Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
1998-10-14
2001-01-30
Bucci, David A. (Department: 3682)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C476S064000, C476S067000
Reexamination Certificate
active
06178836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positioning apparatus for positioning a slide body used in a precision machine such as, for example, an optical disc mastering machine or a semiconductor testing machine, and a frictional reciprocating drive mechanism used for reciprocatingly driving the slide body.
2. Description of the Prior Art
In a machine such as, for example, an optical disc mastering machine or a semiconductor testing machine, which requires a high precision, a pneumatic slide device in which a slide body is installed for reciprocating movement through an externally pressurized linear bearing assembly has hitherto been employed largely. For driving the slide body, a linear motor of a voice-coil type is generally employed and a closed loop control system is employed in which an interference laser measuring instrument or a linear scale is employed for a position detector. Also, in an apparatus such as, for example, the semiconductor testing machine, in which after having been positioned the slide body is required to be held in a static condition in order for a work to be observed, a ball screw is largely employed for driving the slide body.
It has, however, been found that the slide device utilizing the linear motor of the voice-coil type is of a completely non-contact design, the slide device tends to be adversely affected by an external disturbance. For this reason, improvement in resolution has hitherto been limited. On the other hand, the slide device utilizing the ball screw for driving the slide body, the presence of an error in shape of a helical groove and/or diameter of balls tends to result in fluctuation in speed so as to bring about a shaking motion of the slide body in a direction axially of a shaft.
Apart from the above, a frictional reciprocating drive mechanism comprising a main shaft adapted to be rotated and a roller held in a rolling contact with the main shaft and inclined a predetermined angle relative to the main shaft has been suggested as a device effective to accomplish a precise feed. However, even this frictional reciprocating drive mechanism is unable to accomplish a highly accurate drive of the main shaft, failing to achieve a precise positioning of the slide body, because of the presence of an influence brought about by a fluctuated rotation of the motor and/or a phase deviation occurring in a transmission system for transmitting the rotation of the motor to the main shaft.
In addition, the conventional externally pressurized linear bearing assembly has been found difficult to secure a sufficient rigidity of the bearing assembly and the lack of a sufficient rigidity tends to adversely affect the accuracy of positioning.
The apparatus in which the pneumatic slide device having the linear motor of the voice-coil type discussed above is utilized, or the apparatus in which the ball screw is utilized to drive the slide body, inherently involve a factor such as, for example, a yawing that tends to reduce the accuracy and, therefore, a highly accurate positioning is difficult to achieve.
Yet, since the accuracy of positioning is limited because of fluctuation in speed of movement of the slide body, a high density write-in is difficult to achieve where the pneumatic slide device is utilized.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been devised with a view to substantially eliminating the above discussed problems inherent in the prior art apparatuses and is intended to provide an improved frictional reciprocating drive mechanism including a main shaft and a plurality of rollers rollingly contacting the main shaft while oriented at a predetermined angle relative to the main shaft, wherein influence which would be brought about by a fluctuation of rotation of a rotatory drive source is minimized along with minimization of the phase deviation in the rotary drive transmission system to accomplish a highly accurate positioning.
Another important object of the present invention is to provide an improved positioning apparatus, which is less susceptible to deviation in speed to accomplish a stabilized feed and which is robust against an external disturbance enough to increase the resolution.
A further object of the present invention is to provide an improved positioning apparatus of the type referred to above, wherein the factor, such as a yawing, which leads to reduction in accuracy, is minimized; which is less susceptible to deviation in speed to accomplish a stabilized feed and which is robust against an external disturbance enough to increase the resolution.
In order to accomplish these and other objects of the present invention, the present invention according to one aspect thereof provides a frictional reciprocating drive mechanism which comprises a main shaft, a roller held in a rolling contact with an outer periphery of the main shaft and inclined at a predetermined angle relative to the main shaft, a slide body movable together with the roller that is moved as a result of rotation of the main shaft, a source of rotation for rotating the main shaft, and a reduction gear unit for transmitting the rotation of the source of rotation from a drive-side shaft to a friction wheel to thereby transmit the rotation of the source of rotation at a reduced speed to the main shaft.
According to the present invention, by rotating the main shaft, the roller rotates about the associated roller spindle in a direction substantially counter to the direction of rotation of the main shaft while oriented at a lead angle that is equal to the angle of inclination of the roller, accompanied by a frictional force developed between the roller and the main shaft. By those forces of friction between the roller and the main shaft, the slide body is driven axially of the main shaft. In such case, since the rotation of the rotatory drive source is transmitted to the main shaft after having been reduced in speed, any possible influence which would be brought about by fluctuation in rotation of the rotatory drive source on the accuracy of positioning of the slide body can be minimized. Also, transmission and reduction in speed of the rotation of the rotatory drive source are accomplished through the frictional contact between the drive-side shaft and the friction wheel and, therefore, no backlash occur, resulting in a highly accurate positioning of the slide body.
The frictional reciprocating drive mechanism of the structure described above may further comprises a displacement permitting support means for displaceably supporting the drive-side shaft so as to displace in a direction close towards and away from the friction wheel, and a pressure applying means for resiliently urging the drive-side shaft towards the friction wheel.
Application of the pressure to the drive-side shaft so as to urge the latter towards the friction wheel is effective to attain a stabilized frictional contact while absorbing an error in a direction radially of the friction wheel position, to thereby attain a further stabilized rotatory drive transmission.
Also, in this frictional reciprocating drive mechanism, a solid lubricant contacting an outer peripheral face of the friction wheel may be utilized so that a predetermined quantity of lubricant can be supplied to respective friction areas to accomplish a stabilized rotation for a substantially long period of time to secure a further stabilized operation. Accordingly, a further accurate positioning is possible. Also, since the solid lubricant is used, the possibility of fluctuation in rotation which would result from the intervention of a lubricant can be prevented unlike the standard grease.
In this frictional reciprocating drive mechanism, said roller is rotatably mounted on an outer periphery of a roller spindle through a circumferential row of rolling elements and the roller spindle is sandwiched from an axial direction between a fixed support and a pressing member both provided on the slide body. The fixed support and the pressing member include a spindle retaining means for r
Miyake Toru
Okada Manabu
Bucci David A.
Joyce William C
NTN Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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