FIELD OF THE INVENTION

The present invention relates to a pneumatic actuator, and to tools having such an actuator, more specifically a portable screw clamp having such an actuator.

BACKGROUND OF THE INVENTION

Pneumatic actuators are known in the art. They are usually used in an automatic production line for moving objects, in which they are provided with compressed air via a supply line coupled with a compressor.

Screw clamps, also known as glueing clamps or glueing cramps, are also known in the art. They are widely used in the metal industry and in building construction, to clamp parts prior to welding them or drilling them or otherwise attaching them. Existing screw clamps have a guide profile with a fixed arm and a movable arm, the movable arm being slidable over the guide profile, and the movable arm having a screw clamp for clamping workpieces. When clamping, the movable arm is typically first slid towards the fixed arm against the workpieces, and subsequently the screw clamp is manually screwed tight.

Such screw clamps are described, for example, in U.S. Pat. Nos. 5,427,364A and 6,123,326A. BE1010202A3 en FR2615888A1 describe screw clamps wherein the fixed arm has a pointed end.

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to provide a pneumatic actuator which can be used in a portable tool, more specifically a freestanding tool (i.e. non-coupled to a supply line) and a tool that can be carried in one hand, and a method for assembling such an actuator.

It is an object of embodiments of the present invention to provide a portable tool (e.g. a screw clamp) which can be operated with one hand, and a method for assembling such a tool, and a method for repairing such a tool.

It is an object of embodiments of the present invention to provide a portable tool (e.g. a screw clamp) which can be quickly clamped.

It is an object of embodiments of the present invention to provide a portable tool (e.g. a screw clamp) which can be quickly released.

It is an object of embodiments of the present invention to provide a portable tool (e.g. a screw clamp) which can be clamped with a pre-adjustable force.

For this purpose, the present invention provides a pneumatic actuator, and a tool comprising such a pneumatic actuator, and a method for assembling such a tool, and a method for repairing such a tool, according to embodiments of the present invention.

According to a first aspect, the present invention provides a pneumatic actuator, comprising: a replaceable gas capsule having a capsule outlet, for supplying a gas under elevated pressure; a pressure reducer connected with an outlet of the gas capsule, adapted for delivering 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 having a piston which is movable from a retracted position to an extended position.

It is an advantage of such an actuator that it can work on its own, and thus does not need to be connected to a compressor via a hose. This makes the actuator extremely suitable for portable applications.

It is an advantage that the actuator converts pressure force from the gas capsule into a linear movement with a certain force. This makes the actuator extremely suitable for application in a screw clamp or a stut or the like.

It is an advantage that a pressure reducer is used, because as a result (during activation) not the full pressure of the gas capsule is supplied to the pneumatic cylinder, but only a lower pressure. As a result, the pressure force exerted by the pneumatic cylinder can deliberately remain limited, and the number of activations can also be increased.

Preferably the pressure reducer comprises at least one movable element.

Preferably the pressure reducer comprises at least a first compartment fluidly connected with a second compartment via a passage, which passage is closable by means of a valve, which valve is connected with a membrane and with at least one spring, and where the membrane and the valve and the at least one spring are arranged such that the valve opens when pressure in the second compartment is less than a predefined or pre-set pressure, and that the valve closes when pressure in the second compartment is greater than the predefined pressure.

The gas capsule preferably contains CO2at a pressure of at least 20 bar. CO2is a non-combustible gas. This offers the advantage that the risk of explosion upon normal use is minimal.

The pressure reducer preferably has an inlet for receiving gas under increased pressure, and an outlet for delivering gas under a reduced pressure.

The control valve preferably has an inlet fluidly connected with the outlet of the pressure reducer, and preferably has a first outlet for supplying the gas under the reduced pressure, and a second outlet to the environment.

The pneumatic cylinder preferably has a cylinder inlet fluidly connected with the first outlet of the control valve, and a piston which is movable from a retracted position to an extended position.

The gas capsule preferably has a capsule outlet connected with the inlet of the pressure reducer, for supplying the gas under increased pressure.

Preferably in the first mode of operation the inlet of the control valve is fluidly connected with its first outlet for moving the piston from the retracted to the extended position.

Preferably the actuator has a first mode of operation for moving the piston from the retracted to the extended position, and a second mode of operation for retracting the piston.

Preferably in the second mode of operation the first outlet of the control valve is fluidly connected with its second outlet for letting the gas escape from the pneumatic cylinder into the environment.

In an embodiment, the pressure reducer is an adjustable pressure reducer, and the pressure reducer has an adjustment knob for adjusting a pressure at the outlet of the pressure reducer.

It is a strong advantage to provide an adjustable pressure reducer, in contrast to a pressure reducer with an unadjustable pressure, because this allows the force of the pneumatic cylinder, more particularly of the piston, to be made adjustable, dependent on the application. This is advantageous, for example, when the actuator is used in a clamp of a screw clamp or the like, because this allows the user to adjust the force with which objects are clamped, for example sufficiently large (e.g. greater than a certain threshold of e.g. 100 Newton) so that the clamped objects do not come loose, and sufficiently small (e.g. smaller than a certain threshold of e.g. 2500 Newton) in order not to damage the objects.

The adjustable pressure reducer may have a similar structure as a reducing valve. And even though it is known to position a reducing valve between two lines in which a gas is flowing continuously, as for supplying a combustible gas to a gas fire from a gas bottle, to prevent shocks, it is not known to use a reducing valve for a discontinuous application in which only very briefly a small amount of gas has to be supplied at once. And neither is it known to incorporate a reducing valve in an actuator which can be carried in and be controlled by a single hand.

It has proved surprising that it is possible to construct a very compact adjustable pressure reducer which fits in an imaginary cylinder having a diameter of 5 cm and a height of 5 cm, but also that such a pressure reducer works surprisingly well for reducing pressure of short discrete loads originating from a gas capsule with a relative high pressure (e.g. more than 20 bar, or even more than 25 bar, or even more than 30 bar).

In an embodiment, the pneumatic cylinder comprises a cylinder wall having an internal diameter of 30 to 60 mm, and a piston which is movable with respect to the cylinder wall.

It is an advantage of such a diameter that, when a pressure of about 2 to 20 bar is exerted on it, the piston can supply a force of about 141 to about 5652 Newton.

In an embodiment, the pneumatic cylinder has a piston stroke in the range from 3 mm to 15 mm, e.g. from 5 to 12 mm, e.g. equal to about 6 mm or about 8 mm or about 10 mm.

In an embodiment, the pneumatic cylinder is a single-acting pneumatic cylinder, with a spring for at least partially pushing back the piston.

The spring may be a cup spring. It is an advantage to use a cup spring, because these are significantly smaller and more powerful than a coil spring of the same outer diameter. As a result, the space needed to contain the spring can be strongly reduced, which benefits the compactness. A cup spring is especially advantageous in combination with a small piston stroke.

The spring may also be a classical cylindrical spring.

It is an advantage to use a single-acting cylinder instead of a double-acting cylinder, because this simplifies the design of the actuator significantly.

Even though the present invention can also work without a spring to push the piston back inside (in this case the user can push the piston back manually, for example), the spring offers the advantage that the piston is at least partially pushed back automatically. As a result, the actuator can be deactivated faster and more easily. Without the presence of the spring, a hammer is needed to relax the bracket, even when the piston is no longer actively pushing.

In an embodiment, the outlet of the gas capsule is fluidly connected with the inlet of the pressure reducer via a transition element (adapter); and the pressure reducer has an internal screw thread for attaching the transition element, and the transition element comprises a corresponding external screw thread; and the transition element further comprising an internal screw thread for attaching the gas capsule, and the gas capsule comprising a corresponding external screw thread; and the transition element further comprising a puncture element for puncturing a part of the gas capsule during the mounting of the gas capsule in the transition element, and the puncture element being fluidly connected with the inlet of the pressure reducer.

It is a major advantage to make the transition element as a separate component, because this allows other materials to be used for the reducing valve on the one hand, and the transition element on the other hand. As a result, the properties of the elements can be optimised separately.

This further offers the advantage that the transition element is replaceable. This is advantageous because the internal screw thread and the puncture element of the transition element in particular are subject to wear.

In an embodiment, the transition element is made of nitride steel, and the pressure reducer comprises polyethylene.

It is an advantage of nitride steel that it can be hardened.

In an embodiment, the cylinder wall and the piston of the pneumatic cylinder are made of aluminium or an aluminium alloy.

This offers the advantage that the pneumatic cylinder can be implemented both lightweight as well as very strong.

The aluminium alloy is preferably an AlMgSi alloy. This alloy has the advantage that it can be hardened.

In an embodiment, the pneumatic actuator has internal channels having a diameter of at most 8 mm, e.g. about 7 mm, or about 6 mm, or about 5 mm, or about 4 mm, or about 3 mm.

Such channels are, on the one hand, sufficiently large to limit the pressure loss upon passage of gas, and constitute, on the other hand, a sufficiently small space to limit the amount of gas consumed per activation and deactivation.

By choosing channels of 6 mm instead of 8 mm, the number of activations (for a given gas capsule and set pressure force) can be increased. On the other hand, to limit pressure loss, the channels should not be too small, especially if there are bends.

In an embodiment, the gas capsule is surrounded by a cylinder-shaped metal casing of at least 1.5 mm thickness, with an external diameter of 45 mm to 65 mm.

In a preferred embodiment, the outer diameter is about 50 mm or about 60 mm or about 55 mm thick. Such a cylinder can be firmly held in the hand.

The metal is preferably aluminium or an aluminium alloy, e.g. an AlMgSi alloy.

Such metal casing also offers extra protection to the user against the unwanted disengagement of some part of the actuator under high pressure. By doing this, the risk of possible injuries is strongly reduced.

In an embodiment, the gas capsule is surrounded by a thermal insulation provided within the aluminium casing.

The thermal insulation may help to prevent burn injuries which might occur upon direct contact of the human skin with the gas capsule, because ice formation could occur around the gas capsule if it is used regularly.

In an embodiment, the control valve has an internal space which 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 the first mode of operation, or with the second outlet of the control valve corresponding to the second mode of operation.

It is an advantage of such a control valve that the piston of the pneumatic cylinder is permanently under increased pressure (e.g. a pressure of 2 to 20 bar) when the control pin is in the first position, so that any small pressure losses can be supplemented from the capsule.

This operation is also easy to understand for a user.

The control pin can be a cylinder-shaped pen, for example, arranged in transversal direction with respect to the control valve, and may have a variable diameter.

In an embodiment, 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 the first control pin back to a position where the first outlet is closed off from the inlet; and 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 for pushing the second control pin back to a position where the first outlet is closed off from the second outlet; and where the first mode of operation corresponds to the first control pin being in the depressed position and the second control pin being in pushed-back position; and where the second mode of operation corresponds to the second control pin being in the depressed position and the first control pin being in the pushed-back position.

By ‘depressed position’ is meant the position where the pen is pushed inwards. By ‘pushed-back position’ is meant the position where the pen is pushed outwards.

In an embodiment, the pneumatic actuator is implemented such that for each activation and deactivation less than 25 ml gas from the gas capsule is used, e.g. less than 20 ml.

It is an advantage that the pneumatic actuator can be implemented very compactly, so that it can quite easily be held in a single hand.

It is an advantage that the internal space of the pneumatic actuator is limited; the smaller the space, the more activations are possible with a given gas capsule.

In an embodiment, the pneumatic actuator without the gas capsule has a mass of less than 700 grams, e.g. less than 650 grams, e.g. less than 600 grams.

Such an actuator is extremely suitable for use in tools which must be operable with a single hand, even in an overhead position.

According to a second aspect, the present invention provides a method for assembling a pneumatic actuator according to the first aspect, the method comprising the steps of: 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 (or flange) and at least one spring in a first opening of the body; sealing the opening at the side of the spring; screwing in a hardened transition element in the body; heating a first aluminium casing, and applying it in heated state around the body, and crimping it.

In an embodiment, the method further comprises the step of inserting at least a second control pin and at least a second ball or a second element having a collar, and at least a second spring in a second opening of the body.

In an embodiment, the method further comprises the steps of: applying a second metal casing against the body, for surrounding the space configured for accommodating the gas capsule.

Preferably the metal is aluminium or an aluminium alloy.

Preferably the second metal casing is attached by means of a threaded connection around the place where the gas capsule is contained.

According to a third aspect, the present invention provides a clamping device with a pneumatic actuator according to the first aspect; and with a first arm forming part of a guide profile or to which a guide profile is connected, the guide profile having a linear part; and a second arm movably attached to the linear part of the guide profile, the second arm having two through-openings; and the first arm and the second arm extending substantially perpendicular with respect to the linear part of the guide profile; and the pneumatic actuator being connected with the second arm and extending in a direction substantially parallel to the linear part of the guide profile for clamping one or more workpieces.

Such a clamping device can also be called a “screw clamp”.

Such a screw clamp has the advantage that it can be operated with a single hand, even in an overhead position, as opposed to a classical screw clamp where one hand is needed for holding, and one hand is needed for screwing the tensioning screw of the screw clamp tight. Or in other words, for tasks where with the classical screw clamp 3 or 2 persons were needed to hold and tension the pieces, 2 persons or 1 person can suffice using a screw clamp according to the present invention.

It is an advantage of this “clamping device with pneumatic actuator”, herein also called “automatic screw clamp”, that a workpiece can be clamped very quickly, much faster than with a classical screw clamp which has to be screwed tight manually.

It is an advantage of embodiments having an adjustable reducing valve that the clamping force can be set easily and can be set beforehand.

In an embodiment, 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.

Flat surfaces offer the advantage (as compared to toothed surfaces for example) that sensitive surfaces, e.g. painted or lacquered surfaces, can be clamped without any or without significant damage.

In an embodiment, the mass of the clamping device amounts to less than 2600 grams, e.g. less than 2400 grams, e.g. less than 2200 grams.

It is an advantage of such a clamping device (e.g. a screw clamp) with such a relatively low weight that it can be easily held with one hand, even in an overhead position. This low weight is achieved by the small dimensions, and by making use of a variety of light materials, among which aluminium or aluminium alloy for the pneumatic cylinder, by making the hardened steel element as small as possible (e.g. by making use of an insert), and by making as much use as possible of plastic material, for example polyethylene, for the remaining components.

In an embodiment, the clamping device further comprises a safety bolt to block the piston.

It is an advantage of the safety bolt that it prevents the piston from moving outwards, because the safety bolt restrains the piston. In this way (under certain circumstances) it can be prevented that a person accidentally clamps his or her fingers.

According to a fourth aspect, the present invention provides a method for assembling a clamping device according to the third aspect, the method comprising the steps of: a) providing a pneumatic actuator according to the first aspect; b) providing a guide profile with a linear part with a first arm forming part of the guide profile; or providing a guide profile with a linear portion, and providing a first arm, and connecting the first arm to the guide profile; c) providing a second arm with a first opening and a second opening; d) connecting the pneumatic actuator to the first opening of the second arm; d) inserting the guide profile through the second opening of the second arm.

In an embodiment, the method further comprises the step of connecting a top unit to the piston or to an extension of the piston.

According to a fifth aspect, the present invention provides a method for repairing a clamping device according to the third aspect, the method comprising the steps of: a) providing a clamping device according to the first aspect; b) if present, removing the gas capsule; c) removing the hardened transition element (or adapter); d) screwing in a new hardened transition element.

This method is extremely suitable for the repair of a clamping device of which the transition element is damaged or worn.

According to a sixth aspect, the present invention provides a tool comprising a pneumatic actuator according to the first aspect, preferably a portable tool.

