Patent Description:
Preferably, the pneumatic cylinders according to the invention are used in industrial plants producing, inter alia, sawn goods, more briefly in sawmills, to quickly lower and raise a rotating saw blade to a sawing position and up therefrom, respectively. At this site of application, the pneumatic cylinder reciprocating extremely fast, is referred to, inter alia, as a trimmer cylinder. The pneumatic cylinders according to the invention have many other applications.

In order to operate properly in the intended application, the trimmer cylinder must be very fast, durable and maintenance-free. Further, the trimmer cylinder must be capable of enduring external mechanical stress and be not responsive to dirt, such as pitch present in sawmills. Further, one of the most important requirements imposed on the fast reciprocating trimmer cylinder is that the end damping of the trimmer cylinder must be exceptionally good.

The prior-art pneumatic cylinders acting as trimmer cylinders suffer from the problem that they, in order to operate properly, must be adjusted very frequently. Especially, adjusting their damping is very important and must be done far too often for the current cylinders. If not adjusted frequently enough, the cylinders break down or malfunction. The need for adjustment is mainly due to the fact that the elastic seals of the cylinders requiring grease lubrication wear out and due to friction variation during use. The operations that must be adjusted include, inter alia, end damping and stroke speed. In addition, for a successful adjustment, it is often necessary to adjust the operating pressure applied to the cylinder as well. These adjustments are laborious, difficult and very time-consuming to carry out as there often are many trimmer cylinders in parallel and the individual trimmer cylinders must often be adjusted at different times. Further, the prior-art pneumatic cylinders acting as trimmer cylinders suffer from the problem that an experienced person is needed to put them into use. The current solutions attempt to solve this problem, inter alia, by adding, not only a main valve but also several other valves to the control system of the trimmer cylinders used in sawmills, in order to control the damping. Thus, the damping is adjusted by constricting the outlet air orifice by the valves. However, the extra valves result in higher costs and make the structure of the cylinder unit more complicated and more prone to malfunction. Besides, the extra valves increase the need of maintenance and adjustments. The structure and fasteners of the cylinders have also been strengthened in order to solve the durability problem. But, this is also cost-increasing and adds weight to the structures. Further, another problem is that, the wear-resistance of the cylinders being already extremely stretched out, the current solutions do not allow the production rate to be easily increased.

One prior art solution is presented in document <CIT>. In the solution a high pressure air is supplied into an air chamber through an air tube from a first changeover valve. Piston shifts in first direction and the air in an air chamber is exhausted into an opened port part from a fitted part through an air tube and second changeover valve. The piston shifts further, and when stopper, which can be fitted to the recessed part of a housing and which is installed onto a piston rod, passes through the opened port part the air in the fitting part can not be exhausted from the opened port part because of an air cushion seal and is exhausted through an orifice.

The present invention aims at alleviating, or even eliminating, the prior-art problems stated above. Thus, an objective of the present invention is to provide a reliable and maximally maintenance-free arrangement comprising a pneumatic cylinder, especially a trimmer cylinder used in sawmills. This arrangement can be implemented, for example, by omitting as many seals as possible, susceptible to wear and requiring lubrication, and/or by replacing the sealing material with one requiring no lubrication, in the structure. Another objective of the invention is to provide an arrangement comprising a pneumatic cylinder, especially a trimmer cylinder, allowing the fast piston movement damping to be effectively adjusted and, as a result thereof, harmful pressure peaks to be avoided. This allows for effective prevention of an abrupt rearward movement, caused by a pressure peak of the trimmer cylinder, for example, at the end of the movement of the piston rod. This movement could result in an excessive temporary change of the position of the saw blade, for example, and give an undesired sawing result on the quickly moving wood material.

To achieve the above-mentioned objectives, the arrangement comprising a pneumatic cylinder according to the invention is characterized in what is set forth in the characterizing part of claim <NUM>. Other embodiments of the invention are characterized in what is set forth in the rest of the claims.

A typical pneumatic cylinder of the arrangement according to the invention comprises a rear end, a front end and a pressure space therebetween, the pressure space containing a piston reciprocating in the pressure space and having a piston rod whose free end is arranged to project out of the pressure space, through a structure provided in the front end and guiding the piston rod. Further, the pneumatic cylinder comprises a first pressure medium flow channel leading to a first side of the piston and a second pressure medium flow channel leading to a second side of the piston, as well as structures damping the reciprocating movement of the piston at the extreme ends of the piston. A play is provided between the structure guiding the piston rod and the piston rod to conduct the pressure medium out of the pressure space during the movement of the piston rod.

A major advantage of the solution according to the invention is that the movement of the piston of the pneumatic cylinder according to the invention can be very quick, the damping of the movement still working reliably. Non-return valves can be provided in the structure to contribute to the quick launch of the piston. Another advantage of the quick movement is that it allows the production rates to be increased without causing harm to the equipment. Another advantage is that the pneumatic cylinder is easy to put into use and is low-maintenance. This results in a long maintenance interval in comparison with the prior-art solutions. Another advantage is that it is possible to effectively adjust the damping of the movement the piston and, as a result thereof, to avoid harmful pressure peaks. This allows for effective prevention of an abrupt rearward movement, that is, bouncing, caused by a pressure peak of the trimmer cylinder, for example, at the end of the movement of the piston rod. Therefore, the trimmer cylinders used sawmills, for example, are able to give a more reliable sawing result. Still another advantage is that it is possible, during the minus stroke of the piston, that is, during the entrance movement of the piston rod, to effectively prevent dirt from entering the pneumatic cylinder and, thereby, from obstructing the structures. Still another advantage is that the structure according to the invention does not cause any significant friction to the movement of the piston or of the piston rod. Thus, the sealing and bearing structure is also almost wear and maintenance free. Still another advantage is that the fastening structure of the fastener at the rear end of the cylinder damps, for its part, the mechanical clanging of the cylinder.

In the following, the invention will be described in more detail by means of examples, with reference to the schematic and simplified drawings where.

The Figures show the structure of the pneumatic cylinder in a simplified form, not necessarily depicting all of its structural parts. Further, for clarity, the valve structures and a part of the pressure medium flow channeling only are symbolically designated in the Figures. Gas, preferably air, below referring to any appropriate pressure medium, is used as the pressure medium.

<FIG> is a simplified lateral view of a pneumatic cylinder according to the invention, preferably operating as a sawmill trimmer cylinder, and with the piston rod <NUM> almost retracted. The pneumatic cylinder comprises a cylinder member fastener <NUM>, a cylinder member rear end <NUM>, a cylinder tube <NUM>, a cylinder member front end <NUM>, a piston with a piston rod <NUM>, a sealing arrangement <NUM> to seal against a flow leaking from the front end <NUM>, and a fastener <NUM> of the piston rod <NUM> as well as flow channels, flow paths, valves, regulators, bearings and seals provided, inter alia, in the cylinder member and the piston and not shown in <FIG>.

<FIG> are simplified lateral and partially cross-sectional views of the pneumatic cylinder shown in <FIG> shows the pneumatic cylinder in an assembled state and with the piston rod <NUM> almost retracted. <FIG> is a partially cross-sectional view of the cylinder member only, without the piston member, while <FIG> is a partially cross-sectional view of the piston member only, with its components. <FIG> show a first and a second restricting structure, that is, a first flow restrictor <NUM> and a second flow restrictor <NUM> intended for restricting the amount of the flow leaving during damping. <FIG> are specifically simplified to make the plays 24a and 18a of the flow restrictors clearly visible in the Figures.

The rear end <NUM> and the front end <NUM> of the cylinder member are hermetically sealed with respect to each other, by the preferably cylindrical cylinder tube <NUM> enclosing a space for the movement of the piston <NUM>, that is, a pressure space <NUM>. The rear end <NUM> has a first flow channel <NUM>, preferably connected to a source of compressed air, such as a compressor, via a control valve. The flow channel <NUM> also connects to the pressure space <NUM>, via a non-return valve <NUM>, a damping regulating flow path 14a, a constant-flow path 14b and a central channel 16a of a first damper <NUM>. To adjust the damping, a regulator <NUM> regulating the maximum pressure of the air flow leaving at the damping step is provided along the damping regulating flow path 14a. According to the invention, the damping is adjusted by regulating the maximum pressure of the air flow. The central channel 16a is located in the cylindrical and cantilevered damper <NUM> extending coaxially with the piston <NUM>, in the pressure space <NUM>, from the rear end <NUM> towards the front end <NUM>. For the damper <NUM>, the center axis of the piston <NUM> is provided with a cylindrical borehole constituting a first damper withdrawal space <NUM> whose diameter exceeds the outer diameter of the damper <NUM>. The first damper withdrawal space <NUM> extends into the piston <NUM> and the piston rod <NUM>, the diameter of the damper withdrawal space <NUM> being smaller than the diameter of the piston rod <NUM> at the damper withdrawal space23. When the piston rod <NUM> is fully retracted, the damper <NUM> projects into the damper withdrawal space23.

In proximity to the open end of the first damper withdrawal space <NUM>, the damper withdrawal space <NUM> contains the first structure <NUM>, that is, the first flow restrictor <NUM>, restricting the amount of the flow exiting during the damping of the entrance movement of the piston <NUM> and preferably constituted by a separate damping ring, for example, but it can just as well be a short annular projection extending towards the center axis of the damper withdrawal space <NUM> and having a diameter smaller than that of the rest of the damper withdrawal space <NUM>. In this case, the projection acting as the first flow restrictor <NUM> preferably consists of the same material as the piston <NUM>. The flow restrictor <NUM> creates a choke between the damper <NUM> and the first damper withdrawal space <NUM> to restrict the air flow at the step of damping the movement of the piston <NUM>. Suitably, the flow can also be restricted without a separate projection, by giving the diameter of first damper withdrawal space <NUM> suitable dimensions, as shown in <FIG>.

The projection of the first damper <NUM> into the piston <NUM> allows for a short structural length of the pneumatic cylinder.

Preferably, the inner diameter of the first flow restrictor <NUM> exceeds the outer diameter of the first damper <NUM> in order to leave a narrow play 24a between the inner diameter of the flow restrictor <NUM> and the outer diameter of the damper <NUM>, for the air flow, the damper <NUM> thus not sealingly contacting the first flow restrictor <NUM>. Accordingly, the first damper <NUM> is adapted to run in the first damper withdrawal space <NUM>, contactlessly with respect to the first flow restrictor <NUM>.

Correspondingly, the front end <NUM> of the pneumatic cylinder has a second flow channel <NUM>, preferably connected, via a cylinder connector, to a source of compressed air, such as a compressor. The second flow channel <NUM> is also connects to the pressure space <NUM>, via a non-return valve <NUM>, a damping regulating flow path 15a, a constant-flow path 15b and a second damper withdrawal space <NUM>. To adjust the damping, a regulator <NUM> regulating the maximum pressure of the air flow leaving at the damping step is provided along the damping regulating flow path 15a. Also in this case, the damping is adjusted by regulating the maximum pressure of the air flow. The damper withdrawal space <NUM> is connected to a structure provided in the front end <NUM>, extending from the end face of the front end and guiding the piston rod <NUM>, such as to a borehole where the piston rod <NUM> is positioned to move. Below, a shorter term, "borehole <NUM>", will also be used. The inner diameter of the borehole <NUM> exceeds the outer diameter of the piston rod <NUM> in the borehole, leaving a narrow play <NUM> therebetween for the pressurized air flow.

The constant-flow paths 14b and 15b allow for and ensure a controlled and terminal discharge of pressure from the cylinder when the movement of the cylinder stops. Because the regulators <NUM> and <NUM> close as the pressure drops below a set level, the controllable pressure-regulating path does not release the pressure to zero level.

In proximity to the end of the second damper withdrawal space <NUM> opening into the pressure space <NUM>, the damper withdrawal space <NUM> has the second structure <NUM>, more briefly, the second flow restrictor <NUM>, restricting the amount of the flow leaving during damping and preferably constituted, for example, by a separate damping ring, but it can just as well be a short annular projection extending towards the center axis of the damper withdrawal space <NUM> and having a diameter equal to or smaller than that of the rest of the damper withdrawal space <NUM>. In this case, the flow restrictor <NUM> preferably is made of the same material as the front end <NUM>. The second flow restrictor <NUM> creates a choke between the extension of the piston rod <NUM>, that is, the outer diameter of the piston-like second damper <NUM> and the second damper withdrawal space <NUM> in order to restrict the air flow. It is also possible to create a functional structure without a separate damping ring or a projection-like choke, by suitably interdimensioning the second damper <NUM> and the damper withdrawal space <NUM> in such a way that a small play to restrict the flow in a suitable way is created, as will be shown below in the solution according to <FIG>.

Preferably, the inner diameter of the second flow restrictor <NUM> exceeds the outer diameter of the second damper <NUM>, leaving narrow play 18a between the inner diameter of the flow restrictor <NUM> and the outer diameter of the damper <NUM>, for the air flow, the damper <NUM> thus not sealingly contacting the second flow restrictor <NUM>. Accordingly, the second damper <NUM> is adapted to travel in the second damper withdrawal space <NUM>, contactlessly with respect to the second flow restrictor <NUM>.

Suitably, the cylindrical diameter of the actual piston <NUM> is smaller than the inner diameter of the cylinder tube <NUM>. Besides, the piston <NUM> is sealed against the cylinder tube <NUM> by a lubrication-free sealing <NUM>, preferably made of PTFE material. The base of the piston <NUM> has a shoulder-like extension projecting towards the exit end of the piston rod <NUM>, that is, its free end, and acting as a the second damper <NUM> whose diameter exceeds the diameter of the rest of the piston rod, from the damper <NUM> towards the free end of the piston rod <NUM>. The free end of the second damper <NUM> has a bevel 22a allowing, at the beginning of the damping step, the damper <NUM> to smoothly and substantially contactlessly pass through the second flow restrictor <NUM> provided in the free end of the second damper withdrawal space <NUM>.

The first damper <NUM> with its central channel 16a, the first damper withdrawal space <NUM> and the first flow restrictor <NUM>, as well as the second damper <NUM>, the second damper withdrawal space <NUM> and the second flow restrictor <NUM> constitute the main structures for damping the reciprocating movement of the piston <NUM> of the pneumatic cylinder according to the invention, at the extreme ends of the movement. Preferably, said structures for damping the reciprocating movement of the piston <NUM> at the extreme ends of the movement also comprise the flow paths 14a, 14b, 15a and 15b with the regulators <NUM> and <NUM>.

For a quick launch of the piston, it is preferable that the cross-sectional area of the flow path of the non-return valve <NUM> provided between the pressure space <NUM> and the first flow channel <NUM> exceeds the combined cross-sectional area of the flow paths 14a, 14b and 16a connecting, from the pressure space <NUM>, to the first flow channel <NUM> and participating in the damping of the movement of the piston <NUM>. Correspondingly, it is preferable that the cross-sectional area of the non-return valve <NUM> provided between the pressure space <NUM> and the second flow channel <NUM> exceeds the combined cross-sectional area of the flow paths 15a, 15b and the play 18a participating in the damping of the movement of the piston <NUM>.

Additionally, a sealing arrangement <NUM> is provided at the free end of the piston rod <NUM>, comprising a preferably annular sealing element 6a, a first mating surface 6b and a second mating surface 6c, the sealing element 6a being adapted to be pressed between these mating surfaces 6b and 6c by the movement of the piston rod <NUM>. Preferably, the sealing element 6a is made of elastic material and adapted to seal against a cylinder air leak when the piston rod <NUM>, at the end of its minus stroke, is fully retracted. The first mating surface 6b is stationary with respect to the cylinder member and located on the front face of the front end <NUM> of the cylinder Correspondingly, the second mating surface 6c is adapted to move along with the piston rod <NUM>. In the exemplifying embodiments according to the Figures, the second mating surface 6c is located on a separate flange <NUM> attached to the piston rod <NUM> but it can just as well be located on the end face of the fastener <NUM> of the piston rod <NUM>, facing the front end <NUM>, as will be shown below in <FIG>. The mating surfaces 6b and 6c are opposite to each other, the sealing element 6a being provided between the mating surfaces 6b and 6c. In the exemplifying embodiments, the sealing element 6a is attached to the second mating surface but it can just as well be a separate structure freely floating on the piston rod <NUM> and, therefore, easier to replace than a fixed sealing element 6a. Limiting the speed of the movement of entrance pneumatically by means of the structure <NUM> allows for a longer maintenance interval of the sealing element 6a.

In the solution according to the invention, the sealing after the minus stroke of the piston <NUM> takes place as a load connected to the piston rod <NUM>, or following the movement of the piston rod <NUM>, reaches, through the power of the movement of the piston <NUM>, a desired position consistent with the minus stroke. Thus, the sealing mating surface 6c and the load <NUM> moved by the piston move simultaneously.

<FIG> show the pneumatic cylinder according to the invention in situations where the piston <NUM> and the piston rod <NUM> are in their two extreme positions. In <FIG>, the piston rod <NUM> and the second damper <NUM> are in a fully extended extreme position and in the second damper withdrawal space <NUM>, respectively. As the piston <NUM> moves, pressurized air exits the cylinder, through the narrow play <NUM> between the piston rod <NUM> and the borehole <NUM> of the front end. Correspondingly, in <FIG>, the piston rod <NUM> and the first damper <NUM> are in a fully retracted extreme position and in the first damper withdrawal space <NUM>, respectively. The sealing element 6a is tightly pressed against the mating surface 6b provided on the front face of the front end <NUM> and blocks the play <NUM>, with the result that no pressurized air can come out of the cylinder, through the narrow play <NUM> between the piston rod <NUM> and the borehole <NUM> of the front end.

<FIG> show two different preferred exemplifying embodiments of the invention. In the structure according to <FIG>, the piston <NUM> and the piston rod <NUM> are provided with sliding bearings. Thus, the piston <NUM> is mounted on the inner surface of the cylinder tube <NUM> by one or more, preferably lubrication-free sliding bearings <NUM> while the piston rod <NUM> is mounted on the inner surface of the borehole <NUM> of the front end <NUM> by one or more, preferably lubrication-free sliding bearings <NUM>. The bearings allow for a very precise radial movement of the piston <NUM> and the piston rod <NUM>, making it possible to reduce the play 24a between the first damper withdrawal space <NUM> and the first damper <NUM> as well as the play 18a between the inner surface of the second damper withdrawal space <NUM> and the outer surface of the second damper <NUM>, with the result that no separate structures, that is, the flow restrictors <NUM>, <NUM> restricting the amount of the outlet flow, <NUM>, are not necessarily needed but the small play 18a, 24a itself acts as a structure restricting the amount of the outlet flow. The structure can operate without the actual restrictors <NUM>, <NUM> also when the piston <NUM> and the piston rod <NUM> have no sliding bearings.

In the structure according to <FIG>, a separate structure <NUM>, that is, a third flow restrictor restricting the amount of the outlet flow and preferably constituted by a separate sealing ring, for example, but just as well by a short annular projection extending towards the center axis of the borehole <NUM> and having a diameter smaller than that of the rest of the borehole <NUM>, is provided on the inner surface of the borehole <NUM> of the front end <NUM>, in proximity to the front face 4a of the front end <NUM>. In this case, the projection serving as the structure <NUM> restricting the amount of the outlet flow preferably is made of the same material as the front end <NUM>. The third flow restrictor <NUM> creates a choke between the outer diameter of the piston rod <NUM> and the borehole <NUM> to restrict the air flow leaving the pressure space <NUM> and/or the second damper withdrawal space <NUM>.

However, the inner diameter of the third flow restrictor <NUM> exceeds, by a small play <NUM>, the outer diameter of the piston rod <NUM> at the borehole <NUM>. Thus, a small leakage exists in the play <NUM> between the piston rod <NUM> and the third flow restrictor <NUM>. In a solution where the flow restrictor <NUM> is a separate ring, the ring is adapted to be freely floating on the piston rod <NUM>, resulting in that the ring does not act as a bearing for the piston rod <NUM> and, therefore, does not wear out easily.

Preferably, the third flow restrictor <NUM> is adapted to also serve as wiper to wipe off any loose scrap and any material stuck to the inward moving piston rod <NUM>. The compressed air discharged from the play <NUM> is adapted to contribute to the wiping result. Preferably, the third flow restrictor <NUM> is made of metal or plastic.

<FIG> is an enlarged, simplified lateral and cross-sectional detail view of a preferable way of sealing the piston rod <NUM> of a preferred pneumatic cylinder accor ding to the invention. In this solution, the structure is similar to that of the solution shown in <FIG> but, now, the piston rod <NUM> has a sliding bearing <NUM> which here is only one in number but which also can be more in number in parallel configuration. The periphery of the sliding bearing <NUM> may comprise several portions, with gaps between the ends of these portions to allow the compressed air pressed out of the second damper withdrawal space <NUM> and into the play <NUM> to easily move forward and out of the pressure space <NUM>, from between the third flow restrictor <NUM> and the piston rod <NUM>.

In this embodiment, the third flow restrictor <NUM> is a ring inserted into an annular recess <NUM> in the end face of the front end <NUM> and axially locked in place, at its outer end face, by a lock ring <NUM> and sealed, at its end face facing the pressure space <NUM>, that is, its inner end face, by an annular sealing <NUM> spaced from the moving piston rod <NUM>. As mentioned above, said separate ring acting as the flow restrictor <NUM> is adapted to be freely floating on the piston rod <NUM>, the outer diameter of the ring being smaller, by a desired play, the inner diameter of the recess <NUM>. Thus, the piston rod <NUM> does not abrade against the third flow restrictor <NUM>, preventing both of them from wearing out and giving them a long service life. In consistent with <FIG>, the sliding bearing can be also omitted in the structure shown in <FIG>.

<FIG> is a simplified lateral and cross-sectional detail view of a prefeerable way of fastening the rear end <NUM> of the pneumatic cylinder according to the invention. The fastener <NUM> of the cylinder member is fastened to the rear end <NUM> by means of a fastening flange <NUM>, in a flexible way in order to allow for a damped movement of the fastener <NUM> by the strokes of the piston <NUM>. The fastener <NUM> is a separate element having an elastic damping ring <NUM> in its fastening hole as well as elastic damping pads <NUM> and <NUM> in the portion of the fastener enclosed by the rear end <NUM> to act in both stroke directions of the piston <NUM>. The damping pad <NUM> and the damping pad <NUM> are adapted to absorb the impact arising when the outward movement of the piston <NUM> stops and adapted to absorb the impact arising when the inward movement of the piston <NUM> stops, respectively.

The rear face of the rear end <NUM> has a cylindrical recess 2a where a flange-like extension 1a of the fastener <NUM> enclosed by the rear end <NUM> is accommodated. Correspondingly, the end face of the fastening flange <NUM> facing the rear end <NUM> has a recess whose diameter equals to that of the recess 2a and a center hole having a smaller diameter than the recess, the shaft part of the fastener <NUM>, which has a smaller diameter than the extension 1a, passing therethrough. The annular damping pad <NUM> is inserted into the recess 2a of the rear end <NUM> and into the recess of the fastening flange <NUM>, between the flange-like extension 1a and the fastening flange <NUM>, to press the fastener <NUM> towards the bottom of the recess 2a of the rear end.

Correspondingly, the end face of the fastener <NUM> facing the rear end <NUM> has a cylindrical recess 1b where the damping pad <NUM> is accommodated to press the fastener <NUM> away from the bottom of the recess 2a of the rear end. Between the end face of the fastener <NUM> facing rear end <NUM> and the bottom of the cylindrical recess 1b, an axial play is provided, the fastener <NUM> being able to move, within the limits thereof, during its damping movement, without contacting the rear end <NUM> and the fastening flange <NUM>. Preferably, the fastening flange <NUM> is attached to the rest of the cylinder structure by fasteners <NUM>, such as screws and nuts.

<FIG> is a simplified lateral and partially cross-sectional view of still another pneumatic cylinder according to the invention, with the piston rod <NUM> almost retracted. This is a very simple functional solution without any adjustments or abrasive dynamic seals on the outer periphery of the outer periphery of the piston <NUM> or on the piston rod <NUM>. In this solution, the rear end <NUM> only has a first flow channel <NUM> and a non-return valve <NUM> with its flow paths between the first flow channel <NUM> and the pressure space <NUM>, as well as a first damper withdrawal space <NUM>. Correspondingly, the front end only has a second flow channel <NUM> and a non-return valve <NUM> with its flow paths between the second flow channel <NUM> and the pressure space <NUM>, as well as a second damper withdrawal space <NUM> and a borehole <NUM> for the piston rod <NUM> to pass through. This simplified structure, where the flow into the pressure space <NUM> mainly takes place through the valves <NUM>, <NUM> and their flow paths, also allows for a quick movement of the piston <NUM>. At the beginning of the movement, there is a small flow through the plays 24a or 18a as well.

This solution differs from the above-described solutions in that the first damper <NUM> is provided on the opposite side of the piston rod <NUM>, with respect to the piston <NUM>, and in that the first damper withdrawal space <NUM> is located in the rear end <NUM>, in connection with the first flow channel <NUM>. Now, the structure restricting the amount of the flow leaving the first damper withdrawal space <NUM> during damping, that is, the first flow restrictor <NUM>, solely is constituted by the play 24a between the first damper withdrawal space <NUM> and the first damper <NUM>, but this solution may just as well include other kinds of flow restrictors <NUM> already described above.

Preferably, the structure of the second damper <NUM> and the second damper withdrawal space <NUM> with the flow restrictors and plays follows the description of the structure shown in <FIG> but it can also be similar to the structure of the solutions shown in any of the other Figures.

Besides, a difference from the above-described solutions is that, in this solution, the seal <NUM> of the piston <NUM> is not an abrasive seal on the outer periphery of the piston but the annular seal <NUM> is divided into two parts for either side of the piston <NUM>, the sealing of the piston <NUM> taking place in both extreme ends of the movement of the piston <NUM>. <FIG> shows a preferred structure where the seal <NUM> of the first side of the piston <NUM> and the seal <NUM> of the second side of the piston <NUM> are located on the front face of the piston <NUM> facing the rear end <NUM>, and, in the pressure space <NUM>, on the side of the front end <NUM> facing the pressure space <NUM>. For clarity, <FIG> only shows both the sectional surfaces of the seals <NUM> but not the hemispherical portion behind the sectional plane. The positioning of the piston seals <NUM> on the piston <NUM> could just as well be one of the following: both of them on the piston, on both front faces of the piston, or one in the front end <NUM>, as shown in <FIG>, and the other in the rear end <NUM>, or one in the rear end <NUM> and the other on the front face of the piston <NUM> facing the front end <NUM>.

The solution according to <FIG> also discloses a structure of the free end of the piston <NUM> differing from the above. However, the structure could just as well be similar to the above. The solution shown in <FIG> does not have a separate flange against the second mating surface 6c but the mating surface 6c is located on the fastener <NUM> of the piston rod <NUM>. Besides, the sealing element 6a is attached to the first mating surface 6a of the front end <NUM>. The sealing element 6a could just as well be attached to the second mating surface 6c or be a separate structure <NUM> floating on the piston rod <NUM>.

<FIG> is a simplified lateral and partially cross-sectional view of still another pneumatic cylinder according to the invention, with the piston rod <NUM> almost retracted. This solution is also free from any abrasive dynamic seals on the outer periphery of the piston <NUM> or on the piston rod <NUM>. The structure is otherwise substantially identical to the solution of <FIG> but it also shows the above-mentioned constant-flow paths and the damping flow paths, with their regulators <NUM>, <NUM>, participating in the damping of the movement of the piston <NUM>. Besides, the positioning of the annular seals <NUM> of the piston <NUM> differs from the solution of <FIG>. In the solution of <FIG>, the seals <NUM> sit in annular grooves provided in the ends of the rear end <NUM> and in the front end facing the pressure space <NUM>, the outer periphery of the seals <NUM> being located as close to the inner periphery of the pressure space <NUM> as possible or being fixed thereto. For clarity, <FIG> only shows both the sectional surfaces of the piston seals <NUM> but not the hemispherical portion behind the sectional plane.

<FIG> is a simplified lateral and partially cross-sectional view of still another pneumatic cylinder according to the invention, with the piston rod <NUM> almost retracted. This solution is also free from any abrasive dynamic seals on the outer periphery of the piston <NUM> or on the piston rod <NUM>. This structure is otherwise substantially identical to the solution of <FIG> but it discloses a different sealing structure for the piston <NUM>. The annular seals <NUM> are different and their positioning differs from the solution of <FIG>. In the solution of <FIG>, the seals <NUM>, which are substantially V-shaped in cross-section, are located on both sides of the piston <NUM>, in a groove made in the corner between the outer periphery of the piston <NUM> and each end of the piston and having a substantially V-shaped cross-sectional profile, the other branch of each seal <NUM> extending beyond the end plane of the piston <NUM>. Besides, the seals <NUM> are positioned in such a way that there is a play between them. Thus, the seals <NUM> do not abrade against the inner surface of the pressure space <NUM>, as the piston <NUM> moves, the piston <NUM> and the inner surface of the pressure space <NUM> having a play 20a between them, as the piston <NUM> moves. For clarity, <FIG> only shows both the sectional surfaces of the piston seals <NUM> but not the hemispherical portion behind the sectional plane. In the solution of <FIG>, the sealing takes place at each extreme end of the movement of the piston <NUM> by sealing the branch of the seal <NUM> extending beyond the end plane of the piston <NUM> against the end face of either the rear end <NUM> or the front end <NUM> facing the pressure space <NUM>.

Besides, the solution of <FIG> differs from the other disclosed solutions in that, now, the sealing element 6a of the sealing arrangement <NUM> is a separate structure floating on the piston rod <NUM>. The sealing element 6a could just as well be identical to any of the sealing elements 6a described above, or a different structure.

In the structure of <FIG>, the piston <NUM> is, as it is moving, spaced from the inner surface of the pressure space <NUM>, by the play 20a, the sealing of the piston <NUM> only taking place at each extreme end of the movement of the piston <NUM>. Thus, the piston <NUM> is adapted to move in the pressure space <NUM> contactlessly, the play 20a being unsealed during the movement of the piston <NUM> and, therefore, the pressure medium leaks out through the play 20a. This unsealed play 20a is advantageous for the service life of the structures because the seals <NUM> do not heat up the inner surface of the pressure space <NUM> by abrading against it. Further, these non-abrasive seals do not wear out quickly.

All of the solutions describe above, and any other solutions according to the invention as well, may preferably have said play 20a, or the like, between the piston <NUM> and the inner surface of the pressure space <NUM>, the piston <NUM> only being sealed by the seals <NUM> at the extreme ends of the movement of the piston <NUM>.

One of the main ideas with the arrangement according to the invention is to omit as many abrasive dynamic seals as possible in the structure of the pneumatic cylinder, preferably in the piston <NUM> and the piston rod <NUM>. At the same time, any frictions caused by the seals and possibly varying as the outside temperature of the cylinder changes, and as the cylinder gets older, are eliminated. Thus, less regulation is needed. In the structure of the pneumatic cylinder according to the invention, there is no seal in a sealing contact with the piston rod <NUM> between the piston rod <NUM> and the structure used for controlling the piston rod. In other words, the piston rod <NUM> is adapted to move substantially contactlessly in the borehole <NUM> of the front end <NUM>. Omitting the seals on the piston rod <NUM> results in that air leaks out of the play <NUM> between the piston rod <NUM> and the borehole <NUM> of the front end. This has an advantageous aspect in that it helps to remove any dirt stuck to the piston rod <NUM>. In the arrangement according to the invention, this leak is not blocked until at the end of the entrance movement of the piston rod <NUM>, by an elastic seal 6a having a long service life due to not being subjected to an abrasive movement, unlike the prior-art piston rod seals.

Preferably, the piston <NUM> is adapted to move substantially contactlessly in the pressure space <NUM> and the sealing of the piston <NUM> only takes place at the extremes of the movement of the piston <NUM>.

In the arrangement according to the invention, the adjustment of the damping of the movement of the piston <NUM> at the end of the movement of the piston <NUM> is carried out by using a spring-loaded pressure restricting valve, that is, the above-mentioned damping regulator <NUM>, <NUM> regulating the maximum pressure of the air flow leaving at the damping step. This means that, in the arrangement according to the invention, the damping is regulated by regulating the maximum pressure of the air flow while the prior-art solutions generally adjust the size of the flow orifice, that is, the flow itself.

In the arrangement according to the invention, the movement of the piston <NUM> is controlled by using one or more valves allowing pressure to be charged into and discharged out of the pressure space <NUM> of the cylinder. A preferable solution uses a <NUM>/<NUM> valve. In this case, pressure is alternately introduced into the second flow channel <NUM> of the front end <NUM> and the first flow channel <NUM> of the rear end <NUM>, both of them branching into two separate flow paths.

The first branching flow path of the rear end <NUM> comprises a non-return valve <NUM> delivering pressure into the pressure space <NUM>. The second branch of the first flow channel of the rear end <NUM> also continues into the pressure space <NUM>, through the central channel 16a of the damper <NUM>. The constant-orifice constant-flow path 14b connecting to the pressure space <NUM>, and the damping regulating flow path 14a, comprising the maximum damping pressure regulator <NUM>, such as a control valve, also join this second branch of the first flow channel.

As a gaseous pressure medium, such as air, is led, through the first flow channel <NUM> of the rear end <NUM>, into the pressure space <NUM> of the cylinder, a small amount of the medium also travels through both the constant-flow path 14b and the play 24a of the first damper <NUM>. After the piston <NUM> of the cylinder has moved over a distance, the central channel 16a extending through the space of the first damper <NUM> and acting as a flow path becomes entirely open. As the piston <NUM> moves backwards and the second flow channel <NUM> is pressurized, the pressure is initially discharged through the central channel 16a of the damper <NUM>, without any limits, until the damper <NUM> limits the flow, resulting in that, at the same time, a small amount of pressure also is discharged through the constant-flow path 14b. After the first damper <NUM> has limited the flow, the pressure starts to rise in the pressure space <NUM>. Once the pressure prevailing in the pressure space <NUM> has risen to a desired level, the pressure regulating valve of the regulator <NUM> opens and the pressure medium flow is able to travel to the first flow channel <NUM> of the rear end <NUM> and, therefrom, out of the system, through the control valve. The elevated pressure of the pressure space <NUM> between the piston <NUM> and the rear end <NUM> limits the movement of the piston, and consequently, also that of the mass moved the pneumatic cylinder, such as the blade of a circular saw, suitably preventing any mechanical stress at the end of the stroke.

Correspondingly, the first branching flow path of the front end <NUM> comprises a non-return valve <NUM> delivering pressure into the pressure space <NUM>. The second branch of the second flow path <NUM> of the front end <NUM> also continues into the pressure space <NUM>, through the second damper withdrawal space <NUM>. The constant-orifice constant-flow path 15b connecting to the pressure space <NUM> of the cylinder, and the damping regulating flow path 15a comprising the maximum damping pressure regulator <NUM>, such as a control valve, also join the second branch of the second flow path <NUM>. The operation of the non-return valve <NUM> of the front end <NUM>, and of the flow paths thereof, and of the structures <NUM>, 15a, 15b, <NUM>, 18a and <NUM> damping the movement of the reciprocating movement of the piston <NUM> at the extreme ends of the movement, is substantially similar to that of the above-described corresponding structures of the rear end <NUM>.

The simplified structure shown in <FIG> and <FIG> includes neither the above-mentioned flow paths 14a, 14b, 15a and 15b nor the control valves <NUM>, <NUM>. Therefore, at the beginning of the movement of the piston <NUM>, the pressure medium of the first flow path <NUM> in the front end <NUM> travels into the pressure space <NUM> of the cylinder through the first non-return valve <NUM> and the flow path thereof. Besides, a small amount of the pressure medium may also travel through the play 24a of the first damper <NUM>.

Correspondingly, in structure shown in <FIG> and <FIG>, the pressure of the second flow channel <NUM> in the front end <NUM> is discharged, the at the beginning of the minus stroke of the piston <NUM>, into the pressure space <NUM>, through the second non-return valve <NUM> and the flow path thereof. At the same time, a small amount of the pressure medium is also discharged through the play 18a of the second damper withdrawal space <NUM>. Once the distance of the movement of the piston <NUM> towards the rear end <NUM> has caused the second damper <NUM> to come out of the second damper withdrawal space <NUM>, pressure is freely discharged into the pressure space <NUM>, through the second damper withdrawal space <NUM>.

It will be appreciated by a person skilled in the art that the different embodiments of the invention are not restricted to the examples above but may vary within the scope of the following claims. Hence, the structure of the pneumatic cylinder, including the ends, pressure space, piston, flow paths, dampers, seals and regulators, may differ from the above. Likewise, it is also possible to add any of the alternative above-mentioned structures to the structure, in a variety of suitable ways.

Claim 1:
An arrangement comprising a pneumatic cylinder, the pneumatic cylinder having a rear end (<NUM>), a front end (<NUM>) and a pressure space (<NUM>) therebetween, the pressure space (<NUM>) containing a piston (<NUM>) reciprocating in the pressure space (<NUM>) and having a piston rod (<NUM>) whose free end is arranged to project, through a guiding structure (<NUM>) provided in the front end (<NUM>) and guiding the piston rod (<NUM>), out of the pressure space (<NUM>), wherein a play (<NUM>) is provided between the guiding structure (<NUM>) and the piston rod (<NUM>) to conduct the pressure medium out of the pressure space (<NUM>) during the movement of the piston rod (<NUM>), the pneumatic cylinder further comprising a first pressure medium flow channel (<NUM>) leading to a first side of the piston (<NUM>) and a second pressure medium flow channel (<NUM>) leading to a second side of the piston (<NUM>), as well as structures damping the reciprocating movement of the piston (<NUM>) at the extreme ends of the movement, including at least a first damper (<NUM>) and a second damper (<NUM>), and the structures damping the reciprocating movement of the piston (<NUM>) at the extreme ends of the movement comprise a first structure (<NUM>) restricting the amount of flow leaving during the damping and a second structure (<NUM>) restricting the amount of flow leaving during the damping, wherein the pneumatic cylinder has a sealing arrangement (<NUM>) adapted to seal against a pressure medium flow out of the pneumatic cylinder, through the play (<NUM>) as the piston (<NUM>) and the load moved by it are in the retracted extreme position, wherein the sealing arrangement (<NUM>) comprises a first matching surface (6b) on the front end (<NUM>), a second matching surface (6c) moving along with the piston rod (<NUM>) and an elastic sealing element (6a) between the matching surfaces, wherein the sealing element (6a) is adapted to be pressed between the matching surfaces (6b and 6c) as the piston rod (<NUM>) is in its retracted extreme position, characterized in that the first matching surface (6b) is located on the front face of the front end (<NUM>).