Turning – Lathe – Attachment
Patent
1995-12-01
1998-02-24
Bishop, Steven C.
Turning
Lathe
Attachment
33630, 33638, 33572, 82173, 409133, B23B 2506, G01D 2100, G01B 500, B23Q 1722
Patent
active
057202095
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a mounting device for a telescopic transducer such as a ball-bar, used for measuring the ability of the movable arm of e.g. a machine tool, such as a milling machine or a lathe, to describe a predetermined trajectory, which is usually circular. Telescopic ball-bars are known as such from, U.S. Pat. No. 4,435,905, GB 2210978, EP 526056, and EP 0508686 and include a pair of spheres and a telescopic transducer. Typically, one of the spheres is universally pivotally mounted to a fixed point on the machine, while the other sphere is universally pivotally mounted to the movable arm thereof. Any variation in the distance between the spheres during circular motion of the movable arm about the fixed point (known as following error) will be measured by the telescopic transducer, and is indicative of the extent to which the trajectory of the movable arm varies from a circular trajectory. The data acquired from the telescopic transducer can be used to correct any such error, together with other machine errors such as backlash and squareness (for example).
A problem exists when attempting to use such a ball-bar to check the following error of a lathe, in that one end of the ball-bar is fixedly mounted to the tool post of the lathe, while the other end must be fixedly mounted with respect to the spindle. Hitherto, this has meant that, with the ball-bar connected, the tool post has only been able to execute approximately one quarter of a circular trajectory. This severely limits the amount of data acquired, and the value of such data for performing calibrations and error compensation.
OBJECTS OF THE INVENTION
The present invention seeks to overcome this problem by providing a mounting device for mounting a telescoping ball-bar between the spindle and the tool post of e.g. a lathe, which enables a trajectory of in excess of 180.degree. to be executed by the tool post.
A first aspect of the present invention provides a device for mounting an elongate telescopic transducer to a rotatable shaft of a machine tool, the device comprising: a carrying shank, retainable on a rotatable shaft of the machine; and a supporting member extending from the carrying shank which rigidly supports a fixture for receiving one end of the transducer, the fixture being spaced apart from the shank in a direction defining an axis of the device, wherein the supporting member has a cutaway portion which provides a free space between the fixture and the shank along a line defined by the axis, which, when the transducer is pivotally mounted to said fixture, enables the free end of the transducer to pivot along a path intersecting said axis.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example, and with reference to the accompanying drawings in which:
FIG. 1 is a schematic view of a lathe;
FIG. 2 is a side elevation of a mounting device in accordance with the present invention;
FIG. 2A is an alternative embodiment of a mounting device according to the present invention.
FIG. 3 is a view on III--III in FIG. 2; and
FIG. 4 illustrates the mounting device of the present invention in use on the lathe of FIG. 1; and
FIG. 5 is a section on V--V in FIG. 4.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to FIG. 1, a machine tool in the form of a lathe includes a rotatable shaft in the form of a spindle 10 (which rotates about an axis A) having a chuck 12 with three equi-spaced, axially extending and radially movable jaws 14 which grip a workpiece. Machining of such a workpiece is performed by moving a tool supported on a tool carrier provided by a tool post 16 relative to the spindle until the tool (not shown) comes into contact with the workpiece. The tool post 16 is movable relative to the spindle in three orthogonal directions x,y,z. Displacement of the tool post 16 relative to a datum whose position is fixed with respect to the spindle 10 is measured by three linear encoders, and movement of the tool post 16 relative to the d
REFERENCES:
patent: 4435905 (1984-03-01), Bryan
Bailey Andrew M.
Chapman Mark A. V.
Bishop Steven C.
Renishaw plc
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