PRESSURE FOOT ASSEMBLY

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates a pressure foot assembly adapted to be detachably mounted to a wrist of a manipulator's arm and to carry thereon an axially movable orbital drilling machine used for producing holes in material structures requiring high accuracy tolerances and surface smoothness, such as fiber-reinforced composite materials and laminates. More particularly, such a pressure foot assembly is primarily used to press an outer material layer, e.g. a sheet or panel, against an inner material layer, e.g. a supporting structure, sufficiently hard, so that no burrs or de- lamination will occur anywhere along the extent of the hole and that no chips or de- bris will enter the interface between the material layers. This orbital drilling technology is commonly practiced in the space and aircraft industries.

2. Description of related art

Orbital drilling machines are previously known; cf. e.g. US 6,663,327 B2, and

US 6,719,505 B2, the contents of which are incorporated herein by reference. Such orbital machining devices are usually constructed as hand held or portable tool apparatuses which are especially suitable for drilling holes and/or recesses in work- pieces comprising fiber-reinforced composite materials and laminates, wherein the drilling unit in itself provides for an orbital movement of a cutting tool which is positively governed by the an integrated excenter mechanism of a spindle unit.

When using such an orbital drilling machine attached to a wrist of a manipulator's arm for producing holes in two or more adjacent material layers, a so called pres- sure foot on a bracket carrying the drilling machine is displaced against the outer

material layer to apply a sufficient pressure thereon to eliminate the chance of introduction of delamination of and/or chips into the interface between the material layers. The pressure foot has an aperture which is penetrated by the cutting tool of the drilling machine during the axial feed of the cutting tool into the workpiece by slid- ing the drilling machine along guide rails on the bracket. The pressure foot is connected to an actuator which is able to displace it axially towards the outer material layer so as to apply a sufficiently high pressure thereto. However, the resulting force generated by the actuator acts on the pressure foot from a radially offset position relative to center of the aperture. This requires high forces to achieve sufficient pressure to the material layers and may create a bending torque on the part of the bracket having the guide rails, resulting in curved guide rails, which may cause a misalignment of the longitudinal center axis of the cutting tool with a predetermined normal to the workpiece surface where the hole is to be drilled. Therefore, sensors and adjusting members are needed to compensate for such high bending torques.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved pressure foot assembly which eliminates the above-mentioned drawbacks and requires less forces to ob- tain sufficient pressure on the material layers. To this end the pressure foot assembly of the invention is characterized by the features of claim 1. This will minimize the necessary force to be applied by the force actuator for sufficiently compressing the material layers and eliminates the creation of a torque adversely bending the bracket frame carrying the orbital drilling machine thereby preventing the guide rails from being curved and thus obviating a misalignment of the cutting tool with a normal to the surface at which a hole is to be drilled.

Further structural details of the pressure foot assembly of the present invention are defined in the dependent claims and will be apparent from the accompanying draw- ings and the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic perspective view of an orbital drilling machine with a pressure foot assembly adapted to be detachably mounted to a wrist of a manipulator's arm;

Fig. 2 is a side view of the assembly in Fig. 1 with the drilling machine in a retracted position;

Fig. 3 is a schematic perspective view of the pressure foot assembly and a force- transmitting unit thereof;

Fig. 4 is a perspective view of the pressure foot assembly similar to Fig. 1 but without a drilling machine mounted thereto; and

Fig. 5 is a side view of the arrangement in Fig. 4 without guide rails and slide mem- bers for the pressure foot member and the drilling machine.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In Fig. 1 10 generally denotes an orbital drilling machine which is slideably mounted to a bracket 12 configured to be detachably mounted to a wrist of a manipulator's arm (not shown). The orbital drilling machine 10 may be of the kind disclosed in the U.S. Patent No. 6.663,327 B2. The bracket 12 is provided with a circular mounting plate 14 for the attachment of the bracket 12 to the robotic wrist, and a cantilevered frame part 16 extending perpendicularly from the mounting plate 14 and provided with parallel guide rails 18 on the upper side thereof for linearly guiding the drilling machine 10 thereon by means of four slide members 20 and an axial feed mechanism (not shown).

A pressure foot member 22, configured for pressing and holding an outer material layer, e.g. a flat or curved sheet or panel of an aircraft, against an inner material layer, e.g. a supporting structure, with a sufficient force for avoiding introduction of

delamination of and/or chips into the interface between the outer and inner materials when drilling a hole therethrough, is slideably mounted to a distal portion of the guide rails 18 by means of respective slide members 24 and a force actuator 26 which is disclosed more clearly in Fig. 3. The pressure foot member 22 has an aper- ture 28 through which the cutting tool 30 (Fig. 2) of the drilling machine 10 can pass into the workpiece (material layers) in order to produce a hole and/or a recess (countersink) therein.

As shown in Fig. 3, the force actuator 26 may comprise two parallel pneumatic cyl- inders 32 pivotally attached at 33 to the frame part 16 of the bracket 12, and the piston rods 34 of which are pivotally connected to a lower end of a respective one of two parallel double-armed levers 36 which are rotatable about a shaft 38 mounted to the bracket 12. Of course, the force actuator 26 may also consist of any suitable electric or hydraulic drive unit. The upper end of the respective double-armed levers 36 is pivotally connected at 40 to a force-transmitting unit 42 for transmitting a pressure force to the pressure foot member 22 so as to apply a desired pressure to the outer material layer against the inner supporting structure. The force-transmitting unit 42 comprises two parallel push bars 44 with angled rear end portions 46 pivotally connected to the double-armed levers 36, and raised front portions 48 piv- otally connected to the pressure foot 22 at 50.

As shown best in Fig. 5, according to the present invention, the point 40 of pivotal connection of the force-transmitting unit 42 to the double-armed levers 36, is levelled or aligned with the point 50 of connection of the force-transmitting unit 42 to the pressure foot member 22 as well as substantially levelled and concentrically aligned with the longitudinal center axis of the cutting tool 30 and the aperture 28 (Fig. 2). This will prevent generation of a torque causing a bending of the bracket frame part 16 when applying an axially directed force to the force-transmitting unit 42 at the pivot point 40 by swinging the levers 36 in a counter-clockwise direction, as seen in the drawings, about the shaft 38 by means of the pneumatic cylinders 32 and the piston rods 34. The manipulator is controlled to bring the pressure foot

member 22 to engage the outer surface of the workpiece with a sufficient force in a direction substantially normal to the surface. This will create provision of a reference position for carrying out a countersink to a predetermined depth and will minimize the necessary force to be applied by the force actuator 26 for sufficiently com- pressing the material layers to prevent delamination and introduction of chips into the interface between the material layers.

The pressure foot assembly of the present invention is not limited to the embodiment described above but could be modified within the scope of the following claims.