Shaft for a motor-driven spindle

A shaft for a motor-driven spindle including an elongate section made of a reinforced plastic material and a rotor arranged around the elongate section and surrounded by reinforced plastic material. The rotor may be wound by the reinforced plastic material and if it includes grooves on an outer circumference, the reinforced plastic material is wound into the grooves. A faceted wheel may be provided on the shaft and include reflective surfaces on an outer circumference thereof. The shaft is arranged in a housing of the motor-driven spindle.

FIELD OF THE INVENTION 
The present invention relates to a shaft for a motor-driven spindle and a 
motor-driven spindle including the same. 
BACKGROUND OF THE INVENTION 
Motor-driven spindles find many applications in industry and technology. 
They basically consists of a shaft mounted in a housing. The shaft is 
driven in many cases by electrical motors. The shaft is supported in the 
sleeve generally by means of roller bearings or air bearings. 
Known spindles have one particular disadvantage in that there are speed 
limitations due to the centrifugal forces arising during operation, in 
particular at higher rotational speeds. These centrifugal forces affect 
the running precision of the shaft and may adversely affect the attachment 
of a rotor mounted on the shaft. As a result, the generation of the 
centrifugal forces determines capacity limits for conventional spindles. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide new and improved shafts 
for motor-driven spindles. 
It is another object of the present invention to provide shafts for 
motor-driven spindles in which the disadvantages of the conventional prior 
art motor-driven spindles are substantially avoided. 
It is yet another object of the present invention to provide motor-driven 
spindles which are capable of rotating at high rotational speeds. 
In order to achieve these objects and others, a shaft for a motor-driven 
spindle in accordance with the invention includes an elongate section made 
of a reinforced plastic material and a rotor arranged around a part of the 
elongate section and incorporated into the reinforced plastic material. 
The rotor may be wound with the reinforced plastic material and if it 
includes grooves on an outer circumference, the reinforced plastic 
material may be wound into the grooves. The reinforced plastic material 
may be a carbon fiber laminate. 
A motor-driven spindle in accordance with the invention includes a housing, 
a shaft arranged in the housing and made of reinforced plastic material, 
the shaft having an elongate section, and power means for rotating the 
shaft. The power means comprise a stator and a rotor which is arranged 
around a part of the elongate section of the shaft and incorporated into 
the material of the shaft. The shaft may include a faceted wheel having a 
plurality of reflective surfaces on an outer circumference thereof. The 
housing therefore includes an optical window for allowing penetration of 
laser rays into contact with the reflective surfaces on the faceted wheel. 
In a method for making a shaft for a motor-driven spindle in accordance 
with the invention, carbon fibers are wound into the form of a shaft, the 
carbon fibers are embedded in plastic material, a circular rotor is 
arranged around a part of the shaft, and reinforced plastic material is 
wound around the rotor to incorporate the rotor into connection with the 
shaft, i.e., embed the rotor within the material of the shaft to thereby 
form a unitary structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the accompanying drawing, a preferred embodiment of a 
motor-driven spindle including a shaft according to the invention is 
shown. The motor-driven spindle includes a housing 2 and a shaft 1 
arranged in the housing 2. Shaft 1 has an elongate, tubular section and a 
faceted wheel 11 with twenty-five (25) reflective, mirror surfaces on the 
circumference arranged at a location along the length of the elongate 
portion. Shaft 1 is made of composite material or carbon fiber laminate. 
The housing 2 also defines at least one optical window 3 in an outer 
surface thereof for allowing the entry and exit of laser rays and is 
positioned to allow the laser rays to reflect against the surfaces on the 
faceted wheel 11. A guide bushing 4 is arranged in the housing 2. Power 
means for driving the shaft 1 are provided in the housing 2 and comprise a 
stator 5 and a rotor or permanent magnet 6. An axle 7 extends through the 
shaft 1. A closing lid 8 is arranged at a side of the housing 1 alongside 
the stator 5 and rotor 6. A bearing gap or radial air gap 9 (aerodynamic 
radial bearing) is defined between the shaft 1 and the axle 7 by 
appropriate dimensioning and placement of the shaft 1 and axle 7. A 
bearing gap or axial bearing 10 (aerodynamic axial bearing) is defined 
between the faceted wheel 11, adjacent surfaces of the guide bushing 4 and 
adjacent surfaces of the housing 2 by appropriate dimensioning and 
placement of the shaft 1, the guide bushing 4 and the housing 2. 
The shaft 1 rotates on the radial air gap 9 around the axle 7. The lateral 
surfaces of the faceted wheel 11 are used to define the axial bearing 10. 
The faceted wheel 11 comprises 25 surfaces on the circumference (similar 
to key surfaces). These surfaces are made into mirrors and serve to 
deflect a laser ray contacting the surfaces through optical window 3. Each 
facete is used to illuminate an image cell. 
Stator 5 and rotor 6 together make up a direct-current motor which is 
commutated via hall-effect IC's. 
In accordance with the invention, the shaft 1 and the rotor 6 constitute a 
solid unit. The shaft 1 is made of carbon fiber laminate material, whereby 
the carbon fibers are wound into the form of the shaft and are imbedded in 
plastic. Thus, reinforced plastic materials are known. The rotor 6 is 
placed around a part of the shaft 1 and then is surrounded by the basic 
shaft material (carbon fiber laminate) to thereby form a projecting 
portion of the shaft 1, i.e., it projects beyond the cylindrical envelope 
defined by the elongate section of the shaft 1. More particularly, the 
fibers of the basic material are wound around the soft magnet (rotor 6) 
under tension. The arming by this fiber bandage makes it possible to 
obtain circumferential speeds of about 150 m/sec on the outside diameter 
of the magnets, with a ring width greater than about 2 mm. 
This bandage makes it possible to use larger magnets and thereby motors 
with greater capacities than is possible with steel arming. 
The faceted wheel 11 is wound in surrounding fibers and is alternately 
soaked with bonding material (e.g., synthetic resin) until the final 
diameter is reached. 
According to the invention the following task is accomplished: 
The shaft 1 has a speed of about 150,000 l/min, supported by a dynamic air 
bearing. The shaft should have a maximum of precision at about 150,000 
l/min. The repeatable axle wobble is less than three (3) angular seconds, 
the non-repeatable less than one (1) angular second. 
The following advantages are obtained over a conventional steel design: 
Owing to the low weight and the great solidity of carbon fiber laminate 
materials, the shaft is able to attain twice the speed for the same 
dimensions (i.e., the same static base load). 
The influence of the centrifugal force is low, and therefore the air gap is 
constant and the required rigidity is ensured (and with it again the 
running precision). 
Owing to the low weight and the high degree of solidity of the carbon fiber 
laminate materials, the flexibility in configuration and its 
characteristic of being non-magnetizable, the rotor 5 which is soft by 
comparison for highest speeds (the rotor of the DC motor or asynchronous 
motor) can be easily used. Thus, this rotor cannot be deformed through 
centrifugal force. 
The running precision is maintained. 
In view of the fact that carbon fiber laminate materials cannot be 
magnetized, the rotor armature made of this material has no eddy current 
losses. 
Due to its composition, it is possible to use the carbon fiber laminate 
material with excellent results together with steel and ceramic in dynamic 
air bearings. 
The gliding characteristics of this material are outstanding. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the teachings hereof Therefore, it is to be 
understood that the invention can be varied from the detailed description 
above within the scope of the claims appended hereto.