Gear cutting – milling – or planing – Milling – With regulation of operation by templet – card – or other...
Reexamination Certificate
2002-02-26
2004-12-21
Cadugan, Erica (Department: 3722)
Gear cutting, milling, or planing
Milling
With regulation of operation by templet, card, or other...
C409S080000, C409S132000, C700S187000, C700S188000, C700S189000, C700S193000, C700S184000
Reexamination Certificate
active
06832876
ABSTRACT:
This invention relates to an improved machine tool, and improved methods of running a machine tool.
Machine tools can be used to fashion objects from blocks of material by removing excess material in a predetermined manner to arrive at the desired shape. This fashioning generally involves two processes: bulk material removal, or roughing, and fine working of the object. Bulk material removal is designed to remove excess material as quickly and as efficiently as possible to allow the fine working of the object to take place. Fine working of the object is a much finer process in which material removal is slower, more precise, and consequently the surface finish is higher.
To allow material to be removed a path must be planned for the material-remover of the machine tool. Traditionally this was performed by the manual control of a skilled operator. In the last few decades computer numerically controlled (CC) machine tools have become widespread and a set of instructions, or computer program, is used to control the path of the material-remover of the machine tool in such machines.
The set of instructions governing the path determines the efficiency of the bulk material removal process. It is desired to remove as much material in as little time as possible, but it is imperative that the material from which the object will be fashioned is not damaged.
Various material removal methods are well known and
FIGS. 1 and 2
show examples of two such methods.
FIG. 1
shows perhaps the simplest approach in which material
1
around the object
2
is removed by raster scanning the machine tool. In each pass of the machine tool the material-remover will remove an amount of material
1
, and the line
4
within the material
1
shows the centre line of each cut. It will be appreciated that this method is inefficient since the cutting tip does not run continuously, but must be stopped and moved around the object
2
in order to complete the cut on the opposite side of the object.
FIG. 2
shows another prior art method of performing the bulk material removal. Again, the line within the material
1
shows the path, or the centre line of a cut, performed by the cutting tip. The cutting tip makes a series of passes through the material
1
until only the object
2
remains.
However, none of the prior art methods discussed herein remove bulk material as efficiently as may be desired.
It is an object of the invention to ameliorate the problems of the prior art.
According to a first aspect of the invention there is provided a machine tool having a material-remover, the material-remover being able to move in at least two degrees of freedom and at a particular instant being arranged to remove an amount of material from material that it is processing, movement of said material-remover being under the control of processing circuitry, said processing circuitry determining a path along which the material-remover should move, and in determining said path allows the depth of a cut made by the material-remover to vary.
An advantage of such a machine is that it is likely to be more efficient than bulk material removal than prior art machine tools. Prior art machines are arranged to determine the path of a machine tool around the object such that the material-remover was constrained to remove roughly constant amount of material at any particular instant.
Prior art cutting machines remove slices of constant width from the material until the material has been removed as desired. This is as discussed in relation to
FIGS. 1 and 2
above. The applicants have realised that the prior art machines are sub-optimal because the amount of material removed on each cut is constant and that therefore, the solution for the optimum material-remover path is over constrained.
The machine tool may be any one of the following machines: a milling machine; a machining centre, a multi-axis machining centre, a lathe.
Conveniently, the material-remover of the machine tool is arranged to rotate about an axis. Such an arrangement is convenient because it facilitates material removal.
Preferably, the processing circuitry is arranged to attempt to move the material-remover such that the magnitude of its velocity is roughly constant. Such an arrangement is advantageous because it is more efficient to run a machine tool at its maximum cutting speed rather than continuously accelerating and decelerating the material-remover and can result in an improved life of the material remover.
However, the processing circuitry may be arranged to vary the speed of the material-remover for some complex cutting paths. It will be appreciated that the path of the material-remover will have a minimum cutting radius, which is a function of the speed of the material-remover and determined by the maximum axis acceleration of the machine.
Therefore, the processing circuitry may be arranged to reduce the speed of the material-remover in order to achieve smaller cutting radii than are possible at the target material-remover speed.
A material-remover has a maximum amount of material that it can remove in a single cut. The minimum amount of material that it can remove in a single cut is zero. The processing circuitry may comprise a track planner arranged to associate one or more tracks around the perimeter of an object to be machined, the or each track comprising a locus of all the possible material remover paths around the object. An advantage of such a track is that it provides a convenient starting point from which to calculate a material-remover path.
Alternatively, or additionally, the processing circuitry may comprise a track planner arranged to associate one or more contours around the perimeter of an object to be machined. In such an embodiment it is preferred to select a contour comprising the centre line of the track (although any value of contour between the zero and the maximum depth of cut is possible).
Conveniently, the track planner is arranged to associate a series of such tracks and/or contours around the perimeter of the object to be fabricated. As such, a series of tracks and/or contours are built up, each providing an indication of possible material-remover paths. Of course, whilst the first track and/or contour is based upon the perimeter of the object to be fabricated, subsequent tracks and /or contours are based upon the previous track and/or contour.
The track planner may produce tracks that are of variable width.
The processing circuitry may further comprise a node associator arranged to associate a number of nodes with predetermined points around the track and/or contour that has been calculated.
Preferably, the node associator is arranged to associate points with corners of the track and/or contour. A corner in the track and/or contour may be defined as any deviation in the track/contour from a straight line that results in a turn tighter than the minimum cutting radius of the material remover. Therefore, if the track/contour incorporates a curve having a radius greater than the minimum turning radius of the material remover no node may be associated therewith.
The node associator may be arranged to associate predetermined nodes with the inside of the track. Additionally the node associator may be arranged to associate other predetermined nodes with the outside to the track.
Conveniently, the node associator is arranged to associate nodes associated with the inside of the track with convex corners of the object to be machined. The node associator may be arranged to associate nodes associated with the outside of the track with concave corners of the object to be machined.
Conveniently, the processing circuitry further comprises a curve associator arranged to associate a curve with each of the nodes produced by the node associator. Preferably, the curve associated with the node by the curve associator has a radius corresponding to the minimum radius of a path of the material-remover of the machine tool. Such an arrangement ensures that it is possible to arrange the path for the material-remover such that it does not result in the velocity of
Cadugan Erica
Delcam PLC
Michael & Best & Friedrich LLP
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