GB1583832A - Tool holders - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO TOOL HOLDERS (71) We, FEDERAL-MOGUL WEST WIND AIR BEARINGS LIMITED, a British Company of, Dalling Road, Branksome, Poole, Dorset BH12 1LG., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow instatement:- This invention relates to tool holders comprising a radially deformable (e.g., contracting) collet or chuck for holding a tool.

In many processes that involve changing tools, for example in circuit board drilling machines, the manual changing of tools using nutted collets is impracticable. The main object of the present invention is to provide a tool holder that enables the opening and closing of a collet or chuck to be effected by remote means, while being driven electncally by means integral with the tool holder.

According to the invention, a tool holder comprises a hollow rotary shaft, a collet or chuck mounted coaxially at one end of the shaft and arranged to be opened and closed, by axial movement with respect to the shaft, between a tool gripping position and a tool releasing position, spring means mounted in the shaft for biasing the collet or chuck in an axial direction, and an actuating member extending through the shaft to remotely controlled means in the holder for driving the actuating member axially to move the collet or chuck from one said position to the other said position, the actuating member thereby determining, in conjunction with the spring means, the open or closed condition of the collet or chuck, the tool holder further containing a squirrel cage motor having a wound stator surrounding a central portion of the shaft and a rotor consisting of copper bars and rings inset in the shaft and the shaft when in operation being supported by air journal bearings.

Advantageously, the spring means are so stressed within the shaft as to maintain the collet or chuck in position for gripping a tool and the remotely controlled means are arranged to apply axial pressure on the actuating member to force the collet or chuck, while further stressing the spring means, to a position in which it will release a tool.

The spring means may advantageously be a bank of disk springs maintained under compression to hold a conical surface on a collet in engagement with a mating surface in the shaft. The actuating member may then be a thrust rod arranged to apply axial pressure to the disks, thereby releasing the collet from the shaft. The remotely controlled means may very conveniently be fluid (e.g. air) operated means comprising a piston at the end of the thrust rod. The piston may be a sliding fit in a cylinder or sealed by a diaphragm to the wall of a chamber in which the piston is located out of contact with the chamber wall. In this arrangement, admission of fluid pressure to a space beyond the piston may be arranged to cause the collet to open and release of such pressure to enable the spring disks to close the collet.

In order that the invention may be clearly understood and readily carried into effect one example thereof will now be described, by way of example, with reference to the accompanying drawing which is a longitudinal transverse section through a power driven tool holder.

The tool holder comprises a body 20 containing a hollow rotary shaft 2 dnven by a squirrel cage motor (not shown) built into the body 2 as described in Patent Specification No. 1,427,818. That is to say, a wound stator surrounds a central portion of the shaft 2 which has inset copper bars and rings. Air journal bearings (not shown) for the shaft 2 are provided ahead of and to the rear of the motor. A flange 21 on the shaft 2 forms part of a thrust air bearing, the air ducts for which are not shown. The forward end of the shaft 2 is formed with a conical bearing surface which engages a conical surface 22 on a split collet 1 that is also formed with a cylindrical surface 23 that slides in a cylindrical portion of the shaft 2. A bulkhead 4 is fixed in the shaft 2 and a headed pin 3, fixed axially to the collet 2, extends through this. A bank of disk springs 24 is interposed between the bulkhead 4 and the head of the pin 3. The springs 24 are under considerable compression so as to draw the collet firmly into the shaft 2, causing the conical bearing surface to make the collet 1 firmly grip a tool 5.

Clearly, in order to enable the tool 5 to be removed or replaced, the pin 3 must be moved axially to relieve the radial pressure on the collet. For this purpose, an actuating member in the form of a thrust rod extending axially into and through a considerable length of the shaft 2, is mounted in a tightly fitting bearing 8 in the body 20. A piston 9 is fixed to the end of the rod 7 remote from the collet and is located in a chamber 10 in the body 20, the chamber 10 being closed by a plate 25 formed with a fluid inlet port 13. The face of the piston 9 is sealed to the body 20 by a "Bellofram" rolling diaphragm 26. A spring 11 between the body 2 and the piston 9 prevents the rod 7 from contacting the head of the pin 3 until fluid pressure is admitted to a zone 12 between the diaphragm 26 and plate 25.

When fluid pressure is admitted to the zone 12, the rod 7 presses on the pin 3, increasing the compression in the springs 24 and moving the collet axially to relieve it from the radial pressure on the surface 22.

The tool holder is particularly applicable to the case where the spindle 2 is mounted in an air bearing, although other forms of bearing can, of course, be used.

In a modification of the tool holder shown in the drawing means are provided for preventing fine dust particles from finding their way between the collet 1 and shaft 2. This is a risk when drilling circuit boards for example. In this modification the rod 7 takes the form of a thick walled narrow bore tube along which air can pass, when admitted to the zone 12. The head of the pin 3 is notched, an axial hole is drilled in the bulkhead 4 and axial notches are formed in the cylindrical surface 23 of the collet 1. Therefore, the air escaping from the tubular rod escapes to atmosphere by way of the slots in the conical part of the collet 1 and automatically keeps dust clear of the collet during tool changing.

WHAT WE CLAIM IS: 1. A tool holder comprising a hollow rotary shaft, a collet or chuck mounted coaxially at one end of the shaft and arranged to be opened and closed, by axial movement with respect to the shaft, between a tool gripping position and a tool releasing position, spring means mounted in the shaft for biasing the collet or chuck in an axial direction, and an actuating member extending through the shaft to remotely controlled means in the holder for driving the actuating member axially to move the collet or chuck from one said position to the other said position, the actuating member thereby determining, in conjunction with the spring means, the open or closed condition of the collet or chuck, the tool holder further containing a squirrel cage motor having a wound stator surrounding a central portion of the shaft and a rotor consisting of copper bars and rings inset in the shaft and the shaft when in operation being supported by air journal bearings.

2. A tool holder according to Claim 1, in which the spring means are so stressed within the shaft as to maintain the collet or chuck in position for gripping a tool and the remotely controlled means are arranged to apply axial pressure on the actuating member to force the collet or chuck, while further stressing the spring means, to a position in which it will release a tool.

3. A tool holder according to Claim 2, in which the spring means is a bank of disk springs maintained under pressure to hold a conical surface on a collet in engagement with a mating surface in.the shaft, the actuating member being a thrust rod arranged to apply increased axial pressure to the disks, thereby releasing the collet from the shaft.

4. A tool holder according to any one of the preceding claims, in which the remotely controlled means comprise a piston at the end of the actuating member remote from the collet or chuck and reciprocable in a chamber in the holder under control of fluid pressure selectively admitted to the chamber.

5. A tool holder according to Claim 4, in which the piston is mounted so as to be out of contact with the chamber wall and is sealed to the chamber wall by a flexible diaphragm.

6. A tool holder with substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. through this. A bank of disk springs 24 is interposed between the bulkhead 4 and the head of the pin 3. The springs 24 are under considerable compression so as to draw the collet firmly into the shaft 2, causing the conical bearing surface to make the collet 1 firmly grip a tool 5. Clearly, in order to enable the tool 5 to be removed or replaced, the pin 3 must be moved axially to relieve the radial pressure on the collet. For this purpose, an actuating member in the form of a thrust rod extending axially into and through a considerable length of the shaft 2, is mounted in a tightly fitting bearing 8 in the body 20. A piston 9 is fixed to the end of the rod 7 remote from the collet and is located in a chamber 10 in the body 20, the chamber 10 being closed by a plate 25 formed with a fluid inlet port 13. The face of the piston 9 is sealed to the body 20 by a "Bellofram" rolling diaphragm 26. A spring 11 between the body 2 and the piston 9 prevents the rod 7 from contacting the head of the pin 3 until fluid pressure is admitted to a zone 12 between the diaphragm 26 and plate 25. When fluid pressure is admitted to the zone 12, the rod 7 presses on the pin 3, increasing the compression in the springs 24 and moving the collet axially to relieve it from the radial pressure on the surface 22. The tool holder is particularly applicable to the case where the spindle 2 is mounted in an air bearing, although other forms of bearing can, of course, be used. In a modification of the tool holder shown in the drawing means are provided for preventing fine dust particles from finding their way between the collet 1 and shaft 2. This is a risk when drilling circuit boards for example. In this modification the rod 7 takes the form of a thick walled narrow bore tube along which air can pass, when admitted to the zone 12. The head of the pin 3 is notched, an axial hole is drilled in the bulkhead 4 and axial notches are formed in the cylindrical surface 23 of the collet 1. Therefore, the air escaping from the tubular rod escapes to atmosphere by way of the slots in the conical part of the collet 1 and automatically keeps dust clear of the collet during tool changing. WHAT WE CLAIM IS:

1. A tool holder comprising a hollow rotary shaft, a collet or chuck mounted coaxially at one end of the shaft and arranged to be opened and closed, by axial movement with respect to the shaft, between a tool gripping position and a tool releasing position, spring means mounted in the shaft for biasing the collet or chuck in an axial direction, and an actuating member extending through the shaft to remotely controlled means in the holder for driving the actuating member axially to move the collet or chuck from one said position to the other said position, the actuating member thereby determining, in conjunction with the spring means, the open or closed condition of the collet or chuck, the tool holder further containing a squirrel cage motor having a wound stator surrounding a central portion of the shaft and a rotor consisting of copper bars and rings inset in the shaft and the shaft when in operation being supported by air journal bearings.

2. A tool holder according to Claim 1, in which the spring means are so stressed within the shaft as to maintain the collet or chuck in position for gripping a tool and the remotely controlled means are arranged to apply axial pressure on the actuating member to force the collet or chuck, while further stressing the spring means, to a position in which it will release a tool.

3. A tool holder according to Claim 2, in which the spring means is a bank of disk springs maintained under pressure to hold a conical surface on a collet in engagement with a mating surface in.the shaft, the actuating member being a thrust rod arranged to apply increased axial pressure to the disks, thereby releasing the collet from the shaft.

4. A tool holder according to any one of the preceding claims, in which the remotely controlled means comprise a piston at the end of the actuating member remote from the collet or chuck and reciprocable in a chamber in the holder under control of fluid pressure selectively admitted to the chamber.

5. A tool holder according to Claim 4, in which the piston is mounted so as to be out of contact with the chamber wall and is sealed to the chamber wall by a flexible diaphragm.

6. A tool holder with substantially as hereinbefore described with reference to the accompanying drawing.