DE102004010532A1 - Valve control of hydraulic actuators based on electrorheological fluids - Google Patents

Abstract

A valve control of hydraulic actuators, wherein the actuator has at least two via a flexible or movable element separate pressure medium spaces and wherein the pressure medium spaces are interconnected with four interconnected to a full bridge valves a, b, c, d on the basis of electrorheological / magnetorheological fluids is to be further developed be made possible that the control operations with extremely high dynamics. This is achieved by the fact that the valves can be controlled independently of each other, wherein as a control variable for the corresponding control q¶1¶, q¶2¶ and q¶q, 1¶ and q¶q, 2¶ and q¶q, 2¶ or q¶DELTA¶, q¶SIGMA¶ and q¶q, 1¶ and q¶q, 2¶ or q¶q, 1¶ and q¶q, 2¶ are used and from these manipulated variables the distribution of the valve volume flows q¶ a¶, q¶b¶, q¶c¶, q¶d¶ and thus the calculation of the voltage signals for the control of the valves a, b, c, d are calculated.

Description

In pneumatics and hydraulics become valves in switching and continuous valves divided. Continuous valves are valves in which the output (e.g. Valve spool travel, pressure, etc.) proportional to the input signal (e.g. Drive voltage) is. The operation can be done hand / mechanical / pressure / electric and electronic. Steady valves are also common referred to as proportional, control and servo valves, where the differences in the accuracy and use of the valves justify.

Farther There are valves based on electrorheological / magnetorheological liquids which are assigned to the class of continuous valves because of their characteristics can be.

In the conventional hydraulic is the control of a double acting cylinder generally via a 4/3 servo valve, the change the volume flow in the 4/3 servo valve done by an electromechanical transducer. The electromechanical Transducer (and the subsequent hydraulic intermediate stages) provides in general, the component limiting the dynamics of the valve represents.

The system, consisting of servo valve and cylinder, can be described here as a single-feed system with the input variable i _v (current through the servo valve) or with negligible dynamics of the servo valve x _v (position 4/3 servo valve) and the output variable s (position of the cylinder) become. The volume flows into the cylinder chambers q ₁ and q ₂ can not be used independently of each other as manipulated variables. Therefore, the mathematical model of the cylinder loses properties that prevent the applicability of certain controller design techniques.

Out The control theory are a variety of controller design methods for nonlinear Systems, known. For example, at this point the flatness-based Controller design (Joachim Rudolph: Contributions to the flatness-based Follow-up of linear and nonlinear systems finite and infinite Dimension, Shaker Verlag, 2003), the exact input state linearization (Alberto Isidori: Nonlinear Control Systems, 3rd edition, Springer Verlag 2001) and the passivity-based Controller design (Romeo Ortega et al .: Passivity Based Control of Euler-Lagrange Systems, Springer Verlag London 1998).

When controlled via a 4/3 servo valve, the chamber pressures p ₁ and p ₂ in the cylinder are adjusted so that in the steady state the force on the piston caused by the chamber pressures is equal to the load force. By contrast, the absolute values of the pressures p ₁ and p ₂ themselves can not be specifically influenced.

Farther are valves based on electrorheological and / or magnetorheological liquids known. Electrorheological valves are usually made of coaxial Cylindrical electrodes or constructed of arrangements of parallel plates, between which the electrorheological fluid flows. By electrical voltage applied to the electrodes or thereby generated electric field is the effective viscosity of between the electrorheological fluid located in the electrodes and thus the flow resistance through the valve gap controllable. In this case, with applied pressure difference, the flow through the valve of full opening (normal viscose Flow) until completely locked (Solid) be varied.

The Active principle is based on the fact that the particles of the electrorheological liquid form chains upon application of an electric field, which are the flow hinder and thus change the flow resistance.

• 1. Gavin, HP: Annular Poiseuille flow of ER and MR materials, Journal of Rheology, 45,4: 983-994, 2001;
• 2. Parthasarathy M, Klingenberg DJ: Electrorheology: Machanisms and Models, Journal of Materials, Science and Engineering R, reports; 17,2: 57-103, 1995;
• 3. Rajagopal KR, Wineman AS: Flow of electro-rheological materials, Acta Mechanica 91, 57-75, 1992;
• 4. Whittle M, Atkin RJ, Bullough WA: Dynamics of an electrorheological valve, International Journal of modern Physics B, 10, 23:2933-2950, 1996;
• 5. Růžička. M: Electrorheological Fluids: Modeling and Mathematical Theory. Lecture Notes in Mathematics, Springer Verlag, Berlin, 2000.

Compared to conventionally controllable valves valves based on electrorheological / magnetorheological fluids are simpler, because they have no moving mechanical parts such as shut-off. Another advantage is that electrical signals can be implemented directly, so that very fast switching times can be realized with electro-rheological fluid valves and thus a much higher dynamics of the overall system, for example consisting of cylinders with electrorheological valve, is achieved. However, a further complicating factor for a subsequent controller design is that the electrorheological effect is an inherently nonlinear phenomenon. In addition, hysteresis occurs in certain operating ranges. The electrorheological effect is described in more detail, for example, in the literature listed below:

• 1. Gavin, HP: Annular Poiseuille flow of ER and MR materials, Journal of Rheology, 45, 4: 983-994, 2001;
• 2. Parthasarathy M, Klingenberg DJ: Electrorheology: Machanisms and Models, Journal of Materials, Science and Engineering R, reports; 17,2: 57-103, 1995;
• 3. Rajagopal KR, Wineman AS: Flow of electro-rheological materials, Acta Mechanica 91, 57-75, 1992;
• 4. Whittle M, Atkin RJ, Bullough WA: Dynamics of an electrorheological valve, International Journal of Modern Physics B, 10, 23: 2933-2950, 1996;
• 5. Růžička. M: Electrorheological Fluids: Modeling and Mathematical Theory. Lecture Notes in Mathematics, Springer Verlag, Berlin, 2000.

In a known cylinder control of a cylinder, each cylinder chamber is associated with a half-bridge circuit consisting of two valves based on electrorheological and / or magnetorheological fluids: The four valves are connected to a full bridge, in the transverse branch of the hydraulic actuator (cylinder) is located. The control of these valves takes place in such a way that the four valves with a common average electrical voltage u and a differential voltage .DELTA.u are driven, ie at the valve a and d is the electrical voltage u + Δu, while at the valves b and c, the electrical voltage u - Δu is applied. The mean voltage u is chosen so that the valve works in a middle operating point. The voltage Δu now corresponds approximately to the position x _{v of} the 4/3 servo valve compared to conventional 4/3 servo valves. The electrorheological full bridge thus simulates the behavior of a 4/3-servo valve with an overlap, which with the help of u Both negative and positive can be set.

The disadvantage of this control and division, however, is that not all degrees of freedom of the full bridge are used, with the consequence that, for example, a compensation of the non-linearity of the valves inherently occurring due to the electrorheological effect is impossible. In the above-described control of the valves based on electrorheological / magnetorheological fluids, the volume flows into the cylinder chambers q ₁ / q _{2 are} also not used independently of each other as a manipulated variable. For this reason, the mathematical model of the cylinder and the full bridge (consisting of electrorheological valves) loses properties that prevent the applicability of certain rule design methods. For example, it can be shown that the flatness-based controller design and the exact input state linearization are no longer applicable.

The mentioned disadvantages have the consequence that with electrorheological Actuators achievable control performance and dynamics no visible advantage over classic hydraulic actuators with 4/3 servo valve.

The Object of the present invention is the above-mentioned To prevent disadvantages and a valve control for actuators based on electrorheological fluids to create the Control and regulation processes with extremely high dynamics.

This object is achieved in that the valves associated with the actuator are independently controllable. For the actuation of the valves in a full bridge circuit, the virtual manipulated variables q ₁ , q ₂ and q _{q, 1} and q _{q, 2} or q _Δ , q _Σ and q _{q, 1} and q _{q, 2} for the Division of the valve volume flows q _a , q _b , q _c , q _d based.

On the basis of the aforementioned control variables, which are much better suited for the controller design, the 4 electrical voltages for the control of the 4 valves are calculated. With the help of the new manipulated variables q ₁ and q _2, it is very easy to control the chamber pressures. q _{q, 1} and q _{q, 2} serve as control variables for the supply pressure control and prevent the valves from being completely blocked as they ensure a minimum volume flow. q _Σ and q _Δ are used as manipulated variables for the decoupled control of the total pressure and the position or speed of the piston. Due to the independent specifications of the aforementioned manipulated variables, all linear and / or non-linear and / or adaptive single and multi-variable control methods with or without cascade structure can be used.

Since all the valves associated with the actuator are always flowed through with a minimum volume flow (q _{q, 1} or q _{q, 2} ), there are no undesirable hysteresis effects and the advantages of the technology based on electrorheological / magnetorheological fluids, ie the advantages of the fast reaction time and thus the higher dynamics are meaningfully usable.

Also advantageous is the possibility of regulating the supply pressure by means of the manipulated variables of the minimum volume flow q _{q, 1} / q _{q, 2} . This makes it possible to dispense with the arrangement of the otherwise necessary pressure control valve in the pressure supply.

In addition exists now the possibility To adjust the supply pressure very easily variable in time.

The above object is further achieved in that the associated with an actuator, connected to a half-bridge, valves are independently controllable and for the control of the manipulated variables q ₁ and q _{q, 1} for the distribution of the valve volume flows q _a and q _b basis become.

1 shows a schematic diagram of an actuator 1 based on electrorheological fluids consisting of a cylinder 2 in the crossbar 3 one of four valves a, b, c, d based on electrorheological / magnetorheological fluids full bridge is connected. The cylinder 2 is shown in the embodiment as a synchronous cylinder, but it could be used from any other cylinder design.

The cylinder 2 has a cylinder housing 4 with an axially displaceably mounted piston 5 on. The piston 5 divides the cylinder housing 4 in a first and a second volume variable working chamber 6 . 6 ' , In the cylinder housing 4 in each case an inlet / outlet opening for the pressure medium is introduced. The inlet / outlet opening of the first and second working chamber 6 . 6 ' is in each case with one in the transverse branch 3 the valve full-bridge circuit arranged fluid line 7 . 7 ' coupled. Every working chamber 6 . 6 ' of the cylinder 2 Thus, a Hall bridge circuit consisting of two valves a, b / c, d assigned based on electrorheological / magnetorheological fluids. The first working chamber 6 associated valves a, b are, as can be seen from the illustrations, in a first longitudinal branch 8th arranged the full bridge circuit. The second working chamber 6 ' associated valves c, d are in a second longitudinal branch 8th' arranged the full bridge circuit. The full bridge circuit of the valves a, b, c, d is between the fluid connection of the valves a, c with a supply pressure line 9 connected. The supply pressure is provided via a pump / storage arrangement not described in detail here. Since, in principle, only one volume flow in the direction of the pressure difference can flow in the case of valves based on electrorheological / magnetorheological fluids, the above-described interconnection to a full bridge is necessary. The flow direction of the volume flows is in the 1 represented by the arrows. The valves b, d are with a tank 10 coupled.

valves based on electrorheological / magnetorheological fluids are in a variety of embodiments known.

The valve based on electrorheological fluids consists in principle of a valve gap formed in a housing, which is bounded by electrically controllable electrode arrangements, so that an electrorheological fluid flowing through the valve gap can be changed by changing the electric field generated between the electrode arrangements with regard to the rheological properties. With the help of an impressed by a high voltage amplifier voltage to the electrode assemblies, an electric field can be generated and thus, with applied pressure difference, the volume flow through the valve can be varied. The valve thus represents an electrically adjustable throttle, which is shown schematically in the drawing of 1 is shown.

It is self-evident at this point, that when using magnetorheological fluids Instead of electrode arrangements coil arrangements for the production a magnetic field must be provided.

An essential feature of the invention is that the four degrees of freedom of the valves a, b, c, d based on electrorheological / magnetorheological fluids are optimally utilized in the full bridge. By using the volume flows in the first and second working chamber q ₁ , q ₂ as independent control variables, the pressures in the two working chambers can be regulated. This can also be used as a subordinate control loop in a cascade controller structure, while the actual controlled variable (for example the position of the cylinder s or the pressure force) is regulated in a superimposed control loop.

q_a

= Volumenstrom durch das Ventil a

q_b

= Volumenstrom durch das Ventil b

q_c

= Volumenstrom durch das Ventil c

q_d

= Volumenstrom durch das Ventil d

From the schematic representation of 1 It can be seen that the volume flows q ₁ , q ₂ to and from the working chambers in each case from the difference of the valve volume flows of the first and second longitudinal branches 8th . 8th' to form the full bridge: q 1 = q a - q b 1.) q 2 = q c - q d 2.)

q _a

= Flow through the valve a

q _b

= Volume flow through the valve b

q _c

= Volume flow through the valve c

q _d

= Volume flow through the valve d

As already explained in more detail above, hysteresis effects occur in the transition region to completely block the valve based on electrorheological fluids. To prevent this, the valves a, b, c, d are always operated with a minimum volume flow. It is essential that the minimum volume flow through the valves a and b (q _{q, 1} ) and c and d (q _{q, 2} ) are the same size, because then the volume flows q ₁ and q ₂ are not affected. The minimum volume flow through the first longitudinal branch 8th is subsequently with q _{q, 1} , the minimum volume flow through the second longitudinal branch 8th' denoted by q _q , ₂ .

If the volume flows q ₁ / q ₂ are now used as manipulated variables, then the volume flows are distributed among the four valves a, b, c, d of the full bridge as follows:

there the value of the function q (q) for positive q corresponds to the argument q, while the value for negative q is identical to 0.

With a symmetrical bridge, it makes sense to select q _{q, 1} and q _{q, 2 the} same size. It follows immediately from the above drive strategy that q _a ≥ q _{q, 1} , q _b ≥ q _{q, 1} , q _c ≥ q _{q, 2} and q _d ≥ q _{q, 2} , and thus the valves are never completely disabled.

On The basis of the four valve volume flows (and associated pressure drops) can now the electrical voltages of the valves are clearly defined. The four electrical voltages at the valves are the actual ones Manipulated variables of the Actuator.

mit dem Summenvolumenstrom q_Σ, dem Differenzvolumenstrom q_Δ, sowie den Arbeitskammervolumina (für s=0) V₀₁ und V₀₂ und den effektiven Kolbenflächen A₁ und A₂ des Kolbens zu parametrieren. Die Terme V₀₁ + A₁s und V₀₂ – A₂s dienen dazu, die durch die Stellung des Kolbens s bedingte Nichtlinearität durch die unterschiedlichen Volumina in den beiden Kammern zu kompensieren. Mit dieser Gleichung werden sämtliche Bauformen, wie Gleichgangzylinder (A1 = A2), Zweistangenzylinder mit unterschiedlicher Kolbenfläche oder Differenzialzylinder erfasst. Falls die durch diese Terme bedingten Nichtlinearitäten keinen besonders großen Einfluss auf das dynamische Verhalten haben, beispielsweise wenn der Weg des Kolbens s sehr klein ist, können diese in der Gleichung auch entfallen.For example, if you want to know the position of the piston 5 of the cylinder 2 and the total pressure or the force on the piston 5 and regulate the total pressure or other equivalent quantities, it makes sense, the volume flows q ₁ and q ₂ as follows:

with the sum volume flow q _Σ , the differential volume flow q _Δ , and the working chamber volumes (for s = 0) V ₀₁ and V ₀₂ and the effective piston areas A ₁ and A _{2 of} the piston to parameterize. The terms V ₀₁ + A ₁ s and V ₀₂ - A ₂ s serve to compensate for the nonlinearity due to the position of the piston s due to the different volumes in the two chambers. With this equation, all types, such as synchronous cylinder (A1 = A2), two-rod cylinder with different piston area or differential cylinder are detected. If the non-linearities caused by these terms do not have a particularly great influence on the dynamic behavior, for example if the travel of the piston s is very small, these can also be omitted in the equation.

The above-mentioned manipulated variable transformation now has the advantage that with the sum volume flow q _Σ directly the total pressure and with the differential volume flow q _Δ directly the position or velocity of the piston or the force on the piston can be decoupled influenced.

For the new virtually formed manipulated variables q _Σ , q _Δ , the distribution of the volume flows to the four valves a, b, c, d of the full bridge takes place as follows:

On the basis of the four valve flow rates q _a, q _b, q _c, q _d can now electric voltages for controlling the four valves a, b, c, d are clearly defined.

In 2 is shown in a schematic representation of the entire control concept. In the controller (designed by known controller throwing methods) 11 are the manipulated variables q _{q, 1} , q _{q, 2} and the manipulated variables q ₁ , q ₂ or q _Σ and q _Δ , as further defined above in the text formed. In the block valve control 12 are selected from the predetermined set sizes, the valve flow rates q _a, q _b, q _c, q _d through the above-mentioned equations in response to the manipulated variables used q ₁ and q ₂ or q calculated _Σ and _Δ q.

In a subsequent stress calculation 13 From the valve volume flows, the corresponding voltages of the valves a, b, c, d are calculated. These values (the real manipulated variables) become the high-voltage amplifier 14 fed. The valves (shown here by block 15 ) are now controlled according to the calculated voltages, so that the previously calculated valve volume flows q _a , q _b , q _c , q _d set and the first working chamber 6 with the volume flow q ₁ and the second working chamber 6 ' be charged with the flow q ₂ .

to Implementation of an actuating law is generally a measurement or observation (in the sense of control engineering) of certain system sizes necessary. Which system sizes for the control are generally essential to the chosen controller concept dependent. For the proposed control of electrorheological valves is in any case the knowledge of the pressure drop along the individual Valves necessary.

The pressures p ₁ and p ₂ in the working chambers, which adjust as a function of the volume flows g ₁ and q ₂ 6 . 6 ' , which are hereinafter referred to as state variables, are in or on the cylinder 2 detected, ie measured or monitored by means of appropriate sensors. The recorded state variables 16 like pressures, way of the piston and / or speed or forces are used as actual variables to the regulator 11 supplied and compared with the predetermined setpoints. A corresponding control deviation is corrected accordingly.

In the schematic diagram is as a block 17 the pressure supply shown. The valve full bridge circuit 15 is with the specified supply volume flow 18 supplied via the supply pressure line.

It goes without saying that the valve control according to the invention of hydraulic actuators which has been described above with reference to a full-bridge circuit can also be used for a half-bridge circuit. In this case, only q ₁ for a working chamber / pressure medium chamber and q _{q, 1} can be used as manipulated variables as the minimum volume flow of the longitudinal branch of the half bridge. From these manipulated variables, the distribution of the volume flows for the valves a and b in q _a and q _{b takes place} analogously.

in principle can as an actuator in place of the previously described cylinder-piston assembly Arrangements may also be provided which delimit by means of a membrane Pressure medium spaces exhibit.

Claims (2)

Valve control of hydraulic actuators, wherein the actuator has at least two separate via an elastic or movable element pressure medium spaces and wherein the pressure medium spaces with four to a full bridge interconnected valves a, b, c, d are linked on the basis of electrorheological / magnetorheological fluids and wherein the valves are independently controllable, where as a manipulated variable for the corresponding control q ₁ , q ₂ and q _{q, 1} and q _{q, 2} or q _Δ , q _Σ and q _{q, 1} and q _{q, 2} or q _{q, 1} and q _{q, 2} are used and from these manipulated variables, the distribution of the valve volume flows q _a , q _b , q _c , q _d and thus the Calculation of the voltage signals for the control of the valves a, b, c, d are calculated. Valve control of hydraulic actuators wherein the actuator has at least one via a flexible or movable element separate pressure medium space, and wherein the pressure medium space is connected to two connected to a half-bridge valves a, b based on electrorheological / magnetorheological fluids, and wherein the valves a, b independently can be controlled from each other, being used as a manipulated variable for the corresponding control q ₁ and q _{q, 1} or q _{q, 1} and from these manipulated variables, the distribution of the valve volume flows q _a , q _b and thus the calculation of the voltage signals for the control of the valves a , b are calculated.