Cutting machine for pits on CD master

A cutting machine for cutting pits on a laser disc master comprising a disc signal source with a RAM and a series of shift registers; a machine unit having a servo-rotary shaft for mounting a master disc; a servo-horizontally moving shaft perpendicular to the rotary shaft; a deviation sensor mounted on the horizontally moving shaft perpendicular to the master disc; and a diamond cutting tool controlled by a signal-source-controlled piezoelectric driver. It also comprises a computer unit, which includes a disc signal control interface, and machine unit control interfaces. The rotation error of the machine unit can modulate the signal output speed of the signal source.

BACKGROUND OF THE INVENTION 
The compact disc can be used for storing a high density of digital data; 
the data are to be stored by means of a plurality of pits having different 
lengths and spaces along a spiral track around the center of the disc. 
The compact disc usually includes a transparent substrate molded with a 
plurality of pits, a metallic coating on the substrate that can reflect 
the laser light, and a protective layer added as the surface. When reading 
out the data in a compact disc, a tiny laser in the player is focused on 
the spiral track from beneath while the compact disc is rotated at a 
constant linear velocity. The depth of the pits is equal to one half of 
the wave length of the laser (such as 0.1 mm). Since the pits and the 
plane portions (called lands) have a phase differential relation upon 
reflecting the laser beam, a different light contrast signal can be sensed 
corresponding to the length and space of the pits; that light contrast 
signal is then converted into an electronic signal, and decoded as on-off 
binary 1s and 0s (bits), which can be decoded, with a microprocessor, into 
the original data. The conventional laser recording method utilizes a 
photoresist layer deposited on a glass substrate. During the recording 
process, it is exposed by the laser beam which is modulated by the signal, 
then the pits are created during the development process of the 
photoresist layer, and then a silver film is coated thereon before the 
galvanic process needed for the manufacture of the pressing tools. The 
aforesaid manufacturing steps must be performed in a clean room 
environment, i.e., the manufacutring steps are cumbersome, and facilities 
therefore are expensive; as a result, the price of the laser disc is 
unable to be reduced. 
The method of making the conventional record (LP) by using a diamond tool 
for the master has been used for making a CED video disc successfully. 
However, the quality of the LP is less than the laser video disc; for 
instance, the recorded data are analog signals, which when replayed have 
an inferior quality compared to digitally recorded signals. As a result, 
CED video disks were not manufactured in large quantity for commercial 
purpose. 
In view of the aforesaid fact, an ideal and practical machine is necessary, 
which uses a diamond tool to cut pits directly on a master disc, so that 
the master disc make may be used directly, or used to duplicate compact 
discs in a mass production manner so as to lower the manufacturing cost, 
and to store the data thereon with digital signal to improve the quality 
of data. Since the recording pits on the compact disc are of high 
precision, the relationship between the cutting tool and the master disc 
and the moving speed thereof must be controlled accurately; therefore, a 
special control device is required to control the operation. In the 
conventional laser disc, the signal source for recording the master disc 
is from a PCM (pulse code modulation) tape machine, being played at a 
constant speed, which is unable to adapt to the characteristics of a 
machine using a tool to cut pits. Therefore, a special signal source means 
is required. 
According to the aforesaid idea, the present invention has been developed 
to provide: 
(1) a cutting machine which comprises a mechanical structure and a control 
device for executing an accurate operation between the cutting tool and 
the master disc; 
(2) a signal source for the cutting machine, of which the output signal 
speed can fit the characteristics of the cutting machine. 
SUMMARY OF THE INVENTION 
This invention provides a cutting machine for pits on a compact disc master 
(cutting machine), comprising a computer unit, a disc signal source, and a 
machine unit. The disc signal source includes a RAM having sufficient 
storage capacity, and a series of shift registers able to be modulated. 
The machine unit includes a serve-rotary shaft for mounting a master disc, 
horizontally-moving servo-shaft perpendicular to the rotary shaft, a 
deviation sensor mounted on the horizontally moving shaft and 
perpendicular to the master disc, and a diamond tool piezoelectrically 
driven by the disc signal source. The computer unit includes a 
microprocessor, a disc signal control interface, and control interfaces of 
the machine unit. The output speed of the signal source is to be modulated 
in accordance with the rotating error of the machine unit.

DETAILED DESCRIPTION 
The cutting machine according to the present invention comprises a computer 
unit, a disc signal source, and a machine unit. The disc signal source 
includes a large RAM and a series of adjustable shift registers. The 
machine unit includes a servo-rotary shaft for holding the master disc, a 
servo-controlled horizontally moving shaft, a deviation sensor mounted on 
the horizontally moving shaft and perpendicular to the master disc, and a 
diamond tool piezoelectrically driven by the signal from the signal source 
unit. The computer unit includes a microprocessor, a disc signal source 
control interface and control interfaces to the machine unit. The output 
speed of the signal source is to be regulated in accordence with the speed 
error of the machine unit. The structure and characteristics of this 
machine will further be described in detail with reference to the drawings 
in the follow paragraphs. 
FIG. 1 illustrates the structure of the present invention, which comprises 
three major components, i.e., a computer unit 1, a disc signal source 2, 
and a machine unit 3. The computer unit 1 includes a microprocessor 10 
electrically connected to the disc signal source 2 via a signal control 
interface 11, and servo-control interfaces 12 and 13 connecting 
microprocessor 10 electrically with the horizontally moving shaft 
servo-control circuit (position servo) 32 of the machine unit 3 and the 
rotary shaft servo-control circuit (spindle servo) 33 respectively, so as 
to control the motion of the horizontally moving shaft X and the rotary 
shaft W. The rotary shaft W has a working table 342 for holding the metal 
master disc 4; the rotary shaft W is driven by motor 340, and is 
servo-controlled by means of a feedback signal from a rpm sensor 341. The 
horizontally moving shaft X has a sliding block 352 perpendicular to the 
rotary shaft W, i.e., being parallel with the surface of the master disc 
4. The shaft X is actuated with the actuating device 350, and is 
servo-controlled by means of a displacement sensor 351, such as a laser 
measurement device. Under the sliding block 352 and perpendicular to the 
master disc 4, a piezoelectric crystal 310 is fixedly mounted via a damper 
311. A diamond-like cutting tool 36 is fixedly mounted under the 
piezoelectric crystal 310, perpendicular to the master disc. The cutting 
tool 36 has a suitable blade so as to cut into the master disc 4 or to be 
lifted above the disc upon the piezoelectric crystal 310 changing its 
dimension and upon the rotary shaft rotating. A distance deviation sensor 
37 has a distance-sensing head 370, which may be a capacitor-type sensor 
or a laser measurement device mounted on the sliding block 352 
perpendicular to the master disc 4 and closely beside the cutting tool 36 
so as to sense the position error along the axial direction Y during 
cutting operation; the error sensed will be converted into an electric 
signal to be coupled into a first differential amplifier 38 so as to 
modify and compensate the voltage level of the output signal 200 from the 
disc signal source 2, and then the piezoelectric crystal driver 31 will 
drive the piezoelectric crystal 310 and the cutting tool 36 to move up and 
down for controlling the pits cut in an accurate depth. Since the compact 
disc access is done at a linear constant velocity, the rpm of the rotary 
shaft W with the master disc is adjusted in accordance with the radius 
portion of the cutting tool 36, and also with the output speed of the 
signal 200 of the disk signal source 2; therefore, the speed control 
between the disc signal source 2 and the machine unit 3 has been 
particularly designed. 
In FIG. 2, the disc signal source 2 has a series of shift registers 20 to 
send out the disc signal data stored in a RAM 21. The RAM 21 has at least 
a sufficient capacity equal to a memory capacity of a disc (for example, 
600 million bytes for a 4.7 in. disc) so as to record the signal data of a 
PCM tape machine or a DAT (digital audio tape) unit. By using the series 
of shift register 20, the speed of the output signal 200 can suitably be 
adjusted so as to adapt to the characteristics of the cutting tool 36; 
especially, the output speed of the output signal 200 can be adjusted 
immediately in accordance with the actual rotating speed of the master 
disc 4 so as to obtain accurate length and space between the disc pits. 
The microcomputer unit 1 can calculate the correct rpm of the motor 340 on 
the rotary shaft W with the compact disc in accordance with the position 
of the cutting tool 36 on the radius of the compact disc 4 (as shown in 
FIG. 1, that is to be sensed with the displacement sensor 351); the 
rotating speed instruction is then transmitted into a second differential 
amplifier 22; that instruction signal is then combined with the error 
value generated by the error counter 24 resulting from the actual feedback 
rotating speed signal out of the rpm sensor 341; the combined signal then 
passes through a digital-to-analog transducer 23, and is coupled to a 
third differential amplifier 331 so as to be combined with the feedback 
signal of the rpm sensor 341, whereby a further precise vector circuit is 
formed; finally, the signal will control the motor 340 to rotate at an 
accurate speed through the rpm servo-controller 332 and the motor driver 
333. Moreover, the error value generated from the error counter 24 will be 
transmitted into a fourth differential amplifier 25 so as to combine with 
the standard clock pulse generated by the computer unit 1; then, the 
signal will pass through the voltage-to-frequency transducer 26 to 
generate a compensating pulse for controlling the series of shift 
registers 20 so as to adapt to the minor rpm error of motor 340 and to 
send out an accurate disc signal 200; then, an accurate pit-cutting 
operation on the disc 4 can be conducted by using together with the 
aforementioned first differential amplifier 38, the piezoelectric crystal 
driver 31, the piezoelectric crystal 310, the cutting tool 36, and the 
distance deviation sensor 37.