scholarly journals Flexure wheels for spacecraft attitude control

2021 ◽  
Author(s):  
Patrick Fluckiger ◽  
Simon Henein ◽  
Ilan Vardi ◽  
Hubert Schneegans ◽  
Loïc Tissot-Daguette
Keyword(s):  
Angular Momentum ◽  
Attitude Control ◽  
Compliant Mechanism ◽  
The Body ◽  
Degree Of Freedom ◽  
Centre Of Mass ◽  
Angular Rotation ◽  
Flexure Mechanism ◽  
Fixed Axis ◽  
Two Degree Of Freedom

This paper presents innovative mechanisms capable of advantageously providing attitude control for spacecrafts. These new mechanisms, which we have named flexure wheels, are the dynamic equivalent of a rotating wheel and can be entirely implemented with flexures.A reaction wheel is a well known device for controlling the orientation of spacecrafts. It consists in a motorised fly-wheel which is placed within the spacecraft. To set the wheel into angular rotation, a torque is applied to the wheel which in response applies the opposite torque back to the spacecraft, according to Newton's third law. This reaction torque is how the spacecraft rotates in order to control its orientation. In order to enable this wheel to rotate around a fixed axis, several methods have been implemented such as ball bearings, which suffer from frictional losses and imperfections which lead to vibrations and failure, as well as magnetic bearings which do not suffer from these issues but have an increased power consumption and complexity.The subject of this paper is to introduce alternative mechanisms that are able to produce the same constant angular momentum as a rotating wheel, but which do not suffer from the above defects.In order to reach this goal, our inventions use flexure mechanisms to produce the required constant angular momentum. Note that the term flexure mechanism is exactly equivalent to compliant mechanism. The difficulty in this task is that flexures only have a limited stroke making it virtually impossible for a flexure bearing wheel to rotate around a fixed axis with constant angular momentum. We therefore found alternate methods for generating angular momentum by using flexure mechanisms.Two methods are presented in this paper. The first consists of a rigid body whose centre of mass has a circular trajectory around a fixed point, but the body does not rotate around its centre of mass. The body moves in translation and acts dynamically as a point mass, and thereby generates angular momentum in a constant direction. The second consists of two bodies rotating around their centres of mass, but whose total angular momentum lies in a fixed direction. The first method was successfully exploited in the IsoSpring project whose goal was to introduce new two degree of freedom oscillators in mechanical clocks and watches, in order to remove their traditional escapement mechanism. The second mechanism is also inspired from the IsoSpring project where a sphere oscillating around its centre of mass provided a two degree of freedom oscillator less sensitive to the direction of gravity.The paper presents flexure wheel designs along with their implementations. Moreover, methods to control the uniform circular motion are presented, among which a novel flexure bearing which restricts the motion of a body to translation on a circular orbit. Two prototypes were successfully built and tested. Finally, qualitative results from this proof of concept are presented.

Decentralized Control of Active Vehicle Suspensions With Preview

1995 ◽  
Vol 117 (4) ◽  
pp. 478-483 ◽  
Author(s):  
Aleksander Hac´
Keyword(s):  
Decentralized Control ◽  
The Body ◽  
Degree Of Freedom ◽  
Vehicle Model ◽  
Fast Subsystem ◽  
Interconnected System ◽  
Single Degree Of Freedom ◽  
Vehicle Suspensions ◽  
Slow Subsystem ◽  
Two Degree Of Freedom

In this paper, decentralized control of active vehicle suspensions with preview of road irregularities is considered using a two-degree-of-freedom vehicle model. It is shown that by taking advantage of the separation between the eigenvalues of the slow subsystem representing the body mode, and the fast subsystem corresponding to the wheel mode, the design of the preview controller can be decoupled. Since decentralized preview controllers are synthesized independently for two single-degree-of-freedom systems, analytical solutions are obtained. The results of the analysis and simulations demonstrate that the performance of the system with the proposed controller is comparable to that of the optimal preview controller based on a fully interconnected system.

Attitude Control of an Artificial Satellite Using H ∞ and Two-Degree-of-Freedom Control -On-Orbit Experiments Using ETS-VI-

1996 ◽  
Vol 29 (1) ◽  
pp. 7516-7521
Author(s):  
Y. Chida ◽  
Y. Yamaguchi ◽  
H. Soga ◽  
T. Kida ◽  
I. Yamaguchi ◽  
...  
Keyword(s):  
Attitude Control ◽  
Artificial Satellite ◽  
Degree Of Freedom ◽  
Two Degree Of Freedom

Circuit and Branch Rectification of the Spatial 4C Mechanism

2000 ◽  
Author(s):  
Pierre M. Larochelle
Keyword(s):  
Rigid Body ◽  
Finite Sequence ◽  
The Body ◽  
Degree Of Freedom ◽  
Motion Generation ◽  
Moving Body ◽  
In Series ◽  
Simply Connected ◽  
Two Degree Of Freedom ◽  
Physical Dimensions

Abstract Spatial 4C mechanisms are two degree of freedom kinematic closed-chains consisting of four rigid links simply connected in series by cylindrical(C) joints. In this work we are concerned with the design of spatial 4C mechanisms which move a rigid body through a finite sequence of prescribed locations in space. This task is referred to as rigid-body guidance by Suh and Radcliffe (20) and as motion generation by Erdman and Sandor (6). When 4C mechanisms are synthesized for such a task, for example by utilizing Roth’s spatial generalization of Burmester’s planar methods (17; 18), the result is the physical dimensions which kinematically define the mechanism. However, the motion of the mechanism which takes the workpiece through the sequence of prescribed locations in space is not determined. In fact, it may be impossible for the mechanism to move the body through all of the desired locations without disassembling the mechanism. This condition is referred to as a circuit defect. Moreover, in some cases the mechanism may enter a configuration which requires an additional mechanical input to guide the moving body as desired. These are referred to as branch defects. This paper presents a methodology for analyzing spatial 4C mechanisms to eliminate circuit and branch defects in motion generation tasks.

On-orbit attitude control experiments using ETS-VI by control and two-degree-of-freedom control

1998 ◽  
Vol 6 (9) ◽  
pp. 1109-1116 ◽  
Author(s):  
Yuichi Chida ◽  
Hiroshi Soga ◽  
Yoshitake Yamaguchi ◽  
Takashi Kida ◽  
Isao Yamaguchi ◽  
...  
Keyword(s):  
Attitude Control ◽  
Degree Of Freedom ◽  
Two Degree Of Freedom

Design of a 2 DOF Prosthetic Ankle Using Coupled Compliance to Increase Ankle Torque

2012 ◽  
Author(s):  
Shuguang Huang ◽  
Joseph M. Schimmels
Keyword(s):  
Ankle Joint ◽  
Compliant Mechanism ◽  
Lower Leg ◽  
The Body ◽  
Degree Of Freedom ◽  
Spring Constant ◽  
Active Components ◽  
Active Behavior ◽  
Ankle Torque ◽  
Optimization Routine

Current passive prosthetic ankles are lighter, simpler, and less expensive than powered prosthetic ankles. These current passive designs, however, do not provide adequate torque at the instant when it is needed to propel the body forward. This paper presents a novel 2 degree of freedom (DOF) passive compliant prosthetic ankle that uses a network of conventional springs. One DOF allows the lower leg component to compress when the weight of the amputee is applied during walking. The second DOF allows rotation about the prosthetic ankle joint. The force generated along the leg during walking is converted into ankle torque used to propel the body forward during push-off. An optimization routine is used to select the stiffness values and connection locations of the springs used in the compliant mechanism. The optimization yields a design that generates a torque-deflection profile that is very similar to that of a natural ankle. The mechanism demonstrates apparent active behavior (negative spring constant) at the ankle during push-off without using active components.

A Patient-Mounted, Telerobotic Tool for CT-Guided Percutaneous Interventions

2008 ◽  
Vol 2 (1) ◽  
Author(s):  
Conor J. Walsh ◽  
Nevan C. Hanumara ◽  
Alexander H. Slocum ◽  
Jo-Anne Shepard ◽  
Rajiv Gupta
Keyword(s):  
Improve Patient Care ◽  
Cost Effective ◽  
The Body ◽  
Degree Of Freedom ◽  
Widespread Application ◽  
Ct Guided ◽  
Percutaneous Interventions ◽  
Order Of Magnitude ◽  
Plastic Parts ◽  
Two Degree Of Freedom

This paper describes Robopsy, an economical, patient-mounted, telerobotic, needle guidance and insertion system, that enables faster, more accurate targeting during CT-guided biopsies and other percutaneous interventions. The current state of the art imaging technology facilitates precise location of sites within the body; however, there is no mechanical equivalent to then facilitate precise targeting. The lightweight, disposable actuator unit, which affixes directly to the patient, is composed primarily of inexpensive, injection molded, radiolucent, plastic parts that snap together, whereas the four micromotors and control electronics are retained and reused. By attaching to a patient, via an adhesive pad and optional strap points, the device moves passively with patient motion and is thus inherently safe. The device’s mechanism tilts the needle to a two degree-of-freedom compound angle, toward the patient’s head or feet (in and out of the scanner bore) and left or right with respect to the CT slice, via two motor-actuated concentric, crossed, and partially nested hoops. A carriage rides in the hoops and interfaces with the needle via a two degree-of-freedom friction drive that both grips the needle and inserts it. This is accomplished by two rubber rollers, one passive and one driven, that grip the needle via a rack and pinion drive. Gripping is doctor controlled; thus when not actively being manipulated, the needle is released and allowed to oscillate within a defined region so as to minimize tissue laceration due to the patient breathing. Compared to many other small robots intended for medical applications, Robopsy is an order of magnitude less costly and lighter while offering appropriate functionality to improve patient care and procedural efficiency. This demonstrates the feasibility of developing cost-effective disposable medical robots, which could enable their more widespread application.

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