming process of the control mode after switching.
2. The method of claim 1, wherein the general procedure for switching from control channel 1 to control channel 2 is as follows:
when the control mode is in channel 1, a closed loop of channel 1 is formed, and the driving voltage of the PID-1 controller controlling channel 1 is calculated in the following manner:
in the formula, P1Is the proportionality coefficient of channel 1, I1Is the integral coefficient of channel 1, D1Is the differential coefficient of channel 1; e.g. of the type1(t) is the difference of the command signal and the output feedback signal for channel 1;
controlling the drive voltage u of channel 11(t) outputting the hydraulic oil to a servo valve to drive a valve core of the servo valve to move, so that the hydraulic oil flows into the oil cylinder to actuate the oil cylinder;
meanwhile, the PID-2 controller of the control channel 2 is also in a working state, and the PI tracker is adopted to learn the input command signal of the control channel 2, so that the driving voltage u of the control channel 22(t) ability to track u in real time1(t); the learning process is described as:
learn1-2(t)＝Pe3(t)+I∫e3(t)dt
in the formula, lern1-2(t) is the input command signal for channel 2 for learning; p is a proportional coefficient of the PI tracker, I is an integral coefficient of the PI tracker; p2Is the proportionality coefficient of channel 2, I2Is the integral coefficient of channel 2, D2Is the differential coefficient of channel 2; e.g. of the type3(t) is the driving voltage u of channel 11(t) and the driving voltage u of channel 22(t) difference; e.g. of the type2(t) is the difference between the input command signal and the output feedback signal for channel 2, i.e. lern1-2(t) difference from the feedback signal of channel 2;
when receiving an interrupt message of a switching command, the drive voltage of the servo valve is switched from the channel 1 to the channel 2, and at the same time, a command input signal of the channel 2 is learned from the switching process by the signal learn1-2(t) command input signal to switch to channel 2.
3. The method of claim 1, wherein the PID control and PI tracker of each channel are implemented with analog circuits or with digital controllers; switching the drive voltage of the servo valve from channel 1 to channel 2 is achieved by an analog switch, relay control or digital controller programming.
4. The method of claim 1, wherein the control channel of the material testing machine comprises displacement, load, strain.
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| EP0897110A2 (en) * | 1997-08-13 | 1999-02-17 | Japan Tobacco Inc. | Material testing machine |
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| CA2575690C (en) * | 2004-08-04 | 2009-07-14 | Fisher Controls International Llc | System and method for transfer of feedback control for a process control device |
| CN2758748Y (en) * | 2004-12-15 | 2006-02-15 | 中国科学院金属研究所 | Heater for heat machinery fatigue tester |
| CN101101247A (en) * | 2007-01-25 | 2008-01-09 | 北京交通大学 | Digital type self-adaptive electro-hydraulic fatigue test machine and realization method |
| CN102114517B (en) * | 2010-11-30 | 2012-11-07 | 浙江大学 | Displacement-force compound control lifting system for forging manipulator |
| CN105003479B (en) * | 2015-07-10 | 2017-06-16 | 华中科技大学 | A kind of big flow plug-in 3-position 4-way electrohydraulic servo valve and its control method |
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| CN107947675B (en) * | 2017-12-28 | 2023-01-31 | 中国科学院宁波材料技术与工程研究所 | Device for smoothly switching switched reluctance control modes |
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| EP0897110A2 (en) * | 1997-08-13 | 1999-02-17 | Japan Tobacco Inc. | Material testing machine |
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| 基于前馈跟踪补偿的电液复合控制方法研究;宋昭等;《锻压技术》;20151231;第40卷(第9期);第87-90页及图2-5 * |
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