Collision sensing device

The invention relates to a collision sensing device which can detect a collision between two or more objects. The collision sensing device comprises a deformable member (5) that defines a space (15) which can be assigned a pressure. In a first condition, the deformable member is undeformed, whereby the space (15) is assigned a first pressure (P1). In a second condition, the deformable member (5) is deformed whereby the space (15) is assigned a second pressure (P2). The pressure in the space is monitored. A collision with an object is detected when the pressure in the space changes from the first pressure to the second pressure.The invention can e.g. be applied in connection with machining, such as water jet cutting, but several other fields of application are also conceivable.

FIELD OF INVENTION

The invention relates to a collision sensing device, which is adapted to detect a collision between two or more objects. The invention also relates to an apparatus for machining that comprises said collision sensing device.

In many situations, it is desirable to detect a collision between objects. One purpose can be avoiding collisions. The invention is directed towards detecting a collision between a tool and an obstacle in a workpiece during machining. Machining is here intended to in particular comprise all sorts of cutting machining such as water jet cutting, gas cutting, plasma cutting, laser cutting et cetera. During the machining it can on the one hand be desired to protect the tool, e.g. a nozzle of some kind, from damage due to a collision with an obstacle such as an unevenness in the workpiece. On the other hand, it can be desired to protect parts of the workpiece from damage due to collisions with a tool. The invention can also used in other situations, such as vehicles, in particular in connection with parking of vehicles.

A traditional way of protecting objects is to provide them with a shock absorbing protection of flexible material.

In U.S. Pat. No. 5,366,156 A is described how an object is cleaned by means of an aerosol which is directed at the surface of the object by a nozzle202. The nozzle is provided with a protecting coating265(FIG. 8) in order to protect the object against damage by accidental contact with the nozzle. Such a coating can only provide a limited protection. In case the nozzle is guided with great force, for instance, there is a risk that the nozzle is bent as a result of collision with an object. Also the object may be may be damaged. Further, U.S. Pat. No. 5,366,156 A does not provide for a detection of the collision.

On vehicles, such as cars, bumpers provide a corresponding protection. When it comes to vehicles, collisions can also be avoided by means of more sophisticated equipment, such as so called backup sensors that alert when obstacles approach. Here, use is made of ultrasound which is reflected against the obstacle. A technique of this kind is relatively expensive. Further, a plurality of sensors must be installed in order to protect an object in all directions. Moreover, the sensors are sensitive to dirt, humidity and mechanical influences.

In connection with machining, collision sensing devises incorporating electrical switches that signal collisions have been put to use. However, this solution has not led to satisfying results. This is partly because these collisions sensing devises often have been damaged due to mechanical influences, and partly because they have been expensive owing to a relatively complex design construction.

Thus, there is a need for a collision sensing device that is reliable, has a relatively simple construction, can endure dirt and mechanical influences, and is independent of the form of the obstacle.

SUMMARY OF THE INVENTION

The present invention relates to a collision sensing device, such as may be used in a water jet cutting apparatus, which can detect a collision between two or more objects. The collision sensing device comprises a deformable member which defines a space that can be assigned a pressure. In a first condition, the deformable member is undeformed whereby the space is assigned a first pressure. In a second condition, the deformable member is deformed whereby the space is assigned a second pressure. Upon collision of the deformable member with an object, the deformable member is deformed into the second condition, whereby the pressure in the space changes from the first pressure to the second pressure. The collision sensing means further comprises a means for detecting the pressure change. The first pressure is preferably an overpressure. Thereby is prevented that dirt or other unwanted material enters the space. The second pressure is lower than the first pressure. The collision sensing device can also include a pressure generator for providing the space said overpressure through an opening in the boundary surface of the space.

In the first condition, i.e. when the deformable member is undeformed, the space is preferably closed. After the deformation of the deformable member, i.e. to the second condition, the space is preferably not closed. As a consequence, the second pressure will be closer to the ambient pressure than is the first pressure.

The deformable member may be configured as a splatter shield which has the form of a frustum of a cone with circular cross-section. The cone is arranged with its wider end towards a workpiece. Hereby a relatively large detection or sensing area is obtained, within which a collision with one or more objects is detected. The splatter shield can also take other forms. The splatter shield can e.g. be of rectangular cross-section, or be tubular. The space that is assigned the pressure is defined by the upper side of the splatter shield, a bulge enclosing the upper side of the splatter shield and also a support plate which is sealingly arranged against the bulge. In this manner, a collision sensing device of simple construction in achieved.

The invention further relates to an apparatus for machining where the apparatus comprises said collision sensing device. The machining is preferably water jet cutting.

DETAILED DESCRIPTION OF THE INVENTION

Below, an embodiment of the invention is described with reference to the enclosed figures. The embodiment merely serves as an example of an application of the invention, and is not intended to limit the claimed scope, which is defined by the independent claims.

A preferred embodiment of the invention is shown inFIG. 1, where the collision sensing devise is adapted for use in water jet cutting. In this apparatus for water jet cutting a splatter shield5is utilized as deformable member, which encloses a nozzle6for water jet cutting. The splatter shield5comprises a side wall and an upper part. The side wall of the splatter shield5is formed as a frustum of a cone, se alsoFIGS. 2 and 3. The cone has a wider end and a narrower end. The wider end, which is turned downwards in the figures, is open and is during machining located just above the surface of the workpiece2. The edge11of the wider end is located closer to the surface of the workpiece2than is the end of the nozzle6, or, the edge11of the wider end is located at the same distance from the surface of the workpiece as is the end of the nozzle6. The narrower end, i.e. the upper part20of the splatter shield that is turned upwards in the figures, is closed with exception for a central opening10which is intended for the water jet cutting nozzle6(below referred to as “nozzle”).

During the water jet cutting the splatter shield5is arranged around the nozzle6and retained in an appropriate manner, e.g. by force fit. The diameter of the central opening10is then made somewhat smaller than the diameter of the nozzle6. The primary task of the splatter shield is to hinder material and water splatter from the machining process. The splatter shield is manufactured from a soft flexible material, such as rubber with a Shore hardness within the range 75-95, preferably the Shore hardness is within the range 85-95, more preferably the Shore hardness is around 90.

FIG. 2shows a perspective view of the splatter shield5as viewed at an angle from the workpiece2. The splatter shield5has a notch8in the side wall21, through which notch8an arm9for height adjustment extends. During operation, the arm9for height adjustment holds a measurement device (not shown), which measures the distance from the nozzle6and the workpiece2. The present invention also functions without said notch8and said arm9for height adjustment, respectively.

The upper side16of the splatter shield5, i.e. the closed and away from the workpiece2turned end of the cone, is enclosed by a protruding edge or bulge12, see in particularFIG. 3. An essentially circular support plate7is arranged against the bulge12, whereby the under side19of the support plate7bears against the upper side of the bulge12. Since the splatter shield5is made from a soft elastic material, the bulge12lies sealingly against the support plate7. The support plate is preferably manufactured from a form stable material, e.g. metal or plastic. The support plate shall be of such form and size that it seals against the bulge in the undeformed condition of the splatter shield.

The nozzle6passes through the support plate7and the splatter shield5. The central opening10in the upper part20of the splatter shield5, through which the nozzle6passes, has a slightly smaller diameter than has the nozzle6, so that the splatter shield5seals against the nozzle6. Also the support plate7is furnished with a central opening14, through which the nozzle6passes. This opening14is adjusted for the diameter of the nozzle6, it is also feasible to arrange a suitable sealing between the central opening14of the support plate7and the nozzle6, e.g. in the form of one or more O-rings (not shown). Consequently, an essentially closed space15is defined by a boundary surface which is formed by the upper side16of the splatter shield5, the inner side of the bulge12of the splatter shield, the under side19of the support plate7, and also the nozzle6and any sealings arranged around this.

The support plate is preferably fixed to the splatter shield, which, in turn, is fixed to the nozzle5. InFIG. 3is schematically shown how the support plate7is fixed to the splatter shield5by means of an attachment means18, which extends through the upper part20of the splatter shield and into an opening17in the support plate. The attachment means18can e.g. be a screw or a bolt, in which case the opening17is provided with an inner thread. In order to make sure that the bulge12bears sealingly against the under side19of the support plate with an even contact pressure along the entire circumference of the bulge, as seen in a plane parallel to the upper part20of the splatter shield, a number of attachment devices18are preferably arranged. The attachment means18are preferably arranged at even intervals along the circumference of the splatter shield and the support plate. For example, three attachment means devices18at a mutual distance of 120° in a plane parallel to the upper part20of the splatter shield can be put to use. In order to achieve a yet more even contact pressure between the bulge12and the under side19of the support plate, a larger number of attachment devices18can be used.

For reasons that will be clear below, such attachment device18should not be arranged at the very outer circumference of the upper part20of the splatter shield5. Such placement of the attachment device18would impede the deformation of the splatter shield5.

Alternatively, the support plate7can be attached to the nozzle6by a fixing element. Such fixing element includes e.g. adhesive or screw connection.

In order to achieve the essentially closed space described above, other designs of the splatter shield and the support plate are conceivable. For instance, the upper side of the splatter shield may be flat, and a bulge facing the splatter shield may be formed on the support plate. Alternatively, a separate sealing element, such as an O-ring or a gasket, may be arranged between the support plate and the upper side of the splatter shield.

InFIG. 1the apparatus for water jet cutting with the collision sensing device is shown in its entirety. The support plate7comprises an opening13for air supply. This opening13can e.g. be formed as an internally threaded hole. To the opening13a conduit4is connected, through which the spacing is provided with a gas, preferably air. The air is provided from a pressure generator (not shown), such as a compressor, as is indicated by the arrow1inFIG. 1. The pressure in the conduit4is monitored by a pressure monitor3. In this way the space15, which is defined by the splatter shield5and the support plate7, can be assigned a monitored static overpressure i.e. a pressure exceeding the ambient pressure. This overpressure thus corresponds to the pressure in the conduit4. At normal operation the space15is supplied with air through the conduit4, whereby a first pressure P1prevails in the space15. Thus, the pressure P1exceeds the ambient pressure. The overpressure P1in the space15lies within the range 0.1-2 bar, preferably the overpressure P1lies within the range 0.2-1.5 bar, most preferred is an overpressure of 0.3-0.8 bar.

Alternatively, the pressure generator and the pressure monitor can be connected to the support plate7via separate conduits or hoses. The support plate7is then modified so as to comprise an opening for supply of air, or another gas, and one opening for pressure measurement. The pressure measurement device can also, instead of being connected via a conduit, be arranged directly on the support plate7.

During the water jet cutting, the nozzle6which is furnished with the splatter shield5is driven along the along the workpiece2to be machined, or the workpiece2is moved while the nozzle6with its splatter shield5is kept still. This movement of the nozzle6or the workpiece2is normally performed mechanically following a programmed path. In case an object or an unevenness, which protrudes from the surface of the workpiece2, is located in or close to the intended path of the nozzle6, the splatter shield5, due to the relative movement, will contact this object. Then, due to the relative movement, the splatter shield5will deform elastically. Typically, this deformation will imply that the side wall21of the splatter shield5is pushed in, in a direction essentially perpendicular to the longitudinal axis of the nozzle6, towards the centre of the frustum of a cone. This impression will cause a displacement of the bulge12of the splatter shield, so that the sealing contact with the support plate7is broken. Typically, the bulge12is displaced downwards inFIG. 1, i.e. towards the surface of the workpiece2. As the bulge12no longer bears against the support plate7, the space15is no longer closed. Now, the air that is supplied to the space15via the conduit4can flow out through the opening which is formed in the boundary surface of the space15upon the deformation of the splatter shield5, whereby the pressure in the space15falls to a second pressure P2. The pressure P2is thereby lower than the pressure P1, and more precisely the pressure P2lies between the ambient pressure and the pressure P1, depending on how much the splatter shield5is deformed upon the collision with the object, as explained below. Preferably the overpressure P2amounts to about half of the overpressure P1. The pressure change within the space can be detected by the pressure measurement device3. Preferably, the pressure measurement device3thereby can emit a stop signal which interrupts the mechanical movement of the nozzle6or the workpiece2. In this manner a collision between the nozzle6and the object is avoided.

Depending on how fast the movement is interrupted, and which speed the relative movement has, the splatter shield5is deformed to a different extent at the contact with an obstacle. If the speed of the relative movement, i.e. the cutting speed, is low and if the movement is interrupted immediately at the smallest change from the pressure P1within the space15, the bulge12of the splatter shield5will only be displaced a short distance from the support plate7on collision with an obstacle. In this case, only a small deformation of the splatter shield5is allowed and a relatively large remaining distance between the nozzle6and the obstacle is ensured. Now, the second pressure P2will be relatively close to the first pressure P1. By defining in advance the change of pressure to be required by the pressure measurement device in order to emit a stop signal, the distance at which the nozzle6shall stop from an imaginary obstacle can be preset.

Thus, with the present arrangement of the deformable member5, a collision, or a contact with an obstacle, is detected well before the object to be protected, here the nozzle6, collides with the obstacle. In other words, it is the deformable member5that is subject to the collision.

Since the pressure measurement device3detects a pressure change, from P1to P2, upon the splatter shields5collision with an object the space15need not be completely airtight. The space15can be continuously supplied with air, or another gas, from the pressure generator. If the space15is not completely airtight, but comprises one or more openings in the boundary surface, the supplied air will continuously leak out. Nonetheless, a first pressure, P1, will prevail in the space which pressure upon deformation of the splatter shield5, and upon subsequent displacement of the bulge12from the support plate7, will decrease to a second pressure, P2.

Preferably, as mentioned, said pressure generator gives rise to an overpressure, P1, within the space15. The advantage of keeping an overpressure in the space15is that neither dirt nor other unwanted material can enter the space15or the pressure generating device or the pressure measurement device3. However, the invention also functions if the pressure generator gives rise to an underpressure. Upon collision and transition to the second pressure, P2, ambient air would flow into the space15, and the second pressure, P2, would consequently be higher than the first pressure, P1. An advantage of assigning the space15an underpressure is that the underpressure contributes to keeping the space15tight, in that the underpressure acts on the elastic splatter shield whereby the bulge12is pressed against the support plate7.

The principle of the invention, to assign an essentially closed space a pressure which is monitored and which is changed as the boundary surface of the space is opened in connection with a deformation of an elastic member due to a contact between two objects, can be put to use in several situations. For instance, such a space could be defined by a relatively soft elastic part of a vehicle bumper. A driver could in this manner be notified upon collision with another object.

When choosing material for the deformable member, the collision force and the sizes of the constituents must be carefully considered, so that the material is sufficiently compliant for the closed pressurized space to open upon a collision, but at the same time rigid enough to resist opening during operation due to other parameters. Examples of such parameters, when the collision sensing device is used in connection with water jet cutting, are acceleration upon change of cutting speed, the presence of loose objects such as grains of sand on the surface of the workpiece, the overpressure within the space, air pressure generated by the cutting beam, material and water splatter from the cutting process et cetera.