Chuck with linear motor for axially moving a tool

Abstract: A tool-holding chuck (1) for machining with the removal of swarf in which rotary movement of the chuck (1) and a tool (2) coaxially fixed to it and axial forward and backward movement of the tool (2) are required, in which the tool (2) is fixed in a hollow member (7) which can move axially and rotate with respect to the body (1d) of the chuck (1) within which it is housed, magnets (4n) forming part of a linear motor (4) whose stator windings (4s) are housed in the body (1d) of the said chuck (1) around the hollow member (7) being fixed to the said hollow member (7), is described.

Description: This invention relates to the field of machine tools which carry out machining by the removal of swarf, and more particularly those of them which require rotary working motion of the tool as well as further linear axial forward and backward motion (to carry out the working travel and then return to the initial position). According to the present state of the art the said axial motion is normally provided by either a linear motor (see e.g. US-A-4 761 876, which document discloses the features of the preamble of claim 1.) or mechanical movement systems of similar effect which act on the slide which supports the tool-bearing chuck as a whole. (Both these systems are well-known to those skilled in the art). The main disadvantages resulting from such systems are the relative slowness with which they operate, structural complexity and relatively large dimensions for the tool-holding stations, factors which obviously have adverse repercussions on costs. The inventor of this invention has conceived a solution which avoids all the abovementioned disadvantages and which essentially comprises causing forward and backward movements of the tool to be performed by a linear motor comprising a stator with electromagnetic induction windings housed in the body of the chuck and a moving part provided by permanent magnets (the fields from which interact with those created by the said windings) integrally attached to the tool. If the current passing through the said stator windings is suitably directed and if the said permanent magnets are orientated suitably and in an appropriate way, it is then readily possible to move the tool axially with appreciable speed as a result of the low mass of the moving parts, including the tool. Tests performed by the inventor on prototype chucks according to the invention have in fact shown the possibility that a tool can be moved axially in both directions, imparting to it an acceleration which is up to six times the acceleration of gravity g. This means that a tool can be moved by imparting an acceleration of approximately 59 m/s 2 to it; this fact provides a clear idea of the speed of operation of a chuck according to the invention. In accordance with what has been said so far, the subject matter of this invention comprises a tool-holding chuck according to Claim 1. A more detailed description of a preferred embodiment of a tool-holding chuck according to the invention will now be provided, and in so doing reference will also be made to the appended drawings, which show: In Figure 1, a longitudinal cross section of the said embodiment of a chuck according to the invention, In Figure 2, a longitudinal cross section of only one hollow member forming part of the chuck within which a tool is secured, In Figure 3, a transverse cross section of the hollow member in Figure 2 in the area in which the moving permanent magnets of the linear motor are applied. Considering first Figure 1: this shows how within body 1d of a chuck 1 there is a hollow member 7 connected in such a way that it can rotate and move axially with respect to it. A small shaft 3 (which is also hollow in the case in question), which has a cavity 3c within which a tool 2 is fixed, is fixed coaxially and integrally with said hollow member 7. On the outer surface Se of said shaft 3 there are fixed a plurality of permanent magnets 4n which are housed in a suitable recess 7i provided in said hollow member 7. These magnets 4n are the moving part of a linear motor 4 whose stator windings 4s are located around hollow member 7 and anchored in body 1d of the chuck. In the case in point these windings are simply wound circumferentially around hollow member 7 and said permanent magnets 4n, and magnets 4n themselves have their N, S polarities orientated in such a way that they are subject to an axial thrust in two directions as a result of the magnetic fields generated by the passage of current running in opposite directions through the said stator windings (4s). By suitably directing the said currents it is therefore possible to move hollow member 7, and consequently tool 2, axially, causing the latter to perform its forward working movement and its disengaging and return movement to initial stand-by conditions. One end of said hollow member 7, free end 7e located at the opposite end from tool 2, has fixed to it rotor 6r of an electric motor 6 whose stator 6s has its windings housed and anchored in the body 1d of chuck 1. By starting aforesaid electric motor 6, hollow member 7 and tool 2 which is integral with it are caused to rotate at the desired working speed (up to 300,000 rpm in the case of systems of small mass and little resistance to forward movement). Thus the conditions for moving tool 2 simultaneously with rotary movement about its own axis x-x (by means of electric motor 6) and axial movement in alternating directions along that axis (by means of linear motor 4) are created. Given the small size of the mass of the entire moving part of the equipment, that is the system comprising hollow member 7, magnets 4n, the small shaft and tool 2, high values of the various speeds already mentioned can be achieved without it being necessary to move systems of appreciable mass which incorporate appreciable inertia, as in the state of the art. The result which the inventor set himself, that is of having a tool-holding chuck of high performance with a high productive capacity is therefore achieved. In the particular embodiment illustrated heretofore the inventor provides for the use of two sets of 4 magnets 4n of boron-iron-neodymium with S-N polar axes parallel to the x-x axis and spaced apart by radially orientated gap spaces 5t which can be filled with one of those synthetic resins well known to those skilled in the art of magnetic and electromagnetic equipment; other types of magnets, which may be arranged in different ways, may also be used. Again in the case in question, electric motor 6 which causes hollow member 7 and tool 2 to rotate is of the asynchronous type, with a squirrel cage winding, but other types of motor may also be used without adverse consequences. Similarly, all the component parts such as hollow member 7, small shaft 3 and the various parts comprising linear motor 4 may be different in nature, shape, position and attachment with respect to the aim of providing a chuck according to the invention which differs from that described, but still derives from the teaching included in appended Claim 1. It is obvious that these embodiments will also lie within the scope of the protection conferred by this patent application.

Claims: Tool-holding chuck (1) for machining with the removal of swarf in which rotary movement of the chuck (1) and a tool (2) coaxially fixed to it and axial forward and backward movement of the tool (2) are required, the tool (2) being fixed in a hollow member (7) which can move axially and rotate with respect to the body (1d) of the chuck (1) within which it is housed, characterized in that magnets (4n) are fixed to the said hollow member (7), said magnets (4n) forming part of a linear motor (4) whose stator windings (4s) are housed in the body (1d) of the said chuck (1) around the hollow member (7). Chuck according to Claim 1, in which the tool (2) is fixed in a cavity (3c) in a small shaft (3) housed coaxially within the said hollow member (7) with which it is incorporated. Chuck according to one of the foregoing claims, in which the said permanent magnets (4n) are orientated in such a way that they are thrust axially by the effect of the electromagnetic fields generated by the passage of currents which run in opposite directions within the said stator windings (4s), which are wound circumferentially around the said hollow member (7). Chuck according to either of Claims 2 or 3, in which the said permanent magnets (4n) have a transverse cross section in the shape of a sector of a circular crown, with the shorter curved side adhering to the cylindrical outer surface (Se) of the said small shaft (3). Chuck according to Claim 4, in which the said magnets (4n) are of boron-iron-neodymium, are two groups of four magnets each and are laterally separated from each other by a radially orientated air gap (5t). Chuck according to one of Claims 4 or 5, in which the said magnets (4n) are arranged in such a way that their axes linking the (N, S) polarities are orientated parallel to the axis (x-x) of the said hollow member (3) coaxially housing the tool (2). Chuck according to any one of the foregoing claims, in which one end (7e) of the said hollow member (7) is attached to the rotor (6r) of an electric motor (6) whose stator (6s) is fixed to the body (1d) of the chuck (1). Chuck according to Claim 7, in which the said electric motor (6) is of the type with a three phase stator (6s) and rotor (6r) with a squirrel cage winding. Chuck according to any one of the foregoing claims, characterized in that its body (1d) is attached to the machine tool which uses it by means (8) which permit it to move in a perpendicular direction with respect to the axis (x-x) of the tool (2).

Inventors: AMMANN BEAT, AMMANN, BEAT
Applicants: BALLADO INVEST INC, BALLADO INVESTMENTS INC.
Application year: 1999
Main classification: B23B31
IPC codes: B23Q5, H02K16, H02K17, H02K41, B23B31