UNI-TAP U.S. PATENT
COMPACT MECHANISM FOR CREATING SIMULTANEOUS
ROTARY AND LINEAR MOTION
BACKGROUND OF THE INVENTION
This invention relates to machine tools and more particularly. compact components for machine tools which create simultaneous linear and rotary movement of tools or workpieces.
A typical machining operation. such as drilling or tapping. requires that a cutting tool. such as a drill or tap, be rotated at a predetermined speed and advanced at a predetermined feed rate toward the workpiece in order to perform the machining operation. In conventional production environments. it is desirable to perform the operation as quickly as possible to minimize idle time and reduce costs. Consequently, it is important that the tool approach the workpiece at as high a feed rate as possible until just prior to contact with the workpiece and after the operation is completed, that the tool retract from the workpiece at as high a feed rate as possible. During machining, the rotational speed and feed rate of the tool are chosen to achieve optimal cutting performance and minimal tool wear. Unfortunately, conventional machine tools generally do not have a wide dynamic range of feed rates which are effective to reduce approach and retract times and thus minimize idle time.
Conventional machine tools typically include an electric, hydraulic or pneumatic motor which is connected either directly or by gears or belts, to a drive shaft to produce rotary motion. The drive shaft, the motor and any intervening transmission is then coupled to a pneumatic or hydraulic cylinder or other linear actuator to provide the linear motion necessary for the desired feed rates. A chuck or other tool holding device can be coupled to the drive shaft for mounting a tool or workpiece. Other prior art devices. such as U.S. Pat. No. 3.407.680 to Westrnoreland, utilize two motors and a drive shaft to produce linear motion. One motor drives a ball screw engaging a helical race on one portion of the drive shaft to produce linear motion. The second motor drives a ball spline engaging a spline on a separate portion of the drive shaft to increase the rational speed of the shaft, with the net effect to increase the dynamic range of linear motion of the shaft. The end of the drive shaft is typically fitted with a device which transmits linear motion but does not transmit the rotary motion of the shaft. Because the helical race and the spline are on separate portions of the drive shaft, these devices are not compact and have a limited range of linear motion.
One of the significant disadvantages of the prior art devices is that they are large and bulky. Because of their size. they require a large supporting frame, they are difficult to manipulate during use and they limit the size of tools and worlcpieces that can be used. In addition, the prior art devices are mechanically and electrically complex, therefore have poor reliability and are difficult to maintain and repair. In addition, attempts to produce compact light weight designs have resulted in devices that are less accurate and have a limited range of rotational speeds and feed rates.
Accordingly. it is an object of this invention to provide an 5 improved mechanism for creating simultaneous rotary and linear motion.
It is another object of the invention to provide a compact mechanism for creating simultaneous rotary and linear motion.
It is yet another object of the invention to provide an improved mechanism for creating simultaneous rotary and linear motion which has a greater dynamic range of rota- tional speeds and feed rates.
SUMMARY OF THE INVENTION
The foregoing objects are accomplished in accordance with the present invention by providing a first drive motor for imparting a linear motion to an output shaft and a second drive motor for imparting a rotary motion to the output shaft. The output shaft can include a chuck or other tool holding device. A controller can also be provided to independently control the speeds to the motors and thus control rotational speed and linear feed of the shaft.
In one embodiment, the first drive motor includes a rotor and a stator. The stator of the first motor is coupled to the stator of the second drive motor and can include a mounting element for mounting the device on a machine tool as a drilling or tapping unit or a gripping element for holding a workpiece. The rotor is coupled to a first transmitting element which converts the rotary motion of the rotor to linear motion and imparts that linear motion to the output shaft while permitting the shaft to rotate.
The second drive motor also includes a rotor and a stator. The stator of the second motor is coupled to the stator of the first drive motor. The rotor is coupled to the second transmitting element which imparts rotary motion to the output shaft while permitting the shaft to move axially.
In another embodiment, the first drive motor includes a rotor and a stator. The rotor of the first motor is coupled to a first transmitting element which converts the rotary motion of the rotor to linear motion and imparts that linear motion to the output shaft. The output shaft can include a mounting or gripping element for holding a tool or workpiece. The stator of the first motor is coupled to the rotor of a second drive motor and a second transmitting element.
The second drive motor also includes a rotor and a stator. The stator can include a mounting element for mounting the device on a machine tool. The rotor of the second motor is coupled to the stator of the first drive motor and the second transmitting element. The second transmitting element irnputs rotary motion to the output shaft while permitting the shaft to move axially.
In the second embodiment. the first drive motor is rotated by the second drive motor and therefore brushes or slip rings can be utffized to provide power and control signals to the motor.
In either embodiment, the output shaft can include at least a portion which can be engaged by both the first transmitting element and the second transmitting element and therefore permits more linear travel of the output shaft per unit length of the device. This results in a simple and compact mechanism for producing both simultaneous linear and rotary motion.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, may be more fully understood from the following description. when read together with the accompanying drawings in which:
FIGURE 1 shows a drilling device having a compact mecha- nism for creating simultaneous linear and rotary motion in accordance with one embodiment of the invention;
FIGURE 2 shows a machining center having several turning tools arranged around a rotary table. each includes a com- pact mechanism for creating simultaneous linear and rotary motion in accordance with one embodiment on the present invention.
FIGURE 3 shows an alternate embodiment of a compact mechanism according to the present invention in the form of an apparatus for screwing the lid onto a jar.
FIGURE 4 shows a lathe having a compact mechanism for creating simultaneous linear and rotary motion in accordance with one embodiment of the invention.
FIGURE 5 is a diagrammatic cross-sectional view of a com- pact mechanism of FIG. I in accordance with one embodi ment of the invention.
FIGURE 6 is a diagrammatic cross-sectional view of a compact device in accordance with another embodiment of the invention.
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