End effector with force controlling mechanism

Abstract

A precision soft-touch end effector has a mounting plate attached to a robot arm. The plate supports a stepper motor. The output shaft of the stepper motor is connected through a spring to an elongated finger that slides in a central longitudinal slot of the plate and supports a first wafer gripping post, while on the end opposite to the first wafer gripping post the mounting plate pivotally supports two L-shaped fingers with a second and third wafer gripping posts on their respective ends. The mounting plate in combination with the first sliding finger and two pivotal fingers forms the end effector of the robot arm which is thin enough for insertion into a wafer-holding slot of a wafer cassette. The end effector is equipped with a mapping sensor for detecting the presence or absence of the preceding wafer, wafer position sensors for determining positions of the wafer with respect to the end effector, and force sensors for controlling the wafer gripping force. Several embodiments relate to different arrangements of gripping rollers and mechanisms for control of the gripping force and speed of gripping required for gripping the wafer with a soft and reliable touch.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] The present patent application is a divisional of pending U.S. patent application Ser. No. 09 / 944,605 filed by B. Kesil, et al. on Sep. 4, 2001 and entitled “Precision Soft-Touch Gripping Mechanism for Flat Objects” and also is related to U.S. patent application Ser. No. 10 / 719,411 filed by B. Kesil et al., on Nov. 24, 2003 which is entitled “Soft-Touch Gripping Mechanism for Flat Objects” and is a continuation-in-part of aforementioned U.S. patent application Ser. No. 09 / 944,605.FIELD OF THE INVENTION [0002] The present invention relates to the field of material handling equipment, in particular to end effectors used in semiconductor production, disk-drive manufacturing industries and the like for precision gripping, transportation and positioning delicate, thin and highly accurate flat objects such as semiconductor wafers, hard disks, etc. BACKGROUND OF THE INVENTION [0003] One of the major methods used at the present time in the sem...

AI Technical Summary

Benefits of technology

[0022] It is an object of the invention is to provide an end effector for handling flat thin objects, such as semiconductor wafers or glass substrates, with a predetermined or adjustable soft-touch gripping force. It is another object to provide an end effector that operates with high reliability. A further object is to provide end effectors with at least three edge gripping posts moving simultaneously in the same direction and stopped when a predetermined gripping forc

Problems solved by technology

This to some extent helped to reduce breakage, but did not solve the contamination problem.

However, these standards helped reduce, but did not eliminate, the confusion involved in the selection and application of robotic wafer handling.

Another compromise is the need to design semiconductor manufacturing equipment suitable for accepting a large variety of wafer sizes.

This adds unnecessary complexity to equipment design.

Recent transfer to 300-mm wafers, evolved new problems associated with much higher cost of a single wafer (up to several thousand dollars as compared with several hundred dollars for 200 mm wafers) and thus required higher accuracy and reliability of the wafer handling equipment.

Furthermore, transition to 300 mm wafers made the use of low vacuum unsuitable for holding and handling the wafers.

Another reason is that vacuum holders are not reliable for handling wafers of heavy weight.

Thus, the conventional vacuum end effectors appeared to be unsuitable for handling expensive, heavy, and hard-to-grip wafers of 300 mm diameter.

Using mechanical measurements or preliminary mapping procedures of location of the wafer in a cassette for precise positioning of the gripper relatively to the grasping points is a time consuming procedure that is difficult to perform in real conditions of the variety of wafer stages at wafer handling robotic lines.

However, such a robot arm is three-dimensional and is not applicable for handling thin flat objects, such as semiconductor wafers, located in a deep narrow slots of a multistack cassette of the type used for storing the wafers.

A disadvantage of the wafer handling system of Hollbrooks cons

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