Cutting apparatus and drive assembly

A method for controlling axial movement of a cutting head of a boring apparatus whilst the cutting head is rotating at a cutting rotation velocity ω1, the method comprising:

• providing a boring apparatus including:
• a feed screw mounted to rotate about its axis having a first planetary gear assembly at its proximal end,
• a cutting head and boring bar coaxially mounted on the feed screw by a feed nut whereby rotation of the feed nut by one full rotation relative to the feed screw causes movement of the cutting head by a distance P along the axis,
• a tubular drive shaft coaxially mounted around the boring bar, operably connected to the boring bar to rotate the boring bar about its axis and to permit relative axial movement between the boring bar and the tubular driveshaft, and having a second planetary gear assembly at its proximal end, situated adjacent to and distally situated with respect to the first planetary gear assembly,
• a drive motor operably connected to rotate the tubular drive shaft, boring bar and cutting head at a cutting rotation velocity, from zero up to a maximum cutting rotation velocity, about the axis,
• carriers of the planetary gears of the first and second planetary gear assemblies, which are rigidly interconnected, whereby the carriers rotate in unison about the axis,
• a primary feed motor arranged to drive a primary feed drive shaft operably geared to a face of a ring gear of one of the planetary gear assemblies whereby that planetary gear assembly is rotatably drivable by the primary feed motor to act as a primary feed planetary gear assembly, and wherein the ring gear of the other planetary gear assembly is arrangeable to be held with zero rotational speed or to be independently rotatable about the axis;
• operating the primary feed drive motor to drive the primary feed drive shaft at rotation velocity ω2 with the ring gear of the other planetary gear assembly held with rotation velocity zero,
• whereby the feed screw is driven through the first and second planetary gear assemblies at a rotation velocity (ω1+k·ω2) wherein k is a gear ratio, whereby the relative rotational velocity between the feed screw and the feed nut of the boring bar is k·ω2, causing the boring bar to move axially along the feed screw at a rate P·k·ω2.

A method for controlling axial movement of a cutting head of a boring apparatus whilst the cutting head is rotating at a cutting rotation velocity the method comprising:

• providing a boring apparatus including:
• a feed screw mounted to rotate about its axis having a first planetary gear assembly at its proximal end,
• a cutting head and boring bar coaxially mounted on the feed screw by a feed nut whereby rotation of the feed nut by one full rotation relative to the feed screw causes movement of the cutting head by a distance P along the axis,
• a tubular drive shaft coaxially mounted around the boring bar, operably connected to the boring bar to rotate the boring bar about its axis and to permit relative axial movement between the boring bar and the tubular driveshaft, and having a second planetary gear assembly at its proximal end, situated adjacent to and distally situated with respect to the first planetary gear assembly,
• a drive motor operably connected to rotate the tubular drive shaft, boring bar and cutting head at a cutting rotation velocity, from zero up to a maximum cutting rotation velocity, about the axis,
• carriers of the planetary gears of the first and second planetary gear assemblies, which are rigidly interconnected, whereby the carriers rotate in unison about the axis,
• a primary feed motor arranged to drive a primary feed drive shaft operably geared to a face of a ring gear of one of the planetary gear assemblies whereby that planetary gear assembly is rotatably drivable by the primary feed motor to act as a primary feed planetary gear assembly, and wherein the ring gear of the other planetary gear assembly is arrangeable to be held with zero rotational speed or to be independently rotatable about the axis;
• a secondary feed motor arranged to drive a secondary feed drive shaft operably geared to a face of the ring gear of the other planetary gear assembly whereby the other planetary gear assembly is rotatably drivable by the secondary feed motor to act as a secondary feed planetary gear assembly;
• operating the primary feed drive motor to drive the primary feed drive shaft at rotation velocity ω2,
• operating the secondary feed drive motor to drive the secondary feed drive shaft at rotation velocity ω3,
• whereby the feed screw is driven through the first and second planetary gear assemblies at a rotation velocity ω1+k·ω2−k′·ω3 wherein k and k′ are gear ratios,
• whereby the relative rotational velocity between the feed screw and the feed nut of the boring bar is k·ω2−k′ω3, causing the boring bar to move axially along the feed screw at a rate P·(k·ω2−k′·ω3).