PNEUMATIC LINEARACTOR

Description

TECHNICAL AREA

[0001] The present invention relates to the field of pneumatic actuators, in particular a cost-effective design of a device that can replace double-acting pneumatic cylinders in certain applications. BACKGROUND

[0002] For the state of the art, reference is made to publications CN 102 979 781 A, EP 0 786 599 A2, and US 2021 / 010492 A1.

[0003] There are various types of pneumatic actuators. Pneumatic cylinders, in particular, are used in a wide variety of applications. Pneumatic actuators are also commonly used for force control, for example, in automated, robot-assisted surface processing or more generally in applications where a robot, for instance, needs to touch a surface "gently" (without impact) with a tool. An example of a pneumatic handling device ( handling deviceThe application of such a device to industrial robots is described in US 10,906,177. Known devices and systems include, among other things, bellows cylinders, air muscles, or double-acting pneumatic cylinders, which makes such devices complex and expensive to manufacture. One requirement for such a handling device for robot-assisted surface processing is the ability to absorb bending moments.

[0004] The inventor set himself the task of creating a cost-effective pneumatic linear actuator that is particularly suitable for applications in the field of robot-assisted surface processing. SUMMARY

[0005] The aforementioned problem is solved by the device according to claim 1. Various embodiments and further developments are the subject of the dependent claims.

[0006] A device is described. According to one embodiment, the device comprises the following: a first housing with a first pressure chamber; a first rod inserted from the outside into the first pressure chamber of the first housing; a first mounting plate and a second mounting plate, wherein the first mounting plate is rigidly connected to the first rod and wherein the second mounting plate is rigidly connected to the first housing; a first rod seal arranged around the first rod, which seals the first pressure chamber; and a first rod guide mounted on the first housing, which is configured to guide the first rod along its longitudinal axis. No piston is arranged in the pressure chamber.Rather, an unsealed annular gap exists inside the first pressure chamber between the first rod and an inner wall of the first pressure chamber, allowing any gas pressure present in the first pressure chamber to propagate throughout the entire first pressure chamber up to the first rod seal. The device further comprises a restoring element arranged to counteract a force exerted on the first rod by the gas pressure, the restoring element being located outside the first housing between the first mounting plate and the second mounting plate, and configured to generate an attractive force between the first mounting plate and the second mounting plate.

[0007] Further embodiments relate to handling devices or linear actuators with one or more of the aforementioned devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various implementations are explained in more detail below using the examples shown in the figures. The illustrations are not necessarily to scale, and the invention is not limited to the aspects shown. Rather, emphasis is placed on illustrating the principles underlying the depicted embodiments. Figure 1 is an exemplary schematic representation of a robot-assisted grinding device with a grinding machine, which is coupled to an industrial robot by means of a force-controlled linear actuator; the linear actuator causes a partial mechanical decoupling of the industrial robot and the grinding machine. Figure 2 illustrates an example of a pneumatic linear actuator (handling device ( handling device ) in a side view. Figure 3 is a schematic longitudinal section representation of a first embodiment. Figure 4is a schematic longitudinal section view of a second embodiment. Figure 5 is a schematic longitudinal section representation of a third embodiment at medium deflection. Figure 6 illustrates the example from Fig. 5 with minimal deflection. DETAILED DESCRIPTION

[0009] In robot-assisted surface processing, a machine tool (e.g., a grinding machine, a drilling machine, a milling machine, a polishing machine, etc.) is guided by a manipulator, for example, an industrial robot. The machine tool can be guided in various ways by the so-called end effector flange, the position of which determines the TCP ( Tool Center PointThe manipulator is coupled to the TCP; the manipulator can typically adjust the position and orientation of the TCP virtually arbitrarily to move a machine tool along a trajectory, e.g., parallel to the surface of a workpiece. Industrial robots are usually position-controlled, which allows for precise movement of the TCP along the desired trajectory. However, the following applies not only to robot-assisted surface finishing but also to robotics applications in general, where a robot with a tool needs to contact a surface more or less gently (without impact). This can also occur, for example, on Pick and Place -Applications apply.

[0010] In many applications, process force control (e.g., force when contacting a workpiece or contact force during surface processing such as grinding force) is necessary, which is often difficult to achieve with sufficient accuracy using conventional industrial robots. The large and heavy arm segments of an industrial robot possess too great a moment of inertia for a controller ( closed-loop controllerThe manipulator could react quickly enough to fluctuations in the process force. To solve this problem, a smaller (and lighter) linear actuator, compared to an industrial robot, can be positioned between the manipulator's end-effector flange and the machine tool. This actuator couples the manipulator's end-effector flange to the machine tool. During surface machining, the linear actuator only regulates the process force (i.e., the contact force between the tool and the workpiece), while the manipulator moves the tool or the machine tool, including the linear actuator, along the desired trajectory in a position-controlled manner. Through force control, the linear actuator can compensate for inaccuracies in the position and shape of the workpiece being machined, as well as inaccuracies in the manipulator's trajectory (within certain limits).Nevertheless, there are robots that are able to adjust the process force using force / torque control even without the aforementioned linear actuator, although this is comparatively complex and expensive.

[0011] Before various embodiments are explained in detail, a general example of a robot-assisted grinding device will first be described. It should be understood that the concepts described here are also transferable to other types of surface processing (e.g., polishing, milling, drilling, etc.) and are not limited to grinding. As mentioned, the embodiments described here can be used as linear actuators (handling devices) in a wide variety of applications and generally represent a cost-effective alternative to linear actuators driven by pneumatic cylinders.

[0012] According to Fig. 1A robot-assisted grinding device comprises a manipulator 80, for example an industrial robot, and a grinding machine 50 with a rotating grinding tool 51, wherein the grinding machine 50 can be coupled to the end-effector flange of the manipulator 1 via a linear actuator 20. The position and orientation of the end-effector flange also defines the TCP (Cyclical Point Combination). Strictly speaking, the TCP is not a point, but a vector and can be described, for example, by three spatial coordinates (position) and three angles (orientation). In robotics, generalized coordinates (usually six joint angles of the robot) in configuration space are sometimes used to describe the position of the TCP. The position and orientation of the TCP are sometimes also referred to as "pose". The position (including orientation) of the TCP as a function of time defines the movement of the grinding tool, which is called the trajectory.The TCP (Tool Center Point) is often defined as the center point of the robot's end effector flange, but this is not necessarily the case. The TCP can be any point (and theoretically even located outside the robot) whose position and orientation can be set by the robot. The TCP can also define the origin of the tool coordinate system.

[0013] In the case of an industrial robot with six degrees of freedom, the manipulator 80 can be constructed from four segments 82, 83, 84, and 85, each connected by joints G11, G12, and G13, respectively. The first segment, 82, is usually rigidly connected to a base 81 (although this is not necessarily the case). Joint G11 connects segments 82 and 83. Joint G11 can be two-axis, allowing rotation of segment 83 about a horizontal axis (elevation angle) and a vertical axis (azimuth angle). Joint G 12 connects segments 83 and 84 and allows segment 84 to pivot relative to the position of segment 83. Joint G 13 connects segments 84 and 85. Joint G 13 can be biaxial and therefore (similar to joint G 11) allow pivoting in two directions.The end effector flange, and thus also the TCP, has a fixed relative position to segment 85, which usually also includes a pivot joint (not shown) that allows a rotational movement of the end effector flange 86 arranged on segment 85 about a longitudinal axis A of segment 85 (in . Fig. 1 The line drawn as a dashed line (in the example shown also corresponds to the axis of rotation of the grinding tool) represents the axis of rotation of the grinding tool. Each axis of a joint is assigned an actuator (e.g., an electric motor) that can effect a rotational movement around the respective joint axis. The actuators in the joints are controlled by a robot controller 70 according to a robot program. Various industrial robots / manipulators and their associated controllers are well-known and are therefore not discussed further here.

[0014] The Manipulator 80 is typically position-controlled, meaning the robot controller can define the pose (location and orientation) of the TCP and move it along a predefined trajectory. Fig. 1The longitudinal axis of segment 85, on which the TCP is located, is labeled A. When the actuator 100 rests against an end stop, the position of the end effector flange (or the TCP) also defines the position of the grinding machine 50 (and also of the tool / grinding wheel 51). As mentioned earlier, the linear actuator 100 serves to adjust the contact force (process force) between the tool and the workpiece 60 to a desired value during the grinding process. Direct force control by the manipulator 80 is generally too imprecise for grinding applications because the high inertia of segments 83 to 85 of the manipulator 80 makes rapid compensation of force peaks (e.g., when the grinding tool touches the workpiece 60) practically impossible with conventional manipulators.For this reason, the robot controller 70 is designed to control the pose (position and orientation) of the TCP of the manipulator 80, while force control is usually accomplished exclusively with the help of the actuator 100.

[0015] As mentioned previously, during the grinding process, the contact force FK between the grinding tool (grinding machine 50 with grinding wheel 51) and the workpiece 60 can be adjusted using the linear actuator 100 and a force control system (which, for example, can be implemented in the controller 70) so that the contact force FK (in the direction of the longitudinal axis A) between the grinding wheel 51 and the workpiece 60 corresponds to a predefined target value. The contact force FK is a reaction to the actuator force FA, with which the linear actuator 100 presses against the workpiece surface. If there is no contact between the workpiece 60 and the tool 51, the actuator 100 moves against an end stop (not shown, as it is integrated into the actuator 100) due to the lack of contact force on the workpiece 60 and presses against it with a defined force. The force control system can be continuously active during this process.In this situation (no contact), the actuator deflection is therefore at its maximum, and actuator 100 is in an end position. The defined force with which actuator 100 presses against the end stop can be very small or (theoretically) even reduced to zero to ensure the gentlest possible contact with the workpiece surface.

[0016] The position control of the manipulator 80 can operate completely independently of the force control of the actuator 100 (which can also be implemented in the controller 70). The actuator 100 is not responsible for positioning the grinding machine 50, but only for setting and maintaining the desired contact force FK during the grinding process and for detecting contact between the tool 51 and the workpiece 60. Contact can be easily detected, for example, by the actuator moving out of its end position (the actuator deflection is less than the maximum deflection at the end stop).

[0017] It is understood that the direction of action of the actuator 90 and the axis of rotation of the grinding machine 50 do not necessarily have to coincide with the longitudinal axis A of segment 85 of the manipulator 80. In the case of a pneumatic actuator, force control can be implemented in a manner known per se using a control valve, a controller (e.g., implemented in the control unit 70), and a compressed air reservoir or compressor. Since the inclination to the vertical is relevant for taking gravity (i.e., the weight of the grinding machine 50) into account, the actuator 100 can include an inclination sensor, or this information can be determined based on the joint angles of the manipulator 80. The determined inclination is taken into account by the force controller. The specific implementation of the force control is known per se and is not important for further explanation; therefore, it will not be described in more detail.The linear actuator 100 not only enables a certain mechanical decoupling between manipulator 80 and workpiece 60, but is also able to compensate for inaccuracies in the positioning of the TCP and / or the workpiece.

[0018] In another type of robot-assisted surface finishing, the machine tool is mounted to a stationary base via a linear actuator, while a conventional industrial robot positions a workpiece and moves it towards the machine tool (e.g., a grinding machine). The linear actuator also controls the process force, while the robot's position can be controlled in the conventional manner. This means that during the surface finishing process, the linear actuator (supported by the base) pushes the machine tool against the workpiece, which is held in a defined position by the robot.

[0019] The linear actuator 100 is also referred to below as a handling device ( handling apparatus ) designated. Fig. 2 illustrates an exemplary embodiment in a side view. The device has, according to Fig. 2 two opposing mounting plates 101 and 102 (mounting flanges), wherein the first mounting plate 101 is designed to mechanically couple the device to a tool (e.g. a gripper) or a machine tool (e.g. a grinding machine, a polishing machine, etc.), and wherein the second mounting plate 102 is designed to mechanically couple the device to the end effector flange 86 of a manipulator (see Fig. 1 ) to couple. For example, the second mounting plate 102 is mounted to the end effector flange 86 using screws. Similarly, the machine tool can be mounted to the first mounting plate 101 using screws. Alternative mounting options (clamps, bayonet fittings, etc.) are possible.

[0020] In the illustrated example, the interior of the handling device located between the mounting plates 101, 102 is covered by a bellows 105. This bellows serves primarily to keep dust and other contaminants away from the internal components of the device. Other cover designs are also possible.

[0021] Fig. 3 Figure 1 illustrates a first example of the handling device described here by means of a schematic sketch. It should be emphasized beforehand that this is not a conventional combination of piston and (pneumatic) cylinder, but merely one in a rod guide 112 ( rod guidance ) guided rod 110 ( rod ), which is inserted into an interior of a housing 130. An ordinary rod seal 113 ( rod sealThe rod seal 113 seals the interior of the housing 130 along the circumference of the rod 110. That is, the rod seal 113 and the rod guide 112 are axially spaced apart (along the longitudinal axis B of the rod). The rod 110 is slidably mounted in the rod guide 112 along its longitudinal axis. In the illustrated example, the rod guide 112 is arranged in a bushing 131 located in the housing 130. For example, the rod guide 112 can be pressed into the bushing 131. Other techniques for fastening the rod guide 112 in or to the housing 130 are possible. The rod guide 112 can be a recirculating ball bearing or incorporate one. The rod guide is usually made of stainless steel. Various rod guides are known and commercially available and are therefore not discussed further here.

[0022] The rod guide 112 allows movement of the rod 110 only in the longitudinal direction (along the longitudinal axis B) and can, in particular, absorb bending moments, i.e., torques about an axis normal / perpendicular to the longitudinal axis B. Rod guides are also referred to as shaft guides, and especially as linear bearings. In one embodiment, a linear ball bearing is used as the rod guide. Linear ball bearings are also referred to as ball bushings and have the advantage that they cause comparatively low (practically no) static friction between the bearing and the rod, thus largely avoiding a stick-slip effect.

[0023] When the rod 110 is moved, the volume of the interior of the housing 130 changes. The interior of the housing can be supplied with compressed air (see Fig. 3(Inlet / outlet 115 for compressed air), which is why the interior is also referred to as pressure chamber 114 (pressure p 1). The end face of the rod 110, located outside the housing 130, is connected to one of the mounting plates (in the illustrated example, to the mounting plate / flange 101). The housing 130 is mounted on the other mounting plate (in the illustrated example, to the mounting plate / flange 102). The mechanical connections between the rod 110 and the mounting plate 101, as well as between the housing 130 and the mounting plate 102, can be made, for example, by means of screws. However, other connection techniques are also possible (e.g., gluing, press fits, etc.).

[0024] At an (air) pressure p 1 in the pressure chamber 114, the force F 1 acting on the rod 110 (along its longitudinal axis B) is equal to p 1 ·A 1 , where A 1 =d 1 2< π / 4. The pressure p1 is generally an overpressure, i.e., greater than the atmospheric pressure outside the pressure chamber. The parameter d1 denotes the diameter of the rod 110 in the pressure chamber 114, specifically the diameter of the rod 110 in the region of the rod seal 113. In the examples discussed here, the pressure chamber 114 has the shape of a cylinder with an inner diameter d1', with an (annular) gap δ between the circumference of the rod 110 and the inner wall of the pressure chamber 114 (i.e., d1' = d1 + 2δ). The force F1 exerted by the compressed air pushes the two mounting plates 101 and 102 apart against the action of a restoring force FR, which can be generated, for example, by a spring 150. In the example shown, the spring 150 also acts between the two mounting plates 101 and 102 and causes a displacement ΔL (see Fig. 2The restoring force FR of the rod 110 depends on the spring constant (FR ≈k·ΔL, where k is the spring constant). The minimum distance between the mounting plates 101 and 102, defined, for example, by an end stop, is L 0 (ΔL=0, see Fig. 2 The maximum distance between mounting plates 101 and 102 can also be determined by an end stop. The end stops are in Fig. 3 Not shown. Other return elements can be used instead of spring 150.

[0025] Unlike a conventional piston / cylinder combination, the pneumatically effective area is equal to the cross-sectional area of ​​the rod 110 in the region of the rod seal 113. In the example shown, there is also no equivalent to a piston seal (which would move with the piston), but only the rod seal 113 mounted in the housing 130 (and not moving with the rod). Since there is no piston with a piston seal in the examples described here, the gas pressure p1 present inside the housing 130 can propagate throughout the entire pressure chamber 114 (i.e., also into the annular gap δ) up to the rod seal 113. In contrast, a piston would divide the interior of the housing 130 into two pressure chambers, which is not the case in the examples described here. The housing 130 contains only one (single) pressure chamber 114.At the same time, the rod guide 112 (linear bearing) ensures reliable absorption of bending moments in a compact and cost-effective design. In conventional actuators that use standard pneumatic cylinders, the linear guides that can absorb significant bending moments are arranged separately next to the pneumatic cylinder (i.e., parallel to it).

[0026] The housing 130 can be made of plastic, for example, using injection molding or additive manufacturing (3D printing). The material from which the housing 130 is made is more elastic (less rigid) than the material of the rod guide (usually steel). In another example, the housing 130 is manufactured using aluminum die casting. Machining (e.g., by milling) is only necessary in the area of ​​the bushing 131 and, if necessary, on the surface that is connected to the mounting plate 102. Overall, the linear actuator is designed according to Fig. 3 It is essentially simpler and cheaper to manufacture than a linear actuator that uses a conventional pneumatic cylinder as the actuating element.

[0027] In the Fig. 4 The example shown depicts a further arrangement with a rod 120, a housing 140, a rod guide 122, and a rod seal 123. The left part in Fig. 4 It is structured the same as in the example from Fig. 3 and reference is made to the description above. The right part of the device in Fig. 4 is constructed analogously to the left part, but in reverse ( upside-down ) connected to the mounting plates 101, 102. The two actuating elements with longitudinal axes B and B' (each comprising a housing with rod guide and rod seal and a rod) are arranged, so to speak, antiparallel to each other.

[0028] The illustrated arrangement with two rods is more stable with regard to absorbing bending moments and can generate higher forces. The two adjusting elements can also be arranged parallel (instead of antiparallel). In this case, the right part of the device would be in Fig. 4 Constructed in the same way as the left part and connected to the mounting plates 101, 102 in the same manner. In some embodiments, more than two combinations of housing with pressure chamber, rod and rod guide are provided in order to increase the maximum actuator force (at the same pressure in the pressure chambers, the pneumatically effective end faces of the rods add up) and to increase the maximum possible bending moments.

[0029] The housing 140 of the second actuator is connected to the mounting plate 101 (e.g., by means of screws), and the end face of the rod 120, located outside the housing 140, is connected to the opposite mounting plate 102 (e.g., also by means of a screw). The housing 140 has a bushing 141 in which the rod guide 122 is arranged. The rod seal 123 is arranged (at an axial distance) adjacent to the rod guide 122 in the housing 140 (analogous to the housing 130 and the rod seal 113). The interior of the housing 140 forms a pressure chamber 124, the volume of which depends on the position of the rod 120. Compressed air (pressure p₂) can enter the pressure chamber 124 via the inlet / outlet 125. The force F 2 acting on the rod 120 is proportional to the pressure p 2 and to the pneumatically effective area A 2 =d 2 2< π / 4 (i.e. F 2 =p 2 ·A 2 ).

[0030] In the example from Fig. 4The combination of the second rod 120 and the second pressure chamber 124 arranged in the second housing 140 can function as a restoring element if the gas pressure p₂ in the second pressure chamber 124 is a vacuum. A vacuum is defined as a pressure p₂ that is lower than the atmospheric pressure outside the device. A pressure chamber pressurized with a vacuum causes the respective rod / housing / pressure chamber combination to behave practically like a spring, generating a restoring force. In this case, the force is regulated by adjusting the (over)pressure in the other pressure chamber, since overpressure is easier to control in practice than underpressure.

[0031] As already mentioned in relation to Fig. 3In this example, the pneumatically effective areas A1 and A2 are also mentioned, corresponding to the cross-sectional areas of the rods 110 and 120 in the area of ​​the rod seals 113 and 123. Areas A1 and A2 can be identical. Piston seals are not required, unlike in conventional solutions. The rod seals 113 and 123 are arranged in the respective housings 130 and 140 and are not movable relative to these housings. A spring is not necessary in this example because the restoring force F2 is generated pneumatically. Nevertheless, a spring can be added (similar to the one in...). Fig. 3 ) are planned.

[0032] As mentioned, housings 130 and 140 can be made of a more elastic (less rigid) material than the material used for rod guides 112 and 122 (usually steel). For example, housings 130 and 140 are made of plastic (injection molding) or aluminum (die casting). As mentioned, additive manufacturing processes (3D printing) are also possible. The relatively more elastic housing allows deviations from perfect parallelism of the longitudinal axes B and B' of rods 110 and 120, respectively, to be compensated for (within certain limits) and prevents the linear actuator from jamming. Deviations from parallel alignment of the longitudinal axes B and B' can arise due to manufacturing tolerances and also due to bending moments during operation.

[0033] Fig. 5 illustrates another embodiment, which is similar to the example from Fig. 4is very similar. In terms of function, the embodiment corresponds to that shown in Fig. 5 essentially the example from Fig. 4 , wherein two antiparallel actuating elements are arranged between the mounting plates 101 and 102. Additionally, a spring 150 is arranged between the two mounting plates 101, 102 as a return element, which brings the linear actuator / handling device into a defined end position, even if the pressure chambers 114 and 124 of the two actuating elements are not pressurized.

[0034] Housings 130 and 140, as in the previous example, have bushings 131 and 141, respectively, for the rod guides 112 and 122. Rod seals 113 and 123 are arranged coaxially with the rod guides 112 and 122 in the respective housings. The two rods 110 and 120 are guided antiparallel within the rod guides 112 and 122. Depending on the rod position (i.e., depending on the deflection ΔL of the linear actuator), the volume of the pressure chambers 114 and 124 in the housing varies. In the Fig. 5 In the depicted situation, the deflection ΔL is in a medium range. The maximum volume of the pressure chambers 114 and 124 is defined by an end stop (not shown). The rod 110 is rigidly connected to the mounting plate 101 by means of the screw 111. Similarly, the rod 120 is connected to the mounting plate 102 by means of the screw 121. The associated housings 130 and 140 are rigidly connected (e.g., screwed) to the respective other mounting plate.

[0035] In the retracted state (i.e., at minimum deflection ΔL=0), the end faces of the rods 110 and 120 located inside the pressure chambers 114, 124 must not be in complete contact with the wall of the pressure chamber, as otherwise no surfaces A1 and A2 would be available on which the pressure could act and exert a corresponding force p1 A1 or p2 A2. The in Fig. 5The screw 129, shown, which is screwed into the end face of the rod 120, forms an end stop for the retracted state. The screw 129 protrudes from the end face of the rod 110 and thus also forms a spacer, so that at least part of the cross-sectional area A2 remains pneumatically effective and a force can be exerted on the rod even in the fully retracted state due to the pressure p2 in the pressure chamber 124. Due to the mechanical coupling of the two rods 110, 120 and the associated housings 130, 140 with the mounting plates 101, 102, a spacer on the rod 110 is not strictly necessary.

[0036] A permanent magnet 118, which is part of a magnetic displacement sensor ( ), can be attached to the other rod (left rod 110) with a screw 119. displacement sensor in Fig. 5 and 6(not shown). The displacement sensor is designed to measure the deflection ΔL of the linear actuator. Various types of suitable magnetic and other displacement sensors are known and are therefore not discussed further. Relevant for the example shown is the magnet 118, mounted on the rod 110 and moving with it, which enables a simple displacement measurement.

[0037] Fig. 6 The device shows Fig. 5In a fully retracted state (ΔL=0), the screw head of screw 129 can be seen forming an end stop and resting against the wall of the pressure chamber 124 (opposite the end face of rod 120). Only the screw head of screw 129 rests against the wall of the pressure chamber 124; the end face of rod 120 does not. In the illustrated position (ΔL=0), the end face of rod 120 is spaced a distance x from the opposite wall of the pressure chamber 124. It is understood that screw 129 can also be screwed into the opposite wall surface of the pressure chamber 124 instead of the end face of rod 120. Alternatively, a spacer can be directly molded onto the housing wall or the rod. The spacer and housing 140 can be a single component (e.g., a casting).

Claims

1. A device, having: a first housing (130) having a first pressure chamber (114); a first rod (110) inserted from the outside into the first pressure chamber (114) of the first housing (130); a first rod seal (113) arranged around the first rod (110) and sealing the first pressure chamber (114), wherein, in the interior of the first pressure chamber (114), there is an unsealed annular gap (δ) between the first rod and an inner wall of the first pressure chamber (114), so that a gas pressure (p1) present in the first pressure chamber (114) can spread throughout the entire first pressure chamber (114) up to the first rod seal (113); a first rod guide (112) mounted on the first housing (130) and configured to guide the first rod (110) along its longitudinal axis; and a return element (150) which is arranged so that it can counteract a force caused by the gas pressure (p1) on the first rod (110), characterized in that the device has a first mounting plate (101) and a second mounting plate (102), wherein the first mounting plate (101) is fixedly connected to the first rod (110) and wherein the second mounting plate (102) is fixedly connected to the first housing (130), and that the return element is arranged outside the first housing (130) between the first mounting plate (101) and the second mounting plate (102), wherein the return element is designed to generate an attractive force (FR, F2) between the first mounting plate (101) and the second mounting plate (102).

2. The device according to claim 1, wherein the first housing (130) has a single pressure chamber (114) and wherein substantially the same pressure prevails throughout the entire first pressure chamber.

3. The device according to claim 1 or 2, wherein the first housing (130) has a bushing (131) outside the pressure chamber (114) and the first rod guide (112) is arranged in the bushing (131).

4. The device according to any one of claims 1 to 3, wherein the first rod seal (113) is arranged in a groove of the first housing (130) which extends around the first rod (110).

5. The device according to any one of claim 1 to 4, further having: a second housing (140) having a second pressure chamber (124), the second housing (140) being fixedly connected to the first mounting plate (101); a second rod (120) inserted from the outside into the second pressure chamber (124) of the second housing (140) and fixedly connected to the second mounting plate (102); a second rod seal (123) arranged around the second rod (110) and sealing the second pressure chamber (124), wherein, in the interior of the second pressure chamber (124), there is an unsealed annular gap (δ) between the second rod (120) and an inner wall of the second pressure chamber (124), so that a gas pressure (p2) present in the second pressure chamber (124) can spread throughout the entire second pressure chamber (124) up to the second rod seal (123); a second rod guide (122) mounted on the second housing (140) and configured to guide the second rod (120) along its longitudinal axis (B').

6. The device according to any one of claims 1 to 5, wherein the return element is a spring (150).

7. The device according to claim 5, wherein the return element is formed by the combination of the second pressure chamber (124) and the second rod (120), wherein the gas pressure (p2) present in the second pressure chamber (124) is a negative pressure.

8. The device according to any one of claim 1 to 7, further having: a spacer (129) serving as an end stop and arranged either on an end face of the first rod (110) located in the first pressure chamber (114) or on a wall of the second pressure chamber (124) opposite the end face of the first rod (110), and wherein the spacer (29) ensures a distance (x) between the end face of the first rod (110) and the opposite wall of the first pressure chamber (114) in a retracted end position of the device.

9. The device according to claim 8, wherein the spacer (129) is screwed into the first rod (110) or the first housing (130), or wherein the spacer (129) is an integral part of the first housing (130) or the first rod (110).

10. The device according to any one of claims 1 to 9, wherein the first housing (130) is made of a material that is more elastic than the material from which the first rod (110) is made.

11. The device according to any one of claims 1 to 10, wherein the device functions as a pneumatic linear actuator, and wherein the first rod guide (112) is designed to absorb bending moments.

12. The device according to claim 11, wherein the first rod guide (112) is a linear bearing, in particular a linear ball bearing or a ball bushing.

13. The device according to any one of claims 11 or 12, wherein the first rod guide (112) is arranged in a bushing of the housing (130) outside the pressure chamber and spaced from the rod seal (113).

14. A system, comprising: a manipulator; a device according to any one of claims 1 to 10 mounted on an end effector flange of the manipulator, and a tool mounted on the device or machine tool mounted on the device.

15. A system, comprising: a manipulator for holding and positioning a workpiece; a base-mounted device according to any one of claims 1 to 10, and a tool mounted on the device or machine tool mounted on the device.