Pneumatic position control system and method

Abstract

The invention relates to a pneumatic position control system for an actuator member, comprising a pneumatic actuator, which comprises the actuator member and a first pressure chamber and a second pressure chamber, and a valve device, which has a first working output pneumatically connected to the first pressure chamber and a second working output pneumatically connected to the second pressure chamber, and is designed to separately adjust respective compressed air mass flows at the working outputs as part of the position control, in order to pneumatically actuate the first pressure chamber and the second pressure chamber and thus position the actuator member, wherein the pneumatic system has a position control device, which is designed to generate a mass flow specification signal underlying the compressed air mass flows, and a mean-pressure control unit which is designed to carry out pressure control of a mean pressure of the first pressure chamber and second pressure chamber as part of the position control.

Description

[0001] Festo SE & Co. KG, Ruiter Straße 82, 73734 Esslingen

[0002] Pneumatic system for position control and movement

[0003] The invention relates to a pneumatic system for controlling the position of an actuator element. The pneumatic system comprises a pneumatic actuator, which includes the actuator element and a first pressure chamber and a second pressure chamber. The pneumatic system further comprises a valve device having a first working outlet pneumatically connected to the first pressure chamber and a second working outlet pneumatically connected to the second pressure chamber.

[0004] The pneumatic actuator, for example, is a double-acting drive cylinder. The actuator element is, for example, the piston (or a piston assembly including the piston) of the drive cylinder.

[0005] The pneumatic system is used, in particular, to position a positioning object, for example a wafer, in particular a semiconductor wafer, by positioning the actuator element. The pneumatic system is used, in particular, in industrial automation. For example, the pneumatic system is part of a semiconductor factory, in particular a chip factory.

[0006] J. -J. Slotine and W. Li, "Applied Nonlinear Control," Prentice Hall, 1991, describes the principle of feedback linearization in Chapter 6. One object of the invention is to enable high-accuracy position control in an efficient manner.

[0007] The object is achieved by the pneumatic system according to claim 1. The valve device of the pneumatic system is designed to set respective compressed air mass flows separately at the working outputs as part of the position control in order to pneumatically actuate the first pressure chamber and the second pressure chamber and thereby position the actuator element. The valve device has a position controller device which is designed to generate a mass flow specification signal underlying the compressed air mass flows, and also has a center pressure controller unit which is designed to carry out pressure control of a center pressure of the first pressure chamber and second pressure chamber as part of the position control.

[0008] Preferably, the valve device is capable of independently adjusting respective compressed air mass flows at the working outlets, which may differ from one another, in particular in their magnitudes. For example, the valve device has two independent valve units, each valve unit providing a respective working outlet.

[0009] The formulation that the mass flow target signal forms the basis for the compressed air mass flows means in particular that the compressed air mass flows depend on the mass flow target signal.

[0010] The mean pressure of the first pressure chamber and the second pressure chamber represents a common pressure level of both pressure chambers. The mean pressure can be calculated, for example, as the average of the pressure in the first pressure chamber and the pressure in the second pressure chamber.

[0011] Because the two compressed air mass flows can be adjusted independently of one another and because mean pressure control is carried out, it can be achieved in particular that there is an integral behavior of a compressed air mass flow to a pressure of the pneumatic actuator - i.e. in particular that the pressure (for example a pressure in a pressure chamber or a differential pressure between the pressure chambers) corresponds to the integral of one or both of the compressed air mass flows (in particular of a target mass flow signal underlying a compressed air mass flow), for example is proportional to the integral and / or can be calculated on the basis of the integral. This makes it possible to reduce the requirements placed on the position controller device. In particular, in this case the position controller device itself does not need to have an I component (integral component), i.e. in particular no I element.In addition, the pressure control of the center pressure can ensure that the position control device only has to be designed for a specific pressure level range of the pneumatic actuator, which also reduces the requirements for the position control device.

[0012] Advantageous further training is the subject of dependent claims.

[0013] The position controller device preferably comprises a position controller unit which is designed to generate a position controller signal which in particular defines a compressed air mass flow. The position controller device preferably also comprises a linearization unit which is designed to generate the mass flow specification signal on the basis of the position controller signal, taking into account a non-linear model of the pneumatic actuator. The linearization unit is particularly designed to transform a non-linear model of the pneumatic actuator into a linear model in the center position (of the actuator element). The center position is a position of the actuator element in which the actuator element is positioned centrally between its two end positions (e.g. a maximum extended position and a maximum retracted position).Due to the linearization unit, the position controller unit can generate the position controller signal as if the behavior (in particular the pneumatic behavior) of the pneumatic actuator always corresponded to the state in which the actuator element is in the center position; thus, when generating the position controller signal, the position controller unit does not have to take into account any non-linearities that arise, for example, because the actuator element is outside the center position and the volumes of the pressure chambers (and / or the pneumatic behavior of the pneumatic actuator) are changed in this state.The linearization unit converts the position controller signal into the mass flow setpoint signal in such a way that the mass flow setpoint signal has the same effect in the current position of the actuator element—in particular, it causes the same mass flows into / out of the pressure chambers—as the position controller signal would in the center position of the actuator element. In this way, the requirements for the position controller unit can be reduced.

[0014] Preferably, the linearization unit is designed to convert the position controller signal into the mass flow specification signal within the scope of a linearization, in particular a feedback linearization, so that for the position controller unit, a position control loop section of the position control comprising the linearization unit and the pneumatic actuator functions (in particular appears) as a linear control system, in particular as a linear control system in which the actuator element is in the center position or is calculated.

[0015] The center pressure regulator unit is preferably designed to calculate target mass flow signals based on the mass flow specification signal as part of the pressure control of the center pressure, wherein the target mass flow signals form the basis for the pneumatic actuation of the pressure chambers. For example, a first target mass flow signal is calculated based on the mass flow specification signal, according to which a first compressed air mass flow to the first pressure chamber is set, and a second target mass flow signal is calculated based on the mass flow specification signal, according to which a second compressed air mass flow to the second pressure chamber is set. The compressed air mass flows are preferably not set as part of a mass flow control, i.e. in particular without using a mass flow sensor.

[0016] Preferably, the valve device is designed to adjust the compressed air mass flows as part of the position control such that an integral behavior of a compressed air mass flow to a pressure assigned to the pneumatic actuator is given. The compressed air mass flow is in particular the compressed air mass flow into the first pressure chamber or into the second pressure chamber. The pressure is in particular a pressure in the first pressure chamber or in the second pressure chamber, or a differential pressure between the first pressure chamber and the second pressure chamber. For example, the integral of the compressed air mass flow results in a compressed air mass, and the pressure assigned to the pneumatic actuator is linked to the compressed air mass, for example via the general gas equation, and / or is proportional to the compressed air mass.

[0017] The position controller device is preferably designed to provide a position controller signal / the position controller signal underlying the mass flow specification signal without an I component (integral component). The controlled system—in particular the pneumatic actuator—suitably exhibits integral behavior, so that a pure P feedback (proportional feedback)—in particular a position controller unit designed as a P controller (proportional controller) and / or a position controller element of the position controller unit designed as a P controller—can achieve steady-state accuracy in the position control of the actuator element, in particular without an I component in the position controller unit and / or the position controller element. An I component in the controller can ensure steady-state accuracy during control. However, in conjunction with friction, an I component in a position controller unit can lead to limit cycles.By providing the position controller signal (and / or the mass flow command signal) without an I component, the risk of limit cycles can be reduced or avoided.

[0018] The valve device preferably comprises a differentiator unit configured to generate an actual acceleration signal based on a detected position of the actuator element, wherein the position controller device is configured to generate the mass flow specification signal taking the actual acceleration signal into account. The position controller device, in particular the position controller element, is expediently designed as a state controller with acceleration feedback. In this way, the interference stiffness can be increased.

[0019] Preferably, due to the consideration of the actual acceleration signal, an integral behavior of a / the pressure assigned to the pneumatic actuator to the position of the actuator element is given. The pressure assigned to the pneumatic actuator is in particular the pressure of the first pressure chamber, the pressure of the second pressure chamber, or the differential pressure between the first pressure chamber and the second pressure chamber. Preferably, the position controller device is designed to generate the position controller signal without taking into account an actual pressure signal related to the pneumatic actuator, in particular without taking into account any pressure signal. The actual pressure signal describes, for example, the pressure in the first pressure chamber, the pressure in the second pressure chamber and / or a differential pressure between the first pressure chamber and the second pressure chamber.The above-mentioned integral behavior of the pressure to the position of the actuator element can be achieved in particular by feeding back the acceleration of the actuator element to the position controller unit as part of the position control, and in particular no pressure of the pneumatic actuator.

[0020] The valve device preferably comprises a first valve unit, which provides the first working output, and a second valve unit, which provides the second working output. The first valve unit and the second valve unit each expediently function as 3 / 3-way valves. Each valve unit is expediently able to selectively ventilate, vent or block its respective working output (in particular independently of the other valve unit). In particular, the valve units function as proportional valves. In particular, the valve device does not comprise a 5 / 3-way valve for pneumatically actuating the pneumatic actuator.

[0021] The valve device preferably comprises a bridge circuit comprising four 2 / 2-way valves that provides the two working outputs. The 2 / 2-way valves are designed, in particular, as (preferably proportional) piezo valves.

[0022] The position controller device preferably comprises a / the position controller unit which is designed to calculate a / the position controller signal, on the basis of which the position controller device calculates the mass flow specification signal, wherein the position controller unit comprises a position controller element for calculating a position controller element signal and an accuracy controller element for calculating an accuracy controller signal, and is designed to calculate the position controller signal based on the position controller element signal and the accuracy controller signal. The accuracy controller element can also be referred to as an additional controller element and the accuracy controller signal as an additional signal.

[0023] Preferably, the position controller element has one or more gain factors for calculating the position controller element signal and the accuracy controller element has one or more gain factors for calculating the accuracy controller signal, wherein each gain factor of the accuracy controller element is greater than each gain factor of the position controller element.

[0024] Preferably, the accuracy control element has a limiting device for limiting the accuracy control signal.The invention further relates to a method for controlling the position of an actuator element of a pneumatic actuator which comprises a first pressure chamber and a second pressure chamber, wherein a valve device which has a first working outlet pneumatically connected to the first pressure chamber and a second working outlet pneumatically connected to the second pressure chamber, separately sets respective compressed air mass flows at the working outlets as part of the position control in order to pneumatically actuate the first pressure chamber and the second pressure chamber and thereby position the actuator element, wherein the valve device has a position control device which generates a mass flow preset signal underlying the compressed air mass flows, and a center pressure control unit which carries out pressure control of a center pressure of the first pressure chamber and second pressure chamber as part of the position control.

[0025] Further exemplary details and exemplary embodiments are explained below with reference to the figures.

[0026] Figure 1 is a schematic representation of a pneumatic system, and

[0027] Figure 2 shows a block diagram of a position control,

[0028] Figure 3 is a block diagram of a position control according to a further variant, and

[0029] Figure 4 is a block diagram of an accuracy control element.

[0030] Figure 1 shows an exemplary embodiment of a pneumatic system 1 for controlling the position of an actuator element 2. The pneumatic system 1 is particularly suitable for use in industrial automation.

[0031] The pneumatic system 1 comprises a pneumatic actuator

[0032] 3 , which comprises the actuator member 2 as well as a first pressure chamber 4 and a second pressure chamber 5 . By means of pneumatic actuation of the first pressure chamber 4 and / or the second pressure chamber 5 , the actuator member 2 can be set in motion . By way of example, the pneumatic actuator 3 is designed as a pneumatic drive cylinder . The pneumatic actuator 3 expediently comprises an actuator housing 6 , relative to which the actuator member 2 is movable , in particular by pneumatic actuation of one or both pressure chambers

[0033] 4, 5. The first pressure chamber 4 and the second pressure chamber 5 are arranged in the actuator housing 6. The actuator member 2 is designed, for example, as a piston arrangement and comprises, for example, a piston and, expediently, a piston rod fastened to the piston.

[0034] For example, pneumatic actuator 3 is a linear pneumatic drive. Alternatively, the pneumatic actuator can also be designed as a rotary pneumatic drive.

[0035] By way of example, the pneumatic system 1 comprises a positioning object 7 to be positioned by means of the actuator element 2. The positioning object 7 is, by way of example, coupled in terms of movement to the actuator element 2. The positioning object 7 is, for example, a wafer, in particular a semiconductor wafer.

[0036] The pneumatic system 1 expediently comprises a position detection unit 22, which serves to detect a position of the actuator element 2, in particular along a movement path from a first end position to a second end position of the actuator element. The position detection unit 22 comprises, for example, a magnetic sensor device for detecting a magnetic field of a magnet arranged on the actuator element 2.

[0037] The pneumatic system 1 further comprises a valve device 8 for pneumatically actuating the pneumatic actuator 3. The valve device 8 shall in particular refer to the entirety of the valves involved in the pneumatic actuation of the pneumatic actuator 3, as well as the control components that control these valves. The entirety of these valves shall hereinafter be referred to as the valve device, and the entirety of the control components shall be referred to as the control device 19. If a PLC is involved in the control, this shall in particular also be regarded as part of the valve device 8.

[0038] The pneumatic system 1 expediently comprises a compressed air source 15 and / or a compressed air sink 16 (for example the environment of the valve device 8).

[0039] The valve device 8 has a first working outlet 9 and a second working outlet 10. The working outlets 9, 10 are designed, for example, as hose connections. The first working outlet 9 is pneumatically connected to the first pressure chamber 4, for example via a first pneumatic line 11, in particular a first hose. The second working outlet 10 is pneumatically connected to the second pressure chamber 5, for example via a second pneumatic line 12, in particular a second hose. The working outlets 9, 10 can each optionally output compressed air (in particular provided by the compressed air source 15) or take in compressed air (in particular to be discharged to the compressed air sink 16).

[0040] The valve device 8 comprises the valve means, which is designed as a bridge circuit, in particular as a pneumatic full bridge. The valve device comprises, for example, a first valve unit (designed in particular as a first half-bridge), which provides the first working outlet 9, and a second valve unit (designed in particular as a second half-bridge), which provides the second working outlet 10. The first valve unit and the second valve unit expediently each function as 3 / 3-way valves. By means of the first valve unit, the first working outlet 9 (and thus the first pressure chamber 4) can be selectively ventilated, vented or blocked. By means of the second valve unit, the second working outlet 10 (and thus the second pressure chamber 5) can be selectively ventilated, vented or blocked. As mentioned above, the valve device is designed as a bridge circuit, for example.The bridge circuit provides the two working outputs 9, 10 and comprises, for example, four valves 14, which are designed in particular as 2 / 2-way valves. The valves 14 are preferably designed as proportional valves and / or piezo valves.

[0041] By way of example, the valve device comprises a first valve 14a which is pneumatically connected between the compressed air source 15 of the pneumatic system 1 and the first working outlet 9. By way of example, the valve device comprises a second valve 14b which is pneumatically connected between the compressed air sink 16 of the pneumatic system 1 and the first working outlet 9. By way of example, the valve device comprises a third valve 14c which is pneumatically connected between the compressed air source 15 and the second working outlet 10. By way of example, the valve device comprises a fourth valve 14d which is pneumatically connected between the compressed air sink 16 and the second working outlet 10.

[0042] The valve device 8 is designed to carry out a position control of the actuator element 2 and, as part of the position control, to separately set respective compressed air mass flows 46, 47 at the working outlets 9, 10 in order to pneumatically actuate the first pressure chamber 4 and the second pressure chamber 5 and thereby position the actuator element 2. In particular, the valve device 8 sets the first compressed air mass flow 46 at the first working outlet 9, which flows for example from the first working outlet 9 into the first pressure chamber 4 and / or sets the second compressed air mass flow 47 at the second working outlet 10, which flows for example from the second pressure chamber 5 to the second working outlet 10.

[0043] The pneumatic system 1 preferably comprises a pressure sensor device which serves to detect a first air pressure assigned to the first pressure chamber 4 and a second air pressure assigned to the second pressure chamber 5. The assigned air pressure should in particular be referred to as an air pressure which corresponds to the air pressure in the respective pressure chamber or from which the air pressure in the respective pressure chamber can be calculated. By way of example, the pressure sensor device has a first pressure sensor 17 which is arranged in particular at the first working outlet 9 and / or a second pressure sensor 18 which is arranged in particular at the second working outlet 10. By way of example, the pressure sensors 17, 18 are part of the valve device. Furthermore, the pressure sensors 17, 18 can be arranged on the pneumatic lines 11, 12 and / or in or on the pressure chambers 4, 5.

[0044] The valve device 8 further comprises the control device 19, which serves to control the valve device. The control device 19 can comprise a control unit 20 and / or a controller 21.

[0045] The control unit 20 is designed, for example, as a microcontroller. Preferably, the valve device 8 comprises a valve module, and the control unit 20 and the valve device are part of the valve module. The control device 19, in particular the control unit 20, is expediently designed to control the valves 14 (in particular electrically) and / or to communicate with the pressure sensors 17,

[0046] 18 to record the air pressures assigned to the pressure chambers 4 , 5 .

[0047] The control device 19 optionally comprises the controller 21, which is designed, for example, as a higher-level controller, in particular as a PLC (programmable logic controller). The controller 21 is communicatively connected to the control unit 20, for example. The control device 19, in particular the control unit 20 and / or the controller 21, expediently serves to detect the position of the actuator element 2 with the position detection unit 22.

[0048] With reference to Figure 2, a position control carried out by the pneumatic system 1 will be explained below, which is carried out in particular by the control device

[0049] 19 is carried out. The units involved in the position control explained below (except for the actuator device 40) are expediently implemented as software that is executed on the control device 19, in particular the controller 21 and / or the control unit 20. It should be noted that the units implemented as software are preferably to be understood as purely functional, i.e. in particular as calculation functions that can be provided, for example, as an individual function block and / or combined in function blocks.

[0050] The control device 19 comprises a target position generation unit 23, which is designed to generate a target position signal 24. The target position signal 24 specifies a target position for the actuator element 2. Preferably, the target position signal 24 specifies a trajectory—in particular, a temporal position profile—for the actuator element 2. Optionally, the target position generation unit 23 further generates a target speed signal 49 and / or a target acceleration signal 50 and / or a target jerk signal. The target position generation unit 23 is preferably implemented on the controller 21.

[0051] The control device 19 comprises a position controller 25, which receives the desired position signal 24 (and optionally the desired speed signal 49 and / or the desired acceleration signal 50 and / or the desired jerk signal). The position controller 25 is designed to generate a mass flow specification signal 36, which forms the basis of the compressed air mass flows 46, 47. The position controller 25 is expediently designed as a state controller with acceleration feedback. The acceleration feedback expediently increases the disturbance stiffness. The position controller 25 is preferably designed to generate the mass flow specification signal 36 taking into account the actual acceleration signal 45. Due to the consideration of the actual acceleration signal 45, an integral behavior of a pressure assigned to the pneumatic actuator 3 to the position of the actuator element 2 is expediently given.

[0052] The position controller device 25 comprises a position controller unit 26 and preferably a linearization unit 27.

[0053] By way of example, the position controller unit 26 comprises a subtraction element 28, a position controller element 29 and optionally a pilot control element 30 and / or an addition element 51.

[0054] The position controller unit 26 is designed to generate a position controller signal 31 that defines a compressed air mass flow. For example, the position controller signal 31 specifies the first compressed air mass flow 46 and / or the second compressed air mass flow 47. In particular, the position controller signal 31 can specify an amount of the first compressed air mass flow 46 and / or the second compressed air mass flow 47. For example, the position controller signal 31 specifies the same amount for both compressed air mass flows 46, 47 (and the two compressed air mass flows 46, 47 then have, for example, different signs or directions). The position controller signal 31 is preferably a scalar signal.

[0055] The linearization unit 27 is designed to generate, in particular calculate, the mass flow specification signal 36 based on the position controller signal 31, taking into account a non-linear model of the pneumatic actuator 3. Preferably, the linearization unit 27 transforms the complete non-linear model of the pneumatic actuator 3 into a linear model in the center position using a modified exact input / output linearization. The position controller unit 26 is expediently designed for the transformed, linear center position model. The mass flow specification signal 36 is preferably a scalar signal.

[0056] When generating the mass flow specification signal 36, the linearization unit 27 expediently takes into account an actual position signal 32 (related to the actuator element 2), an actual speed signal 44 (related to the actuator element 2), a first actual pressure signal 41 (related to the first pressure chamber 4) and / or a second actual pressure signal 42 (related to the second pressure chamber 5).

[0057] In particular, the linearization unit 27 models a current state of the pneumatic actuator 3, in particular related non-linearities of the pneumatic actuator 3, on the basis of the actual position signal 32, actual speed signal 44 and the actual pressure signals 41, 42, in order to expediently generate the mass flow specification signal 36 such that it has the same effect for the pneumatic actuation of the pneumatic actuator 3 (for example for the compressed air mass flows 46, 47) as the position controller signal 31 underlying the mass flow specification signal 36 would have in a state in which the actuator element 2 is in a center position.

[0058] By way of example, the position controller unit 26 calculates the position controller signal 31 on the basis of the desired position signal 24 (and optionally the desired speed signal and / or the desired acceleration signal and / or the desired jerk signal) and on the basis of an actual position signal 32 (and optionally an actual speed signal 44 and / or an actual acceleration signal 45).

[0059] Preferably, the position controller device 25 is designed to provide the position controller signal 31 underlying the mass flow specification signal 36 without an I component.

[0060] Preferably, the position controller device 25 is configured to generate the position controller signal 31 without taking into account an actual pressure signal 41, 42 related to the pneumatic actuator 3. In particular, no actual pressure signal 41, 42 is fed back to the position controller unit 26. By not feeding back an actual pressure signal related to the pneumatic actuator 3 to the position controller unit 26, an integral behavior of the system can be achieved.

[0061] The subtractor 28 calculates a difference between the desired position signal 24 and the actual position signal 32 (and optionally between the desired speed signal 49 and the actual speed signal 44 and / or between the desired acceleration signal 50 and the actual acceleration signal 45). The subtractor 28 provides the one or more calculated differences as one or more deviation signals 33.

[0062] The position controller element 29 calculates a position controller element signal 34 based on the one or more deviation signals 33, in particular in such a way as to achieve a (magnitude-based) reduction of the one or more deviation signals 33. By way of example, the position controller element 29 has a P-element for calculating the position controller element signal 34.

[0063] The pilot control element 30 calculates a pilot control signal 35 based on the desired position signal 24 (and optionally the desired speed signal 49 and / or the desired acceleration signal 50 and / or the desired jerk signal). The pilot control element 30 expediently has

[0064] On switching amplifications with which the pilot control element 30 calculates the pilot control signal 35.

[0065] The addition element 51 calculates the position controller signal 31 on the basis of, in particular as a sum of, the position controller element signal 34 and the pilot control signal 35.

[0066] According to an alternative embodiment (in which in particular the pilot control element 30 and the addition element 51 are not present), the position controller element signal 34 is used as the position controller signal 31.

[0067] The valve device 8 has a center pressure regulator unit 37 which is designed to carry out pressure control of a center pressure of the first pressure chamber 4 and the second pressure chamber 5 as part of the position control.

[0068] For example, the center pressure regulator unit 37 calculates target mass flow signals 38 based on the mass flow specification signal 36 and taking into account one or more actual pressure signals 41, 42 relating to the pressure chambers 4, 5. The target mass flow signals 38 form the basis for the pneumatic actuation of the pressure chambers 4, 5. In particular, the center pressure regulator unit 37 generates a first target mass flow signal that specifies a target value for the first mass flow relating to the first pressure chamber 4, and a second target mass flow signal that specifies a target value for the second mass flow relating to the second pressure chamber 5.

[0069] Conveniently, the center pressure regulator unit 37 generates the target mass flow signals 38 such that an actual center pressure of the two pressure chambers 4, 5 is changed toward a target center pressure. Preferably, the center pressure regulator unit 37 calculates the actual center pressure based on the actual pressure signals 41, 42, in particular as the mean value of the two actual pressure signals 41, 42.

[0070] Preferably, the center pressure regulator unit 37 generates the target mass flow signals 38 such that the first compressed air mass flow 46 is equal to the negative second compressed air mass flow 47, provided no adjustment of the actual center pressure is required (for example, if the actual center pressure corresponds to the target center pressure). The magnitude of the first target mass flow signal and / or the second target mass flow signal is expediently specified by the mass flow specification signal 36 or corresponds to it (in particular weighted according to the respectively assigned piston area of ​​the actuator element 2 and / or in particular in the case in which no adjustment of the actual center pressure is required).

[0071] The piston area of ​​the actuator element 2 which delimits the respective associated pressure chamber 4, 5 shall be referred to as the assigned piston area.

[0072] Optionally, the center pressure regulator unit 37 takes into account the actual position signal 32 and / or the actual speed signal 44 when calculating the target mass flow signals 38. For example, the center pressure regulator unit 37 calculates volumes of the pressure chambers 4, 5 based on the actual position signal 32 and calculates the target mass flow signals 38 taking the calculated volumes into account.

[0073] In the example shown in Figure 1, the first compressed air mass flow 46 flows into the first pressure chamber 4 (and should be regarded as a positive compressed air mass flow 46) and the second compressed air mass flow 47 flows out of the second pressure chamber 5 (and should be regarded as a negative compressed air mass flow 47). In the event that the actual center pressure (i.e., for example, an average value formed from the first actual pressure signal 41 and the second actual pressure signal 42) corresponds to the target center pressure, the center pressure regulator unit 37 generates the two target mass flow signals 38 with the same amount (or weighted according to the respectively assigned piston area of ​​the actuator element 2), whereby, for example, the first target mass flow signal is positive and the second target mass flow signal is negative.If the actual center pressure is less than the target center pressure, the center pressure regulator unit 37 increases the magnitude of the first target mass flow signal and / or decreases the magnitude of the second target mass flow signal. If the actual center pressure is greater than the target center pressure, the center pressure regulator unit 37 decreases the magnitude of the first target mass flow signal and / or increases the magnitude of the second target mass flow signal.

[0074] For example, the center pressure regulator unit 37 initially generates the two target mass flow signals with the amount specified by the mass flow specification signal 36 (preferably weighted according to the respectively assigned piston area of ​​the actuator element 2 and in particular with different signs) and then, as described above, adapts each target mass flow signal for the purpose of pressure control of the center pressure, in particular by the center pressure regulator unit 37 increasing the amount of one of the two target mass flow signals and / or decreasing the amount of the other target mass flow signal.

[0075] By means of the center pressure regulator unit 37 and the control to maintain the condition that the first compressed air mass flow

[0076] 46 is equal to the negative second compressed air mass flow 47 (provided no change in the mean pressure is required), the system behavior can preferably be described by a third-order model. The state adapted within the framework of the control is preferably the differential pressure between the two pressure chambers 4, 5 (or a force acting on the actuator element 2 resulting from the differential pressure) instead of the two absolute pressures of the pressure chambers 4, 5. Preferably, the system does not have zero dynamics. In this way, feedback linearization can be simplified.

[0077] The valve device 8 is designed in particular to control the compressed air mass flows 46,

[0078] 47 such that an integral relationship is established between a compressed air mass flow and a pressure assigned to the pneumatic actuator. For example, an integral relationship is established between the first compressed air mass flow 46 and the first actual pressure signal 41 and / or an integral relationship is established between the second compressed air mass flow 47 and the second actual pressure signal 42. The integral relationship is achieved in particular by the separate adjustment of the compressed air mass flows 46, 47 and the center pressure regulator unit 37.

[0079] The valve device 8 comprises a mass flow control unit 39, which generates control signals 48 based on the target mass flow signals 38. The control signals 48 are, for example, electrical voltages. The control signals 48 can also be referred to as valve control signals.

[0080] The conversion of the target mass flow signals 38 into the control signals 48 is expediently carried out taking into account the actual pressure signals 41, 42. The mass flow control unit 39 expediently does not perform any mass flow control. In particular, the pneumatic system 1 does not have a mass flow sensor for detecting the first compressed air mass flow 46 and / or the second compressed air mass flow 47.

[0081] For example, the mass flow control unit 39 calculates the control signals 48 taking into account a valve characteristic curve and flow function of the respective valve and / or an opening point of the respective valve and / or the air pressure applied to the respective valve. The actual opening point of the valves is continuously determined, for example, by the valve device 8. For example, the actual pressure signals 41, 42, an actual supply pressure signal 52, and / or an actual exhaust air pressure signal 53 are fed to the mass flow control unit, and the mass flow control unit 39 calculates the control signal 48 taking these signals into account. For example, the mass flow control unit 39 calculates the air pressure applied to the respective valve as the pressure ratios of one of the actual pressure signals and the actual supply pressure signal 52 or the actual exhaust air pressure signal 53.

[0082] Optionally, an observed disturbance mass flow can be applied. In this way, an integral behavior between differential pressure and moving mass flow can be achieved. The block designated with the number 40 is to be referred to as actuator device 40. The actuator device 40 is part of the pneumatic system 1 and comprises the valve device and the pneumatic actuator 3. The actuator device 40, in particular the valve device, for example the valves 14, are controlled with the control signals 48. The control signals 48 set in particular the size of the valve opening of the valves 14. The compressed air mass flows 46, 47 flow through the valve openings. By controlling the valve device, the compressed air mass flows 46, 47 are set at the working outputs 9, 10 according to the target mass flow signals 38. The mass flows cause a change in the pressures in the pressure chambers 4, 5 and / or a change in the position of the actuator element 2.

[0083] The first actual pressure signal 41, which is assigned to the first pressure chamber 4, is detected by the first pressure sensor 17, and the second actual pressure signal 42, which is assigned to the second pressure chamber 5, is detected by the second pressure sensor 18. Preferably, the first actual pressure signal 41 describes the air pressure in the first pressure chamber 4, and the second actual pressure signal 42 describes the air pressure in the second pressure chamber 5. The actual position signal 32, which describes in particular the position of the actuator element 2, is detected by the position detection unit 22.

[0084] The control device 19 comprises a differentiator unit 43, which is designed to generate the actual acceleration signal 45 based on a detected position of the actuator element 2. By way of example, the differentiator unit 43 calculates the actual speed signal 44 and / or the actual acceleration signal 45 based on the actual position signal 32. The differentiator unit 43 expediently comprises a filter for providing the actual acceleration signal 45. The bandwidth of the filter is expediently set as a function of a noise behavior of the position detection unit 22 such that a predeterminable noise amplitude in the control signal - for example the control signals 48 - is not exceeded. Preferably, the bandwidth and feedback gains are determined such that a predefined control variable noise is not exceeded.

[0085] In the position control described above, acceleration feedback is preferably used in conjunction with a valve bridge circuit. In particular, the position control described above can achieve a precise positioning of the actuator element 2.

[0086] The control device 19 preferably uses a differential pressure model for position control. In this way, the entire 4th-order nonlinear path can be divided into a 3rd-order model (for the movement of the actuator element 2) and a decoupled 1st-order model (for the center pressure). Three signals (position, velocity, and acceleration) are then fed back for position control.

[0087] Delays can be conveniently taken into account directly in the control design by a linear extension of the linearized system.

[0088] The linearization unit 27 is preferably designed to convert the position controller signal 31 into the mass flow specification signal 36 as part of a linearization, in particular a feedback linearization, so that for the position controller unit 26 a position control loop section of the position control comprising the linearization unit 27 and the pneumatic actuator 3 functions as a linear control system, in particular as a linear control system in which the actuator element 2 is in the middle position.

[0089] The position controller unit 26 experiences the remaining part of the position control loop shown in Figure 2—in particular the position control loop section from the linearization unit 27 to the differentiator unit 43—as a linear position control system. Consequently, the position controller unit 26 can be designed correspondingly simply. In particular, the position control loop section formed from the linearization unit 27, the center pressure controller unit 37, the mass flow control unit 39, the actuator device 40, and the differentiator unit 43 represents a position control system, in particular a linear position control system, for the position controller unit 26.This position control system can be controlled by the position controller unit 26 without the position controller unit 26 having to take into account or taking into account a pressure or a non-linearity of the actuator device 40 (resulting in particular from pneumatic effects).

[0090] Examples of feedback linearizations are described, for example, in J. -J. Slotine and W. Li "Applied Nonlinear Control", Prentice Hall, 1991.

[0091] Preferably, the system is linearized using a disturbance mass flow observer and / or precise zero-point adaptation so that it exactly replicates the fundamental integral behavior. Thus, the system behavior supports the desired accuracy without the need for a higher-level integral behavior (in the position controller unit 26 or in the position controller device 25). This approach is advantageous because the risk of limit cycles can be significantly reduced.

[0092] By precisely adjusting the compressed air mass flow through the valve device, which is particularly designed as a bridge circuit, it is also possible to achieve positions within the resolution of the position detection unit 22 (which is designed, for example, as a position measuring system). For example, a positioning accuracy of ± 0.2 / zm can be achieved.

[0093] As already explained above, an integral relationship between mass flow and pressure is advantageously provided. This can be achieved, in particular, by using a bridge circuit, a zero-point adaptation, a disturbance mass flow observer, and / or the adjustment of compressed air mass flows.

[0094] Furthermore, an integral response from pressure to position is preferably provided. This integral response is maintained in particular by the acceleration feedback. Preferably, the acceleration (and preferably the position) is fed back instead of the pressure. Disturbances such as friction are contained in the acceleration and can therefore be compensated for with the acceleration feedback.

[0095] The aforementioned measures simplify the system behavior, so that a control law with constant feedback gains is sufficient for position control. Figure 3 shows a block diagram of a position control system according to another variant. The position control system shown in Figure 3 is a further development of the position control system shown in Figure 2, so the above explanations also apply (correspondingly) to the position control system shown in Figure 3.

[0096] By way of example, the position controller unit 26 comprises an accuracy controller element 54 which calculates an accuracy controller signal 55 based on the desired position signal 24 and the actual position signal 32 (and optionally further based on the desired speed signal 49 and the actual speed signal 44 and / or the desired acceleration signal 50 and the actual acceleration signal 45).

[0097] The adder 51 calculates the position controller signal 31 based on, in particular as the sum of, the position controller signal 34, the pilot control signal 35, and the precision controller signal 55. In the event that the pilot control element 30 is not present, the adder 51 calculates the position controller signal 31 as the sum of the position controller signal 34 and the precision controller signal 55.

[0098] The accuracy control element 54 serves in particular to achieve a high control accuracy more quickly in the presence of friction, in particular when the actuator element 2 is at a standstill and / or at low speeds. In this way, a high control accuracy can be achieved more quickly.

[0099] Preferably, one or more gain factors are defined in the accuracy controller element 54, using which gain factors the accuracy controller element 54 provides the accuracy controller signal 55. The one or more gain factors are expediently greater than one or more gain factors defined in the position controller element 29 and using which the position controller element 29 calculates the position controller element signal 34. Expediently, all gain factors of the accuracy controller element 54 are greater than each of the gain factors of the position controller element 29. For example, all gain factors of the accuracy controller element 54 are at least 10 times, at least 20 times, at least 50 times, or at least 100 times as large as each of the gain factors of the position controller element 29.

[0100] The accuracy controller element 54 preferably has a limiting device 56 that limits the accuracy controller signal 55. For example, the limiting device 56 limits the accuracy controller signal 55 to a maximum of 20%, a maximum of 10%, or a maximum of 5% of the maximum value of the position controller signal 31.

[0101] Preferably, the gain factors of the accuracy controller element 54 are selected and the limiter device is designed such that, for a first signal value of the position controller element signal 34, the accuracy controller signal 55 is greater than the position controller element signal 34 and, for a second signal value of the position controller element signal 34, the accuracy controller signal 55 is smaller than the position controller element signal 34, the second signal value being greater than the first signal value. In particular, for small deviations between the target signals 24, 49, 50 and the actual signals 32, 44, 45, the accuracy controller signal 55 is dominant over the position controller element signal 34 and can therefore achieve high control accuracy more quickly, particularly at low speeds and / or when the actuator element 2 is at a standstill.

[0102] Optionally, the control device 19 is configured to automatically activate or deactivate the accuracy control element 54. For example, the control device 19 is configured to activate or deactivate the accuracy control element 54 based on the actual speed signal 44. For example, the control device 19 activates the accuracy control element 54 in response to the actual speed signal 44 falling below a predetermined threshold and / or deactivates the accuracy control element 54 in response to the actual speed signal 44 exceeding the predetermined threshold. In particular, the control device 19 activates the accuracy control element 54 at low speeds of the actuator element 2.

[0103] Alternatively or additionally, the activation and / or deactivation of the accuracy control element 54 can be done manually by a corresponding user input.

[0104] Figure 4 shows an exemplary embodiment of the accuracy controller element 54. The accuracy controller element 54 has a first subtraction element 57, which calculates a position deviation signal 58 as the difference between the desired position signal 24 and the actual position signal 32. A first amplification element 59 multiplies the position deviation signal 58 by a first amplification factor to obtain an amplified position deviation signal. A first limiting element 60 (of the limiting device 56) limits the amplified position deviation signal to a predetermined first limiting value and provides the limited, amplified position deviation signal as a first accuracy controller signal component 61. Each accuracy controller signal component can also be referred to as an additional signal component.

[0105] The precision control element 54 has a second amplification element 62, which multiplies the desired speed signal 49 by a second amplification factor to obtain an amplified desired speed signal. A second limiting element 63 limits the amplified desired speed signal to a predetermined second limiting value to obtain a limited, amplified desired speed signal.

[0106] The accuracy control element 54 has a third gain element 64 that multiplies the actual speed signal 44 by a third gain factor to obtain an amplified actual speed signal. A third limiting element 65 limits the amplified actual speed signal to a predetermined third limiting value to obtain a limited, amplified actual speed signal.

[0107] The accuracy controller element 54 has a second subtraction element 66 which calculates a second accuracy controller signal component 67 as the difference between the limited, amplified desired speed signal and the limited, amplified actual speed signal.

[0108] The precision control element 54 has a fourth amplification element 68, which multiplies the desired acceleration signal 50 by a fourth amplification factor to obtain an amplified desired acceleration signal. A fourth limiting element 69 limits the amplified desired acceleration signal to a predetermined fourth limiting value to obtain a limited, amplified desired acceleration signal.

[0109] The precision control element 54 has a fifth amplification element 70, which multiplies the actual acceleration signal 45 by a fifth amplification factor to obtain an amplified actual acceleration signal. A fifth limiting element 71 limits the amplified actual acceleration signal to a predetermined fifth limiting value to obtain a limited, amplified actual acceleration signal.

[0110] The accuracy controller element 54 has a third subtraction element 72 which calculates a third accuracy controller signal component 73 as the difference between the limited, amplified desired acceleration signal and the limited, amplified actual acceleration signal.

[0111] The accuracy controller element 54 has an addition element 74 which adds the first accuracy controller signal component 61, the second accuracy controller signal component 67 and the third accuracy controller signal component 73 to calculate the accuracy controller signal 55.

Claims

Claims 1. Pneumatic system (1) for the position control of an actuator element (2), comprising a pneumatic actuator (3) which comprises the actuator element (2) as well as a first pressure chamber (4) and a second pressure chamber (5), and a valve device (8) which has a first working outlet (9) pneumatically connected to the first pressure chamber (4) and a second working outlet (10) pneumatically connected to the second pressure chamber (5), and is designed to separately adjust respective compressed air mass flows (46, 47) at the working outlets (9, 10) as part of the position control in order to pneumatically actuate the first pressure chamber (4) and the second pressure chamber (5) and thereby position the actuator element (2), wherein the valve device (8) has a position controller device (25) which is designed to to generate a mass flow target signal (36), as well as a center pressure regulator unit (37),which is designed to carry out a pressure control of a mean pressure of the first pressure chamber (4) and second pressure chamber (5) as part of the position control, wherein the position controller device (25) comprises a position controller unit (26) which is designed to generate a position controller signal (31), and a linearization unit (27) which is designed to calculate the mass flow specification signal (36) on the basis of the position controller signal (31), taking into account to generate a non-linear model of the pneumatic actuator (3).

2. Pneumatic system (1) according to claim 1, wherein the position controller signal (31) defines a compressed air mass flow.

3. Pneumatic system (1) according to claim 2, wherein the linearization unit (27) is designed to convert the position controller signal (31) into the mass flow specification signal (36) as part of a linearization, in particular a feedback linearization, so that for the position controller unit (26) a position control loop section of the position control comprising the linearization unit (27) and the pneumatic actuator (3) functions as a linear control system, in particular as a linear control system in which the actuator element (2) is in the center position.

4. Pneumatic system (1) according to any preceding claim, wherein the center pressure regulator unit (37) is designed to calculate target mass flow signals (38) on the basis of the mass flow specification signal (31) as part of the pressure control of the center pressure, wherein the target mass flow signals (38) form the basis of the pneumatic actuation of the pressure chambers (4, 5).

5. Pneumatic system (1) according to any preceding claim, wherein the valve device (8) is designed to adjust the compressed air mass flows (46, 47) as part of the position control such that an integral behavior of a compressed air mass flow (46, 47) to a pressure assigned to the pneumatic actuator (3) is given.

6. Pneumatic system (1) according to any preceding claim, wherein the valve device (8) further comprises a differentiator unit (43) which is designed to generate an actual acceleration signal (45) on the basis of a detected position of the actuator element (2), wherein the position controller device is designed to generate the mass flow specification signal (36) taking into account the actual acceleration signal (45).

7. Pneumatic system (1) according to claim 6, wherein due to the consideration of the actual acceleration signal (45) an integral behavior of a / the pressure assigned to the pneumatic actuator (3) to the position of the actuator member (2) is given.

8. Pneumatic system (1) according to any preceding claim, wherein the position controller device (25) is designed to provide a / the position controller signal (31) underlying the mass flow specification signal (36) without an I component.

9. Pneumatic system (1) according to one of the preceding claims, wherein the valve device (8) comprises a first valve unit providing the first working output (9) and a second valve unit providing the second working output (10), wherein the first valve unit and the second valve unit each function as 3 / 3-way valves.

10. Pneumatic system (1) according to any preceding claim, wherein the valve device (8) comprises a bridge circuit of four 2 / 2-way valves providing the two working outputs (9, 10).

11. Pneumatic system (1) according to any preceding claim, wherein the position controller device (25) is designed to generate the position controller signal (31) without taking into account an actual pressure signal (41, 42) related to the pneumatic actuator (3).

12. Pneumatic system (1) according to one of the preceding claims, wherein the position controller device (25) comprises a / the position controller unit (26) which is designed to calculate a / the position controller signal (31), on the basis of which the position controller device (25) calculates the mass flow specification signal (36), wherein the position controller unit (26) comprises a position controller element (29) for calculating a position controller element signal (34) and an accuracy controller element (54) for calculating an accuracy controller signal (55), and is designed to calculate the position controller signal (31) on the basis of the position controller element signal (34) and the accuracy controller signal (55).

13. Pneumatic system (1) according to claim 12, wherein the position controller element (29) has one or more gain factors for calculating the position controller element signal (34) and the accuracy controller element (54) has one or more gain factors for calculating the accuracy controller signal (55), wherein each gain factor of the accuracy controller element (54) is greater than each gain factor of the position controller element (29).

14. Pneumatic system (1) according to claim 12 or 13, wherein the accuracy regulator element (54) has a limiting device (56) for limiting the accuracy regulator signal (55).

15. Method for controlling the position of an actuator element (2) of a pneumatic actuator (3) comprising a first pressure chamber (4) and a second pressure chamber (5), wherein a valve device (8) having a first working outlet (9) pneumatically connected to the first pressure chamber (4) and a second working outlet (10) pneumatically connected to the second pressure chamber (5), separately adjusts respective compressed air mass flows (46, 47) at the working outlets (9, 10) as part of the position control in order to pneumatically actuate the first pressure chamber (4) and the second pressure chamber (5) and thereby position the actuator element (2), wherein the valve device (8) has a position controller device (25) which generates a mass flow preset signal (36) underlying the compressed air mass flows (46, 47), and a center pressure controller unit (37) ,which, as part of the position control, carries out a pressure control of a mean pressure of the first pressure chamber (4) and second pressure chamber (5).

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