WO2008086071A2

WO2008086071A2 - Hybrid acceleration system for spindle unit in a machine tool assembly

Info

Publication number: WO2008086071A2
Application number: PCT/US2008/050071
Authority: WO
Inventors: Steven S. Miyano; Thomas T. Miyano
Original assignee: Miyano Steven S; Miyano Thomas T
Priority date: 2007-01-03
Filing date: 2008-01-03
Publication date: 2008-07-17
Also published as: WO2008086071A3

Abstract

A computer controlled machine tool assembly has a spindle (150) attached to a main spindle shaft (144). A vector motor (168) is coupled to the main spindle shaft to control rotation of the main spindle shaft under computer control (182). A flywheel shaft (200) has a flywheel (206) and a speed sensor (210) for sensing a rotational speed of the flywheel shaft and is coupled to the main spindle shaft by a first pulley (218) through a computer controlled clutch (202). The computer controlled clutch engages the flywheel shaft to the main spindle shaft under computer control. An acceleration motor (164) is coupled to the flywheel shaft through a second pulley (208) and a one way clutch (204), where the acceleration motor is activated under computer control responsive to the rotational speed of the flywheel shaft.

Description

HYBRID ACCELERATION SYSTEM FOR SPINDLE UNIT IN A MACHINE TOOL ASSEMBLY

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 60/878,250, filed January 3, 2007.

FIELD OF THE INVENTION

[0002] This invention pertains to machine tools of the type having a rotatable spindle that carries a work piece for cutting and, more particularly, to a machine tool assembly that can be used to rapidly bring the machine tool spindle up to a predetermined operating speed.

BACKGROUND OF THE INVENTION

[0003] Machine tools are commonly designed with a rotary spindle with a chuck thereon to releasably hold a work piece for cutting. The spindle is driven by a vector motor, typically through one or more endless power transmission belts.

[0004] The chuck holds the work piece to be worked. The vector motor is used to accelerate the spindle to a predetermined operating speed, which requires time. For example, a computer numerically controlled (CNC) lathe will typically require about 4 -5 seconds to bring the chuck and spindle up to an operating speed of 4000 revolutions per minute (rpm). If a tooling/cutting operation is performed for 10 seconds, then the total cycle time from startup to completion is 15 seconds. If this operation takes 20 process cycles to complete, then the total operation time will be 300 seconds to machine the work piece, in this example.

[0005] It is known to increase the power output of the vector motor to effect a reduction in the startup time. To accomplish this, the vector motor, as well as an amplifier, must be scaled up. The result is generally a more expensive overall system, assuming the other components remain the same. [0006] Additionally, the higher output motor is more expensive to operate and is particularly inefficient when used in light machining operations.

[0007] Examples of conventional devices are further described in U.S. Patent No. 5,673,467 by Miyano et al. entitled MACHINE TOOL ASSEMBLY issued October 7, 1997, herein incorporated by reference in its entirety for all purposes.

[0008] In Figure 1, a prior art machine tool assembly is shown at 10. The machine tool assembly 10 is part of a machine tool system that is used to perform any of a number of different machining operations on a workpiece. The machining operations are performed utilizing a chuck 12 that is carried on a spindle 14, with the chuck 12 and spindle 14 being rotatable about an axis 16. The chuck 12, which may be part of a lathe, a milling machine, or the like, rotates any of a number of different cutting tools 18, 20, 22, 24. The cutting tools 18, 20, 22, 24 are in this particular assembly shown to be carried on a slide 26. The tools can be either manually or automatically placed into operative position in the chuck 12 and removed from the operative position in the chuck 12.

[0009] The spindle 14 and chuck 12 are driven in rotation about the axis 16 by a variable speed vector motor 28. The motor 28 has a rotatable shaft 30 with a pulley 32 at its distal end. The pulley 32 is aligned axially of the spindle with another pulley 34 carried by, and rotatable with, the spindle 14. Two endless power transmission elements 36 are trained around the pulleys 32, 34 and transmit power from the motor 28 to the spindle 14.

[0010] Since the spindle 14 and chuck 12 are driven solely by the motor 28 in the machine 10 of Figure 1, the motor 28 must have the capacity to drive the chuck 12 at the desired operating speed and with sufficient power to carry out the heaviest anticipated machining operations. Regardless of the power output capacity for the motor 28, there is a significant time lag that occurs in bringing the motor 28 up to speed from a stopped state. There is a further time lag in transmitting power between the pulleys 32, 34, by reason of the non-rigid interconnection there between. Accordingly, with the motor 28 stopped and the spindle 14 and chuck 12 at rest, a significant startup time is inherent in the assembly 10, regardless of the power output of the motor 28. [0011] An improved machine tool 40 is shown in Figure 2. The machine tool assembly 40 is part of an overall system at 42, which may be a single station or multi-station machine tool system.

[0012] The machine tool assembly 40 has a rotatable spindle 44 for driving a tool (in this example a drill bit 46), which is releasably carried in a chuck 48 at the end of the spindle 44. The machine tool assembly could be part of a lathe, or other type of machine tool using a rotatable spindle. The spindle 44 is driven to cause the tool 46 to perform a desired operation on a workpiece 50 supported at a work station 52.

[0013] The tool 46 can be used to perform multiple operations on each individual workpiece 50. Alternatively, workpieces 50 can be serially shuttled into working/operating position, as shown for the workpiece 50, at the work station 52.

[0014] Additional machining operations can be performed by tools 54, 56, carried on a gang tool slide 58. The individual tools 54, 56 can be manually placed in, and removed from, the chuck 48. Alternatively, systems well known to those skilled in the art are in existence that automatically effect interchange of the tools.

[0015] Means 60 is provided for driving the spindle 44 in rotation about its axis 62. The means 60 includes a first power source/motor 64 with first means at 66 cooperating between the motor 64 and spindle 44 for transmitting power from the motor 64 as a rotary drive force to the spindle 44.

[0016] The means 60 includes a second power source/motor with means at 70 cooperating between the motor 68 and spindle 44 for causing the motor 68 to drive the spindle 44 in rotation about its axis 62.

[0017] In this example, the motor 64 is a 20-30 h.p. general purpose inverter motor. The motor 64 has a two-part shaft 72 with first and second axially spaced parts 74, 76, respectively, operatively connected through a clutch mechanism at 78. The clutch mechanism 78, which is also part of the means 66, has engaged and disengaged states. In the disengaged state, the motor 64 can be operated without transmitting a rotative force to the spindle 44. In the engaged state, power from the motor is positively transmitted through the shaft parts 74, 76 and through a belt and pulley arrangement at 80 to the spindle 44.

[0018] The clutch mechanism 78 is changed between engaged and disengaged positions by a control means 82. The clutch mechanism 78 may be an automotive-type clutch. In one example, the clutch used on the Toyota Corolla model automobile would adequately perform the function described herein.

[0019] The shaft part 76 carries two axially spaced flywheels 84, 86 and a pulley 88 there between. The pulley 88 is axially aligned with a pulley 90 on the spindle 44. A plurality of axially spaced belts 92 are trained around the pulleys 88, 90 and transfer power from the pulley 88, driven by the motor 64, to the pulley 90, and in turn the spindle 44 on which it is mounted.

[0020] The motor 68, which, in this example, is a 10 h.p. vector motor, has a rotary shaft 94 that carries a pulley 96. The pulley 90 has a sufficient axial extent to align with the pulley 96 to allow, in this case, three axially spaced, endless power transmission belts 98 to be trained around the pulleys 90, 96, to allow power transmission from the pulley 96 to the pulley 90, and in turn to the spindle 44 which carries the pulley 90.

[0021] The control means 82 is operatively connected to the motors 64, 68, the clutch 78, and to a means at 100 for sensing the position of a workpiece 50 at the work station 52.

[0022] A typical operation of the machine tool assembly 40 will now be described. Initially, the machine tool assembly 40 is in a state wherein the clutch 78 is disengaged. The control means 82 causes the motor 64 to be powered until it reaches its normal operating speed.

[0023] With a tool 46 in the chuck 48 and a workpiece 50 in an operating position at the work station 52, a sensing means 100 produces a "completion of part loading" signal to the control means 82, which gives a "spindle start" command that causes the motor 68 to be started and at the same time causes the clutch 78 to be placed in its engaged state. Whereas use of the motor 68 alone would cause a significant time to pass between initial startup and the realization of the operating speed for the spindle 44, the pre-started motor 64, with the clutch 78 engaged, rapidly causes the spindle 44 to be brought up to a programmed operating speed.

[0024] The sensing means 100 may produce another signal indicative of a workpiece moving into and out of an operating position at the work station 52. This signal causes the clutch mechanism 78 to remain disengaged, the motor 64 to be brought up to a programmed speed, and the motor 68 to be stopped.

[0025] To further minimize this response time, flywheels 84, 86 are provided on the shaft part 76 to produce additional momentum that is transferred to the pulley 90 and associated spindle 44.

[0026] With this arrangement, spindle 44 can be rapidly brought up to speed. At the same time, the system benefits from the combined power of the motors 64, 68. By placing the clutch 78 in a disengaged state, the smaller motor 68 can be operated alone with the pulley 88 idling. This results in an energy savings.

[0027] The resulting system has flexibility from a power standpoint and also can, in most cases, be constructed more cheaply than the same system with a single 40 h.p. vector motor.

BRIEF SUMMARY OF THE INVENTION

[0028] In one exemplary embodiment, a flywheel 206 is mounted on a flywheel shaft 200. The flywheel shaft 200 is coupled to an acceleration motor 164 through a first pulley 208 and one way clutch 204. The flywheel shaft 200 is coupled to a main spindle shaft 144 of a machine tool 230 through a second pulley 218 that is engaged by a one way computer controlled clutch 202. The acceleration motor 164 and computer controlled clutch 202 are controlled by a control device 182. A flywheel speed sensor 210 provides the control device 182 with a speed signal indicating the rotational speed of the flywheel shaft 200. When the flywheel shaft 200 rotational speed drops below a predetermined level, the control device 182 activates the acceleration motor 164 to accelerate the flywheel shaft 200 to the predetermined level, at which point, the control device 182 deactivates the acceleration motor 164. When a computer controlled process calls for acceleration of the main spindle shaft 144, the control engages the one way computer controlled clutch 202 to transfer energy from the flywheel shaft 200 to the main spindle shaft 144.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Certain exemplary embodiments of the present invention will now be described with respect to the following drawings, wherein:

[0030] Figure 1 is a schematic view of a prior art machine tool assembly 10;

[0031] Figure 2 is a plan view of another conventional machine tool assembly 40;

[0032] Figure 3 is a plan view of one embodiment of a machine tool assembly 230 according to the present invention;

[0033] Figure 4 is a graph illustrating an example of the rotational speed of the flywheel shaft 200 as driven by the induction motor 164 in the operation of the tool 230 of Figure 3; and

[0034] Figure 5 is a graph illustrating an example of the rotational speed of the main spindle 144 as driven by the vector motor 168 and flywheel shaft 200 in the operation of the tool 230 of Figure 3.

DETAILED DESCRIPTION OF THE INVENTION

[0035] In recent years, there has been a desire for the acceleration of construction machines in order to do more work in less time. When working on a work piece 150, it is typically necessary to wait until the rotation of the main spindle 144 for the workpiece 150 reaches the speed required to cut the material.

[0036] Reduction in the startup time can significantly reduce the total cycle time required for processing a work piece. Using the example above, if the startup time can be reduced to 2 seconds, then one cycle time will be 12 seconds, thus the total processing time will be 240 seconds. The total processing time would be reduced by approximately 20%. In ongoing machining operations, this time reduction represents a significant economic advantage. [0037] Also, energy efficient movement is generally desired. For reducing the acceleration time, changing the main motor to a higher output motor is one approach, but this approach will typically require more energy for rotation at times when there is not a need for a high output. Another approach is to provide a flywheel 84, 86 and an acceleration motor 64, as described in Figure 2. In the configuration of Figure 2, however, the flywheel 84, 86 and acceleration motor 64 are mounted on the same shaft 76, which requires that both the acceleration motor 64 and the flywheel 84, 86 rotate at the same speed at all times.

[0038] In the device described in Figure 2 of U.S. Patent No. 5,673,467, the acceleration motor 64 always gives out a constant rotation to the flywheel 84, 86, which is attached to the motor 64 so that it needs to constantly rotate with the movement of the machine tool spindle 44. However, the flywheel 84, 86 does not always need to rotate at a constant speed, so the energy required to energize the acceleration motor 64 to rotate the flywheel 84, 86 may be wasted.

[0039] In one exemplary embodiment of the present invention, an acceleration motor 164 and flywheel 206 are coupled to the machine tool 146 described in U.S. Patent No. 5,673,467 using a one way clutch 204 disposed between the two devices. The flywheel 206 is attached to a flywheel shaft 200. One way clutch 204 permits the flywheel shaft 200 to be driven in one direction of rotation and to rotate freely when the flywheel shaft 200 rotates faster than the acceleration motor 164, i.e. when the acceleration motor 164 is turned off. The acceleration motor 164, e.g. an induction motor, is coupled to the flywheel shaft 200 by a set of transmission belts 212 through a pulley 208 integrated with the one way clutch 204 of the flywheel shaft 200.

[0040] The flywheel shaft 200 is coupled to the main spindle shaft 144 by another set of transmission belts 214, where a computer controlled clutch 202, which may be a CNC clutch, controls whether the flywheel shaft 200 is engaged to drive the main spindle shaft 144. The CNC clutch 202 may be an automotive clutch, which is relatively inexpensive and easy to replace when it wears out. The CNC clutch 202 is controlled by a control means 182, such as a main CNC computer for the machine tool 230, and is engaged to accelerate a main spindle 144. [0041] In an embodiment of the present invention, the acceleration motor 164 and the flywheel 206 are not directly attached, but are attached together with at least one transmission belt 212. The flywheel 206 and one way clutch 204 are mounted to a flywheel shaft 200 with a pulley 208 to which the belt 212 from the acceleration motor 164 is engaged. The flywheel 206 has a speed sensor 210 that provides a speed signal to the control means 182. In this embodiment, the acceleration motor 164 will be activated by the control means 182 to rotate whenever the flywheel's 206 rotation speed goes below a predetermined or programmed minimum rotation speed to accelerate the flywheel 206 to another higher predetermined or programmed rotation speed. See Figure 4 and the related discussion below for an example of operation of the acceleration motor 164.

[0042] The flywheel shaft 200 is coupled to the main spindle shaft 144 through another pulley 218. Between the flywheel shaft 200 and the main spindle shaft 144, there is, in this example, a one-way CNC clutch 202 that can be engaged in response to a signal from the control 182 to transmit the rotation of the flywheel shaft 200 and the flywheel 206 to the main spindle shaft 144. By making the CNC clutch 202 a one way clutch, the main spindle shaft 144 can rotate faster than the flywheel shaft 200. Other embodiments may dispose the one way clutch function into other elements, such as the pulley 190 connected to the main spindle shaft 144.

[0043] The CNC clutch 202 is controlled by the control means 182 to engage the flywheel shaft 200 to drive the main spindle shaft 144 up to a predetermined operating rotation speed. Whenever the computer controlled process calls for the main spindle 144 to be accelerated, the control means 182 will engage the CNC clutch 202 and the flywheel's 206 rotational energy will be transmitted to the main spindle 144. See Figure 5 and the related discussion below for an example of operation of the CNC clutch 202 to accelerate the main spindle 144.

[0044] Because the one way clutch 202 can be used to disengage the flywheel shaft 200 from the main spindle shaft 144, the flywheel shaft 200 does not need to be maintained at a constant rotational speed by the acceleration motor 164. Therefore, the acceleration motor 164 does not need to be constantly energized and, therefore, can be deactivated to conserve electric power. [0045] Also, because the main spindle 144 is accelerated by the flywheel 206, the assisting or acceleration motor 164 used to rotate the flywheel 206 may be a lower output motor than might otherwise be required, e.g. a 40 to 60 horsepower (hp). This is because the flywheel 206 may be accelerated over a longer period of time to its predetermined operating speed by the acceleration motor 164. This can also lower the energy requirements of the system and may allow a less expensive acceleration motor 164 to be used.

[0046] In a lathe processing example, the material to be worked on will be attached to the lathe's processing spindle's chuck 148. The processing spindle 144 will be stopped first to attach the workpiece material 150 and then the computer controlled processing will begin. The main spindle 144 is accelerated from 0 RPM to a high speed, e.g. 5,000 to 8,000 RPM. In many conventional machine tools, the time required to reach the high speed rotation may be 5 - 6 seconds. In the embodiment described herein, the spindle acceleration time may be reduced, e.g. by Vi to ¹A.

[0047] The assisting or induction motor 164 used for acceleration of the spindle 144, the speed sensor for the flywheel 210, and the clutch 202 that conducts the rotation in between the flywheel 206 and the main spindle 144 that is controlled by an electric signal, may all be interfaced or controlled by the main computer 182 used by the machine tool 230 itself.

[0048] Figure 4 is a graph of rotational speed illustrating one example of the operation of the tool 230 of Figure 3. When cutting a work piece 150, it is typically desirable that the work piece 150 attached to the chuck 148 should rotate at a speed of at least 5000 rpm in order to cut the work piece. During the cutting process, the rotational speed of the work piece 150 attached to the chuck 148 will decrease in speed due to a number of factors, such as gravity, various sources of friction, resistance when cutting, the volume or hardness of the work piece 150 material, or that the spindle 144 rotates in the opposite direction.

[0049] In the example of Figure 4, the machine 230 of Figure 3 is adapted to be a CNC lathe that begins operation from a dead stop, i.e. 0 RPM shown at point 240. In this example, the control means 182 is configured to accelerate the lathe to an operating speed of 6000 rpm, i.e. Point A 242, and prevent the rotation of the main spindle 144 from dropping below a minimum operational speed of 5000 rpm, i.e. Point B 244, during a cutting operation. In the conventional device 10 shown in Figure 1, the CNC controlled vector motor is used to maintain the main spindle between 5000 and 6000 rpm, which may consume a lot of power. In the machine 230 of Figure 3, the acceleration or induction motor 164 is activated by the controller 182 to accelerate the flywheel shaft 200 to 6000 rpm when the flywheel shaft 200 reaches 5000 rpm and is otherwise deactivated to conserve electric power. Also, the induction motor 164 is typically less expensive than the vector motor 168.

[0050] In Figure 4, the time interval required for the vector motor 168 to bring the main spindle 144 up to the operating speed, i.e. Point A 242, is shown as "Time A" 250. During the cutting process, the main spindle 144, which was brought up to 6000 rpm, decreases in speed as shown in time interval "Time B" 254. The time interval it takes the induction motor 164 to bring the spindle 144 to 6000 rpm is shown as "Time C" 256. The induction motor 164 is engaged when the speed reaches Point B 244, e.g. 5000 rpm, in order to accelerate the main spindle 144 to 6000 rpm.

[0051] Figure 5 is a graph illustrating the rotational speed of the main spindle shaft 144 of Figure 3 in another example of the operation of the machine 230 of Figure 3. As noted above, the main spindle 144 is typically stopped in order to attach a work piece 150 to a chuck 148 on the main spindle 144 in order to process the work piece 150. The main spindle 144 must then be accelerated from 0 RPM point 260 to the desired operating speed, which is 6000 RPM in this example. In many conventional devices, the vector motor alone is used to accelerate the main spindle, which may require a significant period of time relative to the actual cutting or processing time for the work piece. A curve for an acceleration using the vector motor alone 262 is shown in Figure 5.

[0052] In this example, the acceleration motor 164 is used to drive the flywheel shaft 200 to 5000 RPM and is engaged whenever the flywheel shaft 200 rotation drops to 4000 RPM. This permits a slower and less expensive induction motor to be used for the acceleration motor 164. In order to accelerate the main spindle shaft 144, the control 182 engages the CNC clutch 202 in order to transmit the rotational momentum of the flywheel 206 to the main spindle 144. In this example, the CNC clutch 202 is engaged until the main spindle 144 reaches 5000 RPM, which is the top speed of the flywheel shaft 200. Note that the vector motor 168 may also be engaged during this period to increase acceleration of the main spindle shaft 144. Alternatively, only the flywheel shaft 200 may be used to accelerate the main spindle shaft 144 to 5000 RPM. Note that the acceleration motor 164 may engage if the flywheel shaft 200 speed drops to 4000 RPM during the acceleration cycle.

[0053] Once the main spindle shaft 144 reaches 5000 RPM, the vector motor 168 accelerates the main spindle shaft 144 to 6000 RPM. Figure 5 includes a curve 264 illustrating acceleration using the flywheel shaft 200 to accelerate the main spindle shaft 144. Note that the time required to accelerate the main spindle shaft is significantly reduced in this example.

[0054] In another embodiment, a second CNC clutch may be included that permits the rotation of the main spindle shaft 144 to be contra llab Iy transmitted to the flywheel shaft 200. In this embodiment, the control 182 engages the second CNC clutch 202, which is not a one way clutch in this embodiment, to decelerate the main spindle shaft 144, e.g. from 6000 RPM to 5000 RPM, by transferring the rotation of the main spindle shaft 144 to the flywheel shaft 200. In another embodiment, the second CNC clutch 202 may include a one way clutch that permits the main spindle shaft 144 to rotate freely independent of the flywheel shaft 200 when the second CNC clutch is not engaged.

[0055] In still another embodiment, additional energy from the deceleration of the spindle 144 is recovered for use in the machine tool 230. In many conventional devices, the vector motor 168 is configured to switch to a generation mode in order to brake the main spindle shaft 144. The electric power produced in the generation mode is typically dissipated as heat using a heat element. In this embodiment, the electric power produced in the generation mode is used to charge an energy store, such as a battery. For example, a regenerative braking system used in hybrid automobiles may be adapted for this purpose. The stored energy is then used to power other components of the machine tool 230. For example, the stored energy may be used to power the control means 182. By way of another example, the stored energy may be used to power the acceleration motor 164.

[0056] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. [0057] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0058] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A computer controlled machine tool assembly, the assembly comprising: a rotatable spindle (150) attached to a main spindle shaft (144); a computer controlled vector motor (168) coupled to the main spindle shaft and configured to control rotation of the main spindle shaft under computer control (182); a flywheel shaft (200) attached to a flywheel (206) and having a speed sensor (210) for sensing a rotational speed of the flywheel shaft, the flywheel shaft being coupled to the main spindle shaft by a first pulley (218) through a computer controlled clutch (202), where the computer controlled clutch is configured to engage the flywheel shaft to the main spindle shaft when activated under computer control; and an acceleration motor (164) coupled to the flywheel shaft through a second pulley (208) and a one way clutch (204), where the acceleration motor is activated under computer control responsive to the rotational speed of the flywheel shaft sensed by the speed sensor.

2. The computer controlled machine tool assembly of claim 1, where the computer controlled clutch (202) further comprises a one way computer controlled clutch.

3. The computer controlled machine tool assembly of claim 1, where the computer controlled clutch (202) is further configured to be engaged to decelerate the main spindle shaft (144) under computer control (182).

4. A method for controlling a rotational spindle in a machine tool, the method comprising the steps of: coupling a vector motor (168) to a main spindle shaft (144) attached to the rotational spindle (150); coupling a flywheel shaft (200) to the main spindle shaft through a computer controlled clutch (202); coupling an acceleration motor (164) to the flywheel shaft through a one way clutch mechanism; sensing (210) a rotational speed of the flywheel shaft; responsive to the rotational speed of the flywheel shaft being below a first speed, activating the acceleration motor under computer control (182); responsive to the rotational speed of the flywheel shaft reaching a second speed, deactivating the acceleration motor under computer control (182); and activating the computer controlled clutch (202) under computer control (182) to accelerate the main spindle shaft (144).

5. The method of claim 4, the method further including the step of activating the computer controlled clutch (202) under computer control (182) to decelerate the main spindle shaft (144).

6. The method of claim 4, wherein the step of coupling a flywheel shaft (200) to the main spindle shaft through a computer controlled clutch (202) further comprises coupling the flywheel shaft (200) to the main spindle shaft through a one way computer controlled clutch (202).