# US 9,752,643 B2 · Negative stiffness system for gravity compensation of micropositioner

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- Number: US 9,752,643 B2
- Document ID: US9752643B2
- Status: Granted
- Kind: B2
- Application number: 14/652,055
- Filed: 2013-12-06
- Published: 2015-12-24
- Granted: 2017-09-05
- Earliest claimed: 2012-12-12
- Assignees: Shanghai Micro Electronics Equipment Co., Ltd.; Tsinghua University
- Applicants: Shanghai Micro Electronics Equipment Co., Ltd.; Tsinghua University
- Inventors: Yu Zhu; Ming Zhang; Zhao Liu; Rong Cheng; Jing Wang; Li Tian; Dengfeng Xu; Kaiming Yang; Jinchun Hu; Wensheng Yin; Haihua Mu; Hao Liu; Chuxiong Hu
- Web page: https://patentgrep.com/patent/US9752643B2

## CPC

- F16F 15/067: using only wound springs
- G03F 7/70: {Microphotolithographic exposure; Apparatus therefor (photo-masks G03F1/00)}
- G03F 7/70716: {Stages}
- G03F 7/70816: {Bearings}
- G03F 7/709: {Vibration, e.g. vibration detection, compensation, suppression or isolation}
- F16F 2228/063: Negative stiffness
- F16F: SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

A negative stiffness system for gravity compensation of a micropositioner of wafer table in lithography machine, characterized in that, the negative stiffness system includes at least three sets of quasi-zero stiffness units, each of the sets of quasi-zero stiffness units comprises a pair of negative stiffness springs and a positive stiffness spring, the positive stiffness spring is vertically positioned, the pair of negative stiffness springs are obliquely and symmetrically positioned at two sides of the positive stiffness spring, upper ends of the negative stiffness springs and the positive stiffness spring are connected together and fixed to the bottom surface of a rotor of the micropositioner, and lower ends of the negative stiffness springs and the positive stiffness spring are connected to a base, respectively. The system reduces the stiffness in vertical direction and prevents the influence of permanent magnet on its surroundings, while improving the bearing capacity.

## Claims

### Claim 1

A negative stiffness system for gravity compensation of a micropositioner, wherein the negative stiffness system includes at least three sets of quasi-zero stiffness units, each of the sets of quasi-zero stiffness units comprises a pair of negative stiffness springs and a positive stiffness spring, the positive stiffness spring is vertically positioned, the pair of negative stiffness springs are obliquely and symmetrically positioned at two sides of the positive stiffness spring, upper ends of the negative stiffness springs and the positive stiffness spring are connected together and fixed to a bottom surface of a rotor of the micropositioner, and lower ends of the negative stiffness springs and the positive stiffness spring are connected to a base, respectively,
wherein an initial angle θ0 of each of the negative stiffness springs with respect to a horizontal plane satisfies the following specific stiffness ratio αQZS of each of the negative stiffness springs to the positive stiffness spring at a quasi-zero stiffness point;
α
QZS
=
γ
2
⁢
(
1
-
γ
)
,
wherein, the stiffness ratio αQZS is k0/kv;
L0: an initial length of each of the negative stiffness springs;
L: a length of each of the negative stiffness springs that is deformed;
γ: cosine of the initial angle θ0 of each of the negative stiffness springs, defined as γ=cos θ0;
α: a length of projection of each of the negative stiffness springs in a horizontal direction, defined as α=L cos θ0;
k0: a stiffness of each of the negative stiffness springs; and
kv: a stiffness of the positive stiffness spring,
wherein the base includes a first sidewall portion, a second sidewall portion, and a middle portion, the middle portion being disposed between the first sidewall portion and the second sidewall portion to connect the first and second sidewall portions,
wherein each of the lower ends of the negative stiffness springs are connected to an inner surface of a corresponding one of the first and second sidewall portions, and
wherein the lower end of the positive stiffness spring is connected to a top surface of the middle portion.

### Claim 2 (depends on 1)

The negative stiffness system according to claim 1, wherein when the negative stiffness system comprises three sets of quasi-zero stiffness units, the three sets of quasi-zero stiffness units are arranged in a triangle, and
wherein when the negative stiffness system comprises four sets of quasi-zero stiffness units, the four sets of quasi-zero stiffness units are arranged in a rectangle.

### Claim 3 (depends on 1)

The negative stiffness system according to claim 1, wherein the upper ends of the negative stiffness springs and the upper end of the positive stiffness spring are directly connected together.