Pneumatic actuator and portable tool

Abstract

A pneumatic actuator (240), comprising: a pressure reducer (270) for delivering gas under a reduced pressure to a control valve; the control valve (280) selectively supplying gas to a pneumatic cylinder (290) or discharging gas from the cylinder (290) to the environment; a replaceable gas capsule (260) for supplying the gas under increased pressure; where the actuator has a first mode of operation for moving the piston (293) to the extended position, and has a second mode of operation for retracting the piston (293). A method for assembling a pneumatic actuator. A portable tool, a clamping device, a screw clamp comprising such a pneumatic actuator. A method for assembling the screw clamp. A method for repairing the screw clamp.

Claims

1. A pneumatic actuator, comprising: a replaceable gas capsule with a capsule outlet, for supplying a gas under elevated pressure; a pressure reducer connected with an outlet of the gas capsule, adapted for providing gas under a reduced pressure; a control valve connected with an outlet of the pressure reducer for receiving the gas under reduced pressure, having a first outlet for selectively supplying the gas to a pneumatic cylinder, and having a second outlet for selectively discharging the gas from the cylinder into the environment; the pneumatic cylinder with a piston that is movable from a retracted position to an extended position.

2. The pneumatic actuator of claim 1, wherein the pressure reducer is an adjustable pressure reducer, and the adjustable pressure reducer has an adjustment knob for setting a pressure at the outlet of the pressure reducer.

3. The pneumatic actuator of claim 1, wherein the pneumatic cylinder comprises: a cylinder wall with an internal diameter from 30 to 60 mm; and a piston that is axially movable with respect to the cylinder wall.

4. The pneumatic actuator of claim 1, wherein: the pneumatic cylinder is a single-acting pneumatic cylinder; and the pneumatic actuator further comprises a spring for at least partially pushing back the piston.

5. The pneumatic actuator of claim 1, wherein: the outlet of the gas capsule is fluidly connected with the inlet of the pressure reducer via a transition element; the pressure reducer has an internal screw thread for attaching the transition element, and where the transition element comprises a corresponding external screw thread; and the transition element further comprises an internal screw thread for attaching the gas capsule, and where the gas capsule comprises a corresponding external screw thread; and the transition element further comprises a puncture element for puncturing a portion of the gas capsule when mounting the gas capsule in the transition element, where the puncture element is fluidly connected with the inlet of the pressure reducer.

6. The pneumatic actuator of claim 1, wherein the gas capsule is surrounded by a cylinder-shaped metal casing of at least 1.5 mm thickness and an external diameter from 45 mm to 65 mm.

7. The pneumatic actuator of claim 1, wherein the gas capsule is surrounded by a thermal insulation provided within the aluminium casing.

8. The pneumatic actuator of claim 1, wherein: the control valve has an internal space that is in fluid connection with the first outlet of the control valve; and the control valve further comprises one single slidable control pin to connect the internal space with either the inlet of the control valve corresponding to a first mode of operation, or with the second outlet of the control valve corresponding to a second mode of operation.

9. The pneumatic actuator of claim 1, wherein: the control valve comprises a first depressible control pin for connecting the inlet of the control valve and the first outlet of the control valve, and a first spring for pushing back the first control pin to a position where the first outlet is closed off from the inlet; the control valve further comprises a second depressible control pin for connecting the first outlet and the second outlet of the control valve, and a second spring to push back the second control pin to a position where the first outlet is closed off from the second outlet; the first mode of operation corresponds to the first control pin being in the depressed position and the second control pin in pushed-back position; and the second mode of operation corresponds to the second control pin being in the depressed position and the first control pin in the pushed-back position.

10. The pneumatic actuator of claim 1, wherein the actuator is implemented such that for each activation and deactivation less than 25 mL gas from the gas capsule is used.

11. The pneumatic actuator of claim 1, wherein the pneumatic actuator without gas capsule has a mass of less than 700 grams.

12. A portable clamping device comprising: a pneumatic actuator according to claim 1; a first arm forming part of a guide profile or to which a guide profile is connected, where the guide profile has a linear portion; and a second arm movably attached to the linear portion of the guide profile, the second arm having two through-openings, wherein: the first arm and the second arm extend substantially perpendicular with respect to the linear portion of the guide profile; and the pneumatic actuator is connected with the second arm and extends in a direction substantially parallel to the linear portion of the guide profile for clamping one or more workpieces.

13. The portable clamping device of claim 12, wherein the first arm has a first contact surface, and the pneumatic actuator has a second contact surface for clamping the one or more workpieces between the first and second contact surface.

14. The portable clamping device of claim 12, wherein the mass of the clamping device is less than 2600 grams.

15. The portable clamping device of claim 12, wherein the clamping device further comprises a safety bolt to block the piston.

16. A method for repairing a clamping device, the method comprising: providing a clamping device according to claim 12; removing the gas capsule, if present; removing the hardened transition element; and screwing in a new hardened transition element.

17. A method for assembling a clamping device, the method comprising: providing a pneumatic actuator according to claim 1; providing a guide profile having a linear portion comprising a first arm forming part of the guide profile or, alternatively, providing a guide profile having a linear portion, then connecting a first arm to the guide profile; providing a second arm having a first opening and a second opening; connecting the pneumatic actuator to the first opening of the second arm; and inserting the guide profile through the second opening of the second arm.

18. The method of claim 17, further comprising connecting a top unit to the piston or to an extension of the piston.

19. A method for assembling a pneumatic actuator, the method comprising: providing a body comprising a pressure reducer and a control valve; inserting at least one control pin, and at least one ball or first element having a collar, and at least one spring in an opening of the body; sealing the opening at the side of the spring; screwing in a hardened transition element in the body; and heating a first aluminium casing, and applying the first aluminium casing in heated state around the body, and crimping the first aluminium casing.

20. The method of claim 19, further comprising: applying a second metal casing against the body, for surrounding the space configured for containing the gas capsule.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Referring specifically to the figures, it is emphasized that the particulars shown serve only as an example and only for the illustrative discussion of the various embodiments of the present invention. They are represented with the aim of supplying what is considered to be the most useful and immediate description of the principles and conceptual aspects of the invention. In this regard, it is not attempted to show more structural details of the invention than is necessary for a fundamental understanding of the invention. The description in combination with the figures makes it clear for persons skilled in the art how the various forms of the invention can be implemented in practice.

(2) FIG. 1 shows a first embodiment of a pneumatic actuator according to the present invention, and a screw clamp with the pneumatic actuator.

(3) FIG. 2 shows a second embodiment of a pneumatic actuator according to the present invention, and a screw clamp with the pneumatic actuator.

(4) FIG. 3 shows a schematic block diagram of a pneumatic actuator according to the present invention.

(5) FIG. 4 shows a schematic block diagram of a preferred embodiment of a pneumatic actuator according to the present invention, having an adjustable pressure reducer.

(6) FIG. 5 to FIG. 9 show the internal structure of the second embodiment of a pneumatic actuator according to the present invention.

(7) FIG. 5 shows a perspective view of a portion of a preferred embodiment of a pneumatic actuator according to the present invention. The portion shown comprises an adjustable pressure reducer as well as a control valve.

(8) FIG. 6 shows the portion of FIG. 5 in cross-section, from another viewpoint.

(9) FIG. 7 shows the portion of FIG. 5 in another cross-section, through the adjustment knob.

(10) FIG. 8 shows a portion of the screw clamp of FIG. 2 in cross-section.

(11) FIG. 9 shows a portion of the screw clamp of FIG. 2 in another cross-section.

(12) FIG. 10 to FIG. 20 show a third embodiment of a pneumatic actuator and a screw clamp containing the actuator, according to the present invention. This can be seen as a variant of the second embodiment of the pneumatic actuator and screw clamp. FIG. 10 to FIG. 20 are shown as grayscale drawing as well as line drawing, for illustrative purposes.

(13) FIG. 10 shows a screw clamp and a pneumatic actuator according to the third embodiment.

(14) FIG. 11 to FIG. 18 show intermediate steps of a typical sequence or cycle of clamping and releasing once, to explain the internal operation of the pneumatic actuator.

(15) FIG. 11 shows the internal structure of the pneumatic actuator of FIG. 10 in perspective cross-section, before a gas capsule is mounted. The membrane is pushed inwards (to the right) by the spring of the turning knob.

(16) FIG. 12 shows the pneumatic actuator of FIG. 11 after the gas capsule (not shown) is mounted. The membrane is pushed outwards (to the left) by the pressure of the gas from the gas capsule, until the pressure in the first chamber (to the right of the membrane) is greater than the pressure in the second chamber (left of the membrane), thereby closing the shut-off valve between the first chamber and the second chamber.

(17) FIG. 13 shows the pneumatic actuator of FIG. 12, when viewed from another position. The first and the second push button are not depressed.

(18) FIG. 14 shows the pneumatic actuator of FIG. 13 when the first (lowermost) push button is depressed to activate the actuator. A channel is formed from the second chamber to the piston, causing the latter to move (upwards).

(19) FIG. 15 shows the pneumatic actuator of FIG. 14 after the piston has partly moved (upwards).

(20) FIG. 16 shows the pneumatic actuator of FIG. 15 when the first (lowermost) push button (the activation button) is released. The piston remains in the extended position.

(21) FIG. 17 shows the pneumatic actuator of FIG. 16 when the second (top) push button (the relaxation button) is depressed. The gas in the piston escapes, and the piston is pushed back into the retracted position by a spring (visible in FIG. 18).

(22) FIG. 18 shows the pneumatic actuator of FIG. 17 when the piston is fully retracted back and the second push button is released. This is the same state as shown in FIG. 13, differing in that the gas capsule now contains one charge of gas less.

(23) FIG. 19 shows how the screw clamp can be carried with one single hand.

(24) FIG. 20 shows how the screw clamp can be operated with one single hand.

DETAILED DESCRIPTION OF THE INVENTION

(25) The invention will be further explained on the basis of exemplary embodiments. The invention is not limited hereto however, but only by the claims.

(26) The term “1 bar” corresponds with 10.sup.5 Pa.

(27) Screw clamps, also referred to as glueing clamps or glueing cramps, already exist for many decades and, as for their principle of operation, have remained substantially unchanged in the course of time. The clamping principle of a screw clamp relies on the one hand on the fact that the movable arm is slightly tilted when clamping, whereby it assumes a fixed position with respect to the guide profile, and on the other hand on shifting a contact surface with respect to the movable arm by means of a screw. When a screw clamp is to be released, the screw must first be screwed loose, and only thereafter can the movable arm be tilted, after which the movable arm can be slid. The screw clamp is a very robust and reliable tool and is used indoors as well as outdoors.

(28) The inventors of the present invention have however realised that two hands are frequently needed to position the screw clamp, to slide the movable arm and to tighten the screw, in addition to the hands needed to temporarily hold the workpieces in their desired position. As a result, two of three persons are sometimes needed. Moreover the inventors have realised that tightening itself sometimes takes too long, especially when, for example, a large force is to be exerted, e.g. to lift up the workpieces.

(29) In view of these problems, the inventors came to the idea of developing a screw clamp with which workpieces can be clamped faster and more easily, and where less hands are needed to tension this screw clamp. More particularly, the inventors came to the idea of developing a portable screw clamp having a pneumatic actuator with a replaceable gas capsule, the underlying idea being that the screw clamp can be tensioned by pressing a button.

(30) Confronted with this challenge, a first prototype of a screw clamp 100 with a pneumatic actuator 140 was developed and built, shown in FIG. 1. The pneumatic actuator 140 is mainly made of steel and makes use of a gas capsule with CO.sub.2-gas under increased pressure (e.g. with a pressure in the range from 20 to 32 bar) to supply gas under high pressure to a pneumatic cylinder. The pneumatic cylinder comprises a single piston and a spring to push the piston back or to pull it back. A portion of the piston protrudes past the second arm 130 for clamping workpieces (not shown). The pneumatic actuator 140 has two modes of operation, namely: a first mode of operation where the gas capsule is in fluid connection with an inlet of the pneumatic cylinder, whereby the cylinder will move outwards (towards the first arm 120) for clamping workpieces (not shown); and a second mode of operation where the channel of the gas capsule is closed, and the inlet of the pneumatic cylinder is brought into fluid connection with one of more openings 184 to the outside (under atmospheric pressure) so that the gas at the inlet of the piston can escape to the environment, and the spring can push or pull the piston back.

(31) The first prototype 100 (see FIG. 1) was built, but turned out to be less than ideal, and has led to new insights and improvements which will further be described and explained on the basis of FIG. 2 to FIG. 9 as the second prototype 200.

(32) The second prototype was also built and tested, and has led to yet further insights and improvements which will be further described and explained with reference to FIG. 10 to FIG. 20 as the third prototype 300.

(33) As will become clear after reading this document, the principle of operation of the three prototypes is largely the same.

(34) The invention will now be further explained with reference to the figures which describe an exemplary embodiment, without however limiting the invention thereto.

(35) FIG. 1 was already discussed above. It shows the first prototype of a screw clamp 100 with pneumatic actuator 140, attached to the second arm 130 which is slidable over a guide profile 110. In this example, the first arm 120 is unitarily formed with the guide profile 110. One of the disadvantages of the first prototype was that it was too heavy and too large. An additional objective was therefore to make the pneumatic actuator and the screw clamp with the pneumatic actuator as compact as possible.

(36) FIG. 2 shows a second embodiment of a pneumatic actuator 240, and a screw clamp 200 comprising the pneumatic actuator. The screw clamp 200 shown further comprises a guide profile 210 to which a first arm 220 is attached, and over which a second arm 230 is slidably mounted. As shown, the first arm 220 comprises a first contact surface 221, and the second arm 230 comprises a second contact surface 295 facing the first contact surface 221, and which is movable with respect to the second arm 230 such that between the first and second contact surface 221, 295 one or more workpieces can be clamped.

(37) In the example of FIG. 2, the top portion (shown in light gray) of the pneumatic actuator 240 is surrounded by a first metal casing 262, herein also called first protective enclosure. This offers as advantage that the tool is safer in use, especially at the control valve (as will become clear further on) but the casing is not necessary for the functional operation.

(38) In the example of FIG. 2, the lowermost portion (shown in dark gray) of the pneumatic actuator 240 is surrounded by a second metal casing 263, herein also referred to as second protective enclosure. This offers as advantage that the tool is safer in use, especially at the gas capsule (as will become clear further on) but also this casing is not absolutely necessary for the functional operation.

(39) These casings 262, 263 can, for example, be made of aluminium or an aluminium alloy, and may, for example, have a wall thickness in the range from 1.0 mm to 3.0 mm, e.g. equal to about 1.5 mm or about 2.0 mm or about 2.5 mm.

(40) On top of the pneumatic actuator 240, a small cap 294 is provided having the contact surface 295. Dependent on the application, this small cap can be made of steel, or of a plastic, e.g. polyethylene. The latter is especially advantageous for clamping sensitive surfaces, e.g. painted or lacquered objects, without scratching them.

(41) FIG. 3 shows a schematic representation of a pneumatic actuator 240 according to the present invention. As shown, the pneumatic actuator 240 comprises four components: a gas capsule 260 for supplying a gas under increased pressure, e.g. CO.sub.2 gas under a pressure of 20 to 32 bar; a pressure reducer 270, for reducing the pressure of the gas capsule to a lower one, for example predefined pressure in the range from 2 bar to 20 bar, or in the range from 5 bar to 10 bar; a control valve 280 with at least two modes of operation as described above; a pneumatic cylinder 290 with a piston, e.g. a single-acting cylinder with a piston which is movable in a cylinder wall, and with a spring to push the piston back or to pull it back.

(42) It is an advantage to use a gas capsule 260 with a non-combustible gas such as CO.sub.2, because as a result the risk of danger of explosion is strongly reduced, especially when the actuator is used to clamp pieces which, for example, need to be welded.

(43) As shown in FIG. 3, an outlet 261 of the gas capsule 260 is connected with an inlet 271 of the pressure reducer 270, and an outlet 273 of the pressure reducer 270 is connected with an inlet 281 of the control valve 280, and a first outlet 284 of the control valve 280 is connected with an inlet 291 of the pneumatic cylinder 290. The piston or an extension 293 of the piston protrudes at the top of FIG. 3. On this protruding portion 293, optionally a small cap 294 can be provided.

(44) The control valve 280 further comprises a second outlet 285 to the environment, and at least one control pin 282 for determining the mode of operation. The control valve can be a 3/2 valve. Dependent on the specific implementation, the control valve 280 may optionally comprise a second control pin 283, but that is not strictly necessary. In this case, the first control pin 282 is herein also referred to as “activation button”, and the second control pin 283 is herein also referred to as “deactivation button” or “relaxation button”.

(45) The pneumatic actuator 240 may be attached to an arm of the screw clamp 200, e.g. to the movable arm 230 of a screw clamp, where the protruding portion 293 can extend in the space between the first and the second arm (see also FIG. 2).

(46) FIG. 4 shows a schematic representation of a preferred embodiment of a pneumatic actuator 240 according to the present invention. This can be seen as a special embodiment of the pneumatic actuator according to FIG. 3, where the pressure controller is adjustable, and further comprises a setting member 272, e.g. an adjustment knob in the form of a turning knob, but the invention is not limited hereto and other setting members can also be used.

(47) The difference between the schematic drawing of FIG. 3 and FIG. 4 may seem small, but in practice the presence of an adjustable pressure reducer 270 makes a vast difference, on the one hand because, as a result, the clamping force is adjustable (in contrast to the first prototype 100, 140 where the clamping force was fixed), and on the other hand because, as a result, the number of activations for a given type of gas capsule can be dramatically increased.

(48) As far as known to the inventors, no pressure reduction component, intended to deliver discrete amounts of gas supplied at a relatively high pressure of, for example, 20 to 32 bar to an adjustable lower pressure of, for example, 2 to 10 bar, is available. And if such a component does exist, it is questionable whether it meets the requirements of the present invention, in particular in terms of dimensions (compactness) and weight.

(49) Moreover, with the second prototype, the inventors have attempted not only to make the adjustable pressure reducer 270 as compact as possible, but to make the combination of the adjustable pressure reducer 270 and the control valve 280 together as compact as possible.

(50) Further they have attempted to make the space of the channels between the various parts as small as possible, to make the number of activations per gas capsule as large as possible.

(51) It is estimated that with the second prototype a CO.sub.2 gas capsule having an air content of 60 grams under 32 bar, 100 to 150 activations can be carried out, if the reduced pressure is set to 2 bar, before the pressure in the capsule has decreased to 2 bar, and [the capsule] therefore becomes practically unusable. To achieve this, the component was made compact to such an extent that the volume of gas needed per activation (except the first time after a new gas capsule is mounted) is less than 0.025 litre=25 ml, preferably less than 20 ml, with more preference less than 15 ml, e.g. about equal to 13.5 ml. This was a major challenge.

(52) But the invention is not limited to gas capsules with 60 grams of CO.sub.2 under 32 bar, and other gas capsules, e.g. gas capsules with a content higher or lower than 60 grams (e.g. 88 grams) and/or gas capsules with a higher or lower pressure than 32 bar can also be used. Such gas capsules are commercially available and are typically used for pumping up bicycle tyres.

(53) The reader skilled in the art who is familiar with tightening a screw clamp in industrial applications (e.g. in the metal industry and/or building construction) will undoubtedly wonder whether a gas capsule can provide sufficient clamping force. This will be discussed with reference to some examples. 1) a pressure of 2.0 bar exerted upon on a circular surface having a diameter of 30 mm provides a force of about F≈141N. 2) a pressure of 10.0 bar exerted upon on a circular surface having a diameter of 40 mm provides a force of about F≈1256N. 3) a pressure of 20.0 bar exerted upon on a circular surface having a diameter of 50 mm provides a force of about F≈6162N.

(54) These examples show that the clamping force for many applications, also industrial applications, is more than sufficient.

(55) Table 1 gives the clamping force (in Newton) for a variety of diameters d1 of the piston ranging from 30 mm to 60 mm, and for a variety of reduced pressures (at the inlet of the piston) ranging from 2 bar to 20 bar.

(56) TABLE-US-00001 TABLE 1 2 5 10 15 20 bar bar bar bar bar 30 mm 141 353 707 1060 1413 35 mm 192 481 962 1442 1923 40 mm 251 628 1256 1884 2512 45 mm 318 795 1590 2384 3179 50 mm 393 981 1963 2944 3925 55 mm 475 1187 2375 3562 4749 60 mm 565 1413 2826 4239 5652

(57) As can be understood from the table, the piston diameter d1 has an important influence on the clamping force which can be exerted. In preferred embodiments for application in a screw clamp, the piston diameter d1 is a diameter in the range from 30 to 50 mm, e.g. in the range from 35 to 45 mm, e.g. equal to about 40 mm, because this offers an optimal compromise between sufficiently large to supply sufficient force, and sufficiently small due to compactness and ease of handling (ergonomics), but the invention is not limited hereto and other dimensions are also possible.

(58) In all prototypes, the pneumatic actuator 140, 240, 340 has a substantially constant outer diameter over its whole length, or about 60 mm for the first prototype 140, and about 50 mm for the second and third prototype 240, 340, but the invention is not limited hereto, and it is, for example, also possible to use a pneumatic cylinder 290 having a diameter which is larger than the diameter of the control valve 280 for applications where a larger pressure force is needed, as for example a jack to raise an automobile or another vehicle if it has a flat tyre.

(59) FIG. 3 and FIG. 4 are not only valid for the second embodiment, but for all embodiments of the present invention.

(60) FIG. 5 shows a perspective view of a portion of a pneumatic actuator 240 according to the second embodiment of the present invention. The portion shown comprises an adjustable pressure reducer 270 as well as a control valve 280, implemented as a single body, preferably made of plastic, e.g. polyethylene.

(61) In this embodiment, the control valve 280 has a first control pin 282 to activate the piston (which is connected with the outlet 284, but is not shown in FIG. 5), and a second control pin 283 to deactivate the piston. By turning the button 272, the desired pressure to be exerted on the piston can be set.

(62) In a variant (not shown), the adjustment knob 272 may comprise a lever, and/or the adjustment knob 272 may comprise an internal recess for inserting a socket wrench or the like. In this way, a larger torque can be exerted on the adjustment knob 272.

(63) FIG. 6 shows the portion of FIG. 5 in cross-section, when viewed from another viewpoint. The following parts can be distinguished:

(64) At the bottom of FIG. 6 a transition element (adapter) 250 is visible which is preferably made of steel, for example a hardened steel, for example a nitrided steel, for example a nitrided steel having a hardness of at least 55 HRC (Rockwell C hardness), for example with about 60 HRC. In a specific embodiment, nitride steel 1.8550 according to DIN 17211 is used, but the invention is not limited hereto.

(65) The transition element 250 has an internal screw thread 252 configured for mounting a gas capsule with corresponding external screw thread. The transition element 250 has external screw thread 253 for attaching the transition element to the adjustable pressure reducer 270, by engagement in corresponding internal screw thread 274 of the body shown in FIG. 5. The transition element further has a puncture element 254 for puncturing a metal surface of the gas capsule (not shown in FIG. 6 but see FIG. 8 and FIG. 9, for example). Thanks to the threaded connection 252 between the transition element 250 and the gas capsule, an empty gas capsule can easily be replaced by another gas capsule by a user. Thanks to the threaded connection 253, 274, the transition element 250 can be replaced, for example in a specialised repair service, when the transition element 250 is worn. In this way, the lifetime of the pneumatic actuator 240 can be dramatically extended, and thus also the lifetime of the tool in which the actuator is optionally incorporated.

(66) In the middle of FIG. 6 the adjustable pressure controller 270 is shown, but its operation can better be understood from FIG. 7.

(67) At the top of FIG. 6, the control valve 280 is shown, with a first control pin 282 which, when pressed against the force of the spring 288, connects the outlet 273 of the pressure reducer 270 with the outlet 284 leading to the piston, preferably by means of a substantially straight line in order to prevent or reduce pressure loss.

(68) In the particular embodiment shown in FIG. 6, a conical or a spherical object, for example a ball 2821, is used to shut off the channel (between the second chamber and the inlet of the piston), which ball 2821 is slid when the control pin 282 is depressed, but the use of a ball is not strictly necessary and other seals may also be used, for example a control pin with O-rings and having a variable diameter (not shown), or a piston push button as used in the third prototype. The latter can be made of stainless steel, for example, also referred to as RVS or inox.

(69) The control valve 280 of FIG. 6 further comprises a second control pin 283 which, when pressed against the force of the spring 289, connects the outlet 284 to the piston with the second outlet 285, also referred to as outlet into the environment. The second control pin 283, like the first control pin, has an associated spring 289 and a ball 2831, but other sealings are also possible. The skilled person will understand that the ball 2821 and the spring 288 of the first control pin 282 can be inserted via opening 286 during production, the opening subsequently being air-tightly closed off, for example by screwing and/or by glueing and/or melting or in another appropriate manner. In a similar manner, the ball 2831 and the spring 289 of the second control pin 283 can be inserted during production via opening 287, the opening subsequently being air-tightly closed off, for example by screwing and/or glueing and/or melting or the like.

(70) FIG. 7 shows the portion of FIG. 5 in another cross-section, through the adjustment knob 272. From this figure, the operation of the pressure control 270 can be understood.

(71) Gas enters from the gas capsule via the inlet 271 and flows into a first compartment 275 (also called first chamber) which thereby comes under high pressure, for example 32 bar. The first compartment 275 is in fluid communication with a second compartment 276 (also called second chamber) via a passage between the two compartments, which passage can be closed by a valve 277. This valve 277 is connected with a membrane 274 constituting a portion of the wall of the second compartment. The position of the valve 277 in the first compartment 275 is thus dependent on the position of the membrane 274 in the second compartment.

(72) As shown, a spring 279 attempts to push the valve 277 to the left (towards the membrane) in order to close it, and a spring 278 attempts to push the membrane to the right (towards the valve) in order to open the valve. The spring 278 rests against an adjustment knob 272.

(73) The operation is as follows: when the pressure in the second compartment 276 is low (for example about 1 bar), then the membrane 274 is pushed to the right (in FIG. 7) by the spring 278, and the valve 277 is opened, whereby gas under high pressure (for example about 32 bar) from the first compartment 275, which is in connection with the gas capsule, can flow into the second compartment 276. As a result, the pressure in the second compartment 276 rises, and a pressure is exerted on the membrane 274 which moves the membrane 274 to the left (in FIG. 7), against the pressure force of the spring 278. When the pressure in the second compartment 276 reaches a set value, as set by the adjustment knob 272, the valve 277 closes. In this way, an amount of gas at a relatively low pressure (for example 2 bar or 5 bar or 10 bar) can thus be obtained from a gas capsule at relative high pressure (for example 32 bar).

(74) Referring to the functionality of the whole actuator, the second compartment 276 actually functions as an intermediate chamber, and the pressure of the gas in the intermediate chamber is set by the adjustment knob 272. When the actuator is subsequently operated by depressing the control pin 282, then in first instance the gas from the intermediate chamber 276 is distributed to the inlet of the piston, whereby the pressure in the intermediate chamber decreases. The membrane then moves to the right (in FIG. 7), the valve 277 briefly opens, and the gas in the second compartment 276 is supplemented from the first compartment. The valve 277 closes by itself again when the set pressure is reached.

(75) In the case that the control valve is a 3/2 valve, it is also possible to increase the pressure force slightly by turning the adjustment knob 272, even after the workpieces are clamped. In the embodiment of FIG. 7, the pressure force can also be slightly increased by turning the adjustment knob 272, provided the activation button 282 is subsequently depressed again.

(76) In a variant of this embodiment (not shown), the membrane is clamped between two parts each having an annular surface, which parts are mutually connected by means of screw thread, and together constituting the membrane holder 2771. In this way, the membrane can be clamped in over a larger surface, and the risk of the membrane coming loose from the membrane holder is reduced or eliminated.

(77) FIG. 8 shows a portion of the screw clamp of FIG. 2 in cross-section.

(78) From this figure, the operation of the pneumatic cylinder 290 can be better understood. As explained above, upon depressing the first control pin 282, the pressure built up in the second compartment 276 will pass via the outlet 273 of the pressure reducer 270 and via the outlet 284 of the control valve to the inlet 291 of the piston 293, which under influence of the pressure will move outwards (upwards in FIG. 8). As a result the pressure in the second compartment 276 will decrease, the valve 277 will briefly open again until the set pressure in the second compartment 276 is reached again as described above, possibly several times until the piston 293 is fully extended.

(79) When the piston 293 is fully extended, the pressure in the second chamber 276 no longer decreases, and the valve 277 will remain closed. The control pin 282 can be released, whereby the channel between the second compartment 276 and the piston inlet 291 is closed off to prevent leakage.

(80) By depressing activation pin 282, the piston 293 has thus moved upwards in FIG. 8, whereby, in the event of a screw clamp, one or more workpieces can be clamped between the first arm 220 (not shown in FIG. 8 but see FIG. 2, for example) and the second arm 230 of the screw clamp 200.

(81) Obviously the piston 293 is made to fit in the cylinder (for example with tolerance H7) and provided with the necessary sealings (among which 297), so that as little gas as possible can escape unwanted. Such sealings are known per se in the art, and thus need not be explained in more detail.

(82) In the event of a screw clamp, the stroke of the pneumatic cylinder of the pneumatic actuator is preferably chosen in the range from 3 mm to 15 mm, for example from 5 to 12 mm, for example equal to about 8 mm or equal to about 10 mm, but the invention is not limited hereto and another piston stroke can also be chosen. The shorter the piston stroke, the more often the actuator can be operated (for a given gas capsule and a given set pressure force).

(83) In a preferred embodiment the pneumatic cylinder 290 is a single-acting cylinder, with a spring to push the piston 293 back or to pull it back (dependent on how the spring is disposed). In the second embodiment, the spring is a cup spring 296 (in the figure displayed as a flat disc), but that is not necessary, and a classical spring can also be used (as will be further explained, see FIG. 15a or FIG. 18a, for example). The spring 296 ensures that the piston 293 is spontaneously pushed back inwards, after the user has operated the second control pin 283, whereby the pressure at the inlet 291 of the piston 293 is lost. It is an advantage to use a cup spring 296, because this contributes to a large extent to the compactness of the solution. Functionally, the cup spring ensures that the screw clamp releases easily, whereby it can be avoided that the user would need to strike against the second arm 230 with a hammer or the like to release the screw clamp after clamping. There is no pneumatic cylinder known to have a cup spring. The unique combination of the short piston stroke and the compact space makes a cup spring a unique and ideal solution, but the invention is not limited hereto.

(84) FIG. 8 further shows a safety bolt 298 which can be turned in two positions, namely in a locked position and in an unlocked position. In the locked position, the safety bolt 298 has to ensure that the piston can not move outwards, even if a user were to accidentally activate the first control pin 282. In this way, accidents can be avoided.

(85) FIG. 8 further shows that a top unit 294 can be provided on the piston 293, or on an extension thereof, for example by screwing. This top unit 294 can, for example, be made of polyethylene, for example hard polyethylene, and may be attached to the piston (or its extension) by means of screw thread, for example. By making use of an top unit 294 of polyethylene, scratches can be prevented when painted or lacquered objects, for example, need to be clamped. The top unit 294 preferably has a flat surface 295 for clamping objects, but the invention is not limited thereto and other top units are also possible.

(86) In the embodiment of FIG. 8, the extension of the piston or the piston end portion is cylindrically-shaped, but the invention is not limited hereto, and other forms are also possible. In some embodiments, this extension or end portion is spherical, and the top unit 294 which engages with this spherical end portion is somewhat tiltable or rotatable. This has the advantage that also workpieces can be clamped of which opposite surfaces are not perfectly parallel.

(87) FIG. 8 further shows how the pneumatic actuator 240 according to the present invention can be attached to the movable arm 230 of a screw clamp 200. But this aspect is better visible in FIG. 9.

(88) FIG. 9 shows a portion of the screw clamp 200 of FIG. 2 in cross-section.

(89) At the top of FIG. 9, a second arm 230 is displayed with two through-openings 231 and 232. The piston 293 or an extension thereof is provided through the first opening 231, after which the second arm 230 is fixed to the actuator 240, for example by clamping it between two parts of the actuator 240, in the example of FIG. 9, using a ring 201 and a plurality of bolts 202.

(90) As shown, sufficient clearance 299 is provided so that the piston 293 can pass through the opening 231 without touching the second arm 230. Through the second for example rectangular or oval opening 232 of the second arm 230, as common practice, the guide profile 210 is provided. Note that the piston 293 extends far beyond the cylinder 290, which preferably can be very small (for example less than 15 mm high) due to the short stroke.

(91) During normal use, the user sets a desired pressure force by turning the adjustment knob 272, and needs to position the screw clamp appropriately, and needs to move the second arm 230 to against or substantially against the workpieces to be clamped, and needs to subsequently depress the control pin 282, after which the piston 293 will suddenly move and push against the workpieces with the set force.

(92) FIG. 10 to FIG. 20 show a third embodiment of a pneumatic actuator 340 according to the present invention, incorporated in a screw clamp 300 according to the present invention, but, as already mentioned above, the actuator may also be incorporated in other tools.

(93) The pneumatic actuator 340 according to the third embodiment can be seen as a variant of the actuator 240 according to the second embodiment, with as main differences: (1) an ordinary spring 3933 instead of a cup spring 296 to move the piston 393 back to the retracted position, (2) the first push button 382 does not shift a ball or a spherical object 2821, but has a first collar 3821 for forming a first valve 3821, and (3), the second push button 383 does not shift a second spherical object 2831, but has a second collar 3831 for forming a second valve 3831. Apart from these differences, the operation for both actuators is substantially the same. The third embodiment will therefore be only briefly explained. Where possible, as many similar reference numbers as possible will be used (preceded by 3- instead of 2-).

(94) FIG. 10 to FIG. 18 are shown as grayscale drawing as well as line drawing for illustrative purposes.

(95) FIG. 10 shows a screw clamp 300 according to a third embodiment of the present invention. The screw clamp 300 comprises a pneumatic actuator 340 according to a third embodiment of the present invention. Except for the actuator 340, the screw clamp 300 of FIG. 10 is identical to the screw clamp 200 of FIG. 8 and FIG. 9, already described above.

(96) FIG. 11 to FIG. 18 show various intermediate steps of a typical sequence or cycle of clamping and releasing the actuator 340 once. Each of these steps will now be explained in more detail.

(97) FIG. 11 shows the internal structure of the pneumatic actuator 340 of FIG. 10 in perspective cross-section, before a gas capsule is mounted. The inlet 371 of the pressure reducer 370 is connected with the environmental air (with a pressure of substantially 1 bar or substantially 10{circumflex over ( )}5 Pa). The membrane 374 is pushed inwards (to the right in FIG. 11) by the spring 378 of the adjustment knob 372, for example turning knob. The shut-off valve 377 is open. By turning the adjustment knob 372, a desired pressure force can be set in advance. Even though not visible in FIG. 11, the piston 393 is in the fully retracted state (see FIG. 14).

(98) FIG. 12 shows what happens after the gas capsule is mounted (although the latter is not shown for illustrative purposes), assuming that the first and second push buttons 382, 383 are not depressed.

(99) When gas under high pressure (for example 32 bar) enters the first chamber 375 and the second chamber 376, the pressure in the second chamber will rise, whereby the membrane 374 is pushed outwards (to the left in FIG. 12). When the pressure in the second chamber 376 reaches a pre-set value, the shut-off valve 377 is closed, as already described above.

(100) In the third prototype, the amount of gas needed for this “initialisation step” is equal to about 0.004 litre=4 ml, and the amount of gas needed to use the actuator once (activation and deactivation) is equal to about 13.5 ml.

(101) As long as the pressure in the second chamber 374 is greater than or equal to the pressure corresponding to the set pressure force, the shut-off valve 377 remains closed.

(102) FIG. 13 shows the pneumatic actuator of FIG. 12, when viewed from another position. None of the push buttons 382, 383 are depressed. The second chamber 376 is in fluid connection with the space where the spring 388 is disposed, but not further, because the first push button 382, or more particularly a collar 3821 of the first push button 382, forms a first valve 3821, which is closed.

(103) In the example of FIG. 13(a), the control pin 282 is composed of two parts: a part (for example of plastic) situated mainly externally, and an internal part (for example of metal or metal alloy, for example aluminium).

(104) In a variant (not shown), the control pin 282 may be composed of three parts, for example an exterior element (for example of plastic, to avoid the part cooling down too strongly when the button is pressed); and a central element with axial grooves (to avoid the risk of buckling, and at the same time to promote the passage of gas); and an interior portion with a collar. To ensure good sealing in the pressure reducer 270, the interior portion can, for example, be made of a plastic material, for example teflon (also known as PTFE or polytetrafluoroethylene), or ertalon, or nylon or polyamides. Such plastic materials are quite strong, but still somewhat deformable, even at low temperatures as a result of gas which expands. In this way, the sealing can be further improved.

(105) FIG. 14 shows the pneumatic actuator of FIG. 13 when the first push button 382 is depressed against the resilience of the spring 388. Hereby the first valve 3821 is opened, so that the gas can flow from the second chamber 376, along the extension of the first push button 382, through the connecting channel 3822, along the extension of the second push button 383 to the spherical object 3932, which will be pushed up under influence of the gas pressure against the force of the spring 3931, into the cylinder chamber, as designated by the arrow. The space in which the spring 3931 is located, being the cylinder chamber, thus comes under increased pressure, and the piston 393 is pushed outwards (upwards in FIG. 14). When the gas pressure in the second chamber drops to under a value corresponding to the position of the adjustment knob 372, the membrane 374 will move and temporarily open the valve 377 in an attempt to maintain the pressure in the second chamber 376, corresponding to the position of the adjustment knob 372.

(106) FIG. 15 shows the pneumatic actuator of FIG. 14 after the piston 393 is extended (upwards in FIG. 15), under influence of the gas pressure at the bottom in the cylinder chamber, against the force of the spring 3933. The spring 3931 pushes the spherical object 3932 down, and the cylinder chamber is closed off. The spring 3931 and the spherical object 3932 thus form a third valve which was automatically opened due to the increased pressure outside the cylinder chamber after depressing the activation button 382, and which is automatically closed under influence of the spring 3931 when the pressure in the cylinder chamber is substantially equal to the pressure in the second chamber 376.

(107) FIG. 16 shows the pneumatic actuator of FIG. 15 when the first push button 382 is released. The spherical object 3932 ensures that the pressure within the cylinder is maintained. The sealings 397 ensure that substantially no gas can escape, or at least that the leakage is limited as much as possible. When the piston 393 clamps workpieces, they will thus remain clamped.

(108) FIG. 17 shows the pneumatic actuator of FIG. 16 when the second push button 383, also referred to as relaxation button, is depressed. The extension of this push button 383 is implemented such that upon displacement thereof, the spherical object 3932 is pushed upwards, so that gas from the cylinder chamber can escape. Also the second collar is moved, whereby the second valve formed by this collar is opened, so that the gas which escapes from the cylinder chamber is discharged to the environment via the outlet 385. Under influence of a spring 3933 (see FIG. 18), the piston 393 will be pushed back inwards, after which the second push button 383 can be released.

(109) FIG. 18 shows the pneumatic actuator of FIG. 17 when the piston 393 is back in its fully retracted position, and the second push button 383 is released. This is the same state as shown in FIG. 13, differing in that the gas capsule contains one charge of gas less. It is estimated that a gas capsule with 60 grams of CO.sub.2 under 32 bar contains sufficient gas for 100 to 150 activations and deactivations. This number is somewhat dependent on the set pressure force and on the actual piston stroke which the piston has to perform. When the pressure in the gas capsule has decreased too much, the gas capsule needs to be replaced.

(110) FIG. 19 shows an example of how the screw clamp 300 can be carried with one hand.

(111) FIG. 20 shows an example of how the screw clamp 300 can be operated with one hand.

(112) FINALLY, thanks to the choices of materials (for example polyethylene, aluminium piston and cylinder, aluminium casing) the effective end product is ergonomic, lightweight and strong. it is an advantage to use polyethylene for the pressure reducer and the control valve, because this is a strong material, and temperature-resistant (for example from −20° C. to +100° C.), and light weight. even though not explicitly shown in the figures, it is possible to apply an extra thermal insulation between the gas capsule and the aluminium casing 263. In this way, sudden strong cooling off of the aluminium after repeated use of the screw clamp is avoided. In this way, inconveniences and/or potential burn injuries can be avoided. the pneumatic actuator according to the second prototype described above, with dimensions of 50 mm diameter and a length of about 22 cm, has a mass of about 600 grams, and a typical screw clamp containing this actuator has a mass of about 2.2 kg to about 2.5 kg. It is an advantage that this screw clamp can be operated overhead and can be fastened with one simple press of the button. obviously the necessary steps have been taken to ensure that as little as possible gas can escape. For this purpose, among others, O-rings are provided at various places, the openings 286 and 287 along which the spherical object and the spring are inserted are preferably closed by welding or sealed by melting, the dimensions of the piston and the cylinder are matched to each other with a fitting seam (for example with tolerance H7), the piston is provided with the necessary sealings 297, for example sealing flaps, or the sealing is realised by a flat or conical plastic collar (for example teflon) which fits to a complementary aluminium part, etc. preferably also an aluminium casing 262 is crimped around at least the pressure reducer and the control valve in order to further enhance the safety. the prototype was constructed by 3D-printing, but the ultimate plastic body is preferably produced by injection moulding.

REFERENCES

(113) 100 first embodiment of screw clamp (first prototype) 140 first embodiment of pneumatic actuator (first prototype) d2 outer diameter 160 gas capsule 182 control pin (both activation and deactivation) 184 vent hole 180 control valve 190 pneumatic cylinder (piston and cylinder) 200 second embodiment of screw clamp 201 ring 202 bolts 210, 310 guide profile 220, 320 first arm 221 first contact surface 230, 330 second arm 231 first opening 232 second opening 240 pneumatic actuator 250 transition element (adaptor) 254 puncture element 260 gas capsule 261 outlet of the gas capsule 262 first metal casing 263 second metal casing 270, 370 pressure reducer 271, 371 inlet of the pressure reducer (for example reducing valve) 272, 372 adjustment knob of the pressure reducer (for example reducing valve) 273 outlet of the pressure reducer (for example reducing valve) 274, 374 membrane 275, 375 first compartment 276, 376 second compartment 277, 377 shut-off valve 2771 membrane holder 278, 378 first spring 279, 379 second spring 280 control valve 281 inlet of the control valve 282, 382 first control pin of the control valve 2821 ball or spherical object of the first control pin 283, 383 second control pin of the control valve 2831 ball or spherical object of the second control pin 284 first outlet of the control valve 285 second outlet of the control valve 286 first mounting opening 287 second mounting opening 288 spring of the first control pin 289 spring of the second control pin 290 pneumatic cylinder (piston and cylinder) 291 inlet of the pneumatic cylinder 292 cylinder (wall) of the pneumatic cylinder 293, 393 piston of the pneumatic cylinder, or an extension thereof 3821 collar of the first control pin 3822 connection channel 3831 collar of the second control pin 3931 spring for the spherical object of the piston 3932 spherical object at the inlet of the piston 3933 spring to push the piston back 294 top unit 295 second contact surface 296 cup spring 297 seal 298 safety bolt 299 clearance 300 third embodiment of screw clamp d1 diameter of the piston d2 outer diameter of the pneumatic actuator