Miniature gear reduction unit driven by a silicon electrostatic wobble motor

Abstract

This work illustrates and explores one possibility to link watch fine mechanics to silicon-based actuators. A small scale microreduction module, a pinion-gear train, coupled to an electrostatic wobble motor (calculated power figure about 1 pW), is described. The motor parts are fabricated on silicon. Electrodeposition of nickel in a positive photoresist mould is used for the fabrication of the rotor (a 2").This last is flexible to permit verticallywobbling and is directly connected to a n output shaft. Functional operation of this microreduction unit was successful and demonstrated the possibility to output torque from a n electrostatic wobble motor. Measurements and observations of rotor elasticity and geardaxle characteristics are presented and discussed in view of a possibly improved design.

An electrostatic lower stator axial-gap polysilicon wobble motor. I. Design and modeling

“…2) Dynamic Behavior: The velocity of a point on the rotor can be found from the time derivative of its position (15). From the velocity, the kinetic energy of the rotor is easily obtained (17) In this expression, the first term on the right is due to the motion of the center of the rotor, the second term is a result of the rotation of the rotor, and the last term is caused by the rocking motion of the rotor. From Hamilton's principle [20], using the expressions for the electrostatic coenergy and kinetic energy as given in (4) and (17), respectively, the equation of motion for the rotor can be found.…”

“…From the velocity, the kinetic energy of the rotor is easily obtained (17) In this expression, the first term on the right is due to the motion of the center of the rotor, the second term is a result of the rotation of the rotor, and the last term is caused by the rocking motion of the rotor. From Hamilton's principle [20], using the expressions for the electrostatic coenergy and kinetic energy as given in (4) and (17), respectively, the equation of motion for the rotor can be found. When additional terms are added to account for damping mechanisms, this yields sgn (18) where is the rotational inertia of the rotor, related to the contact point angle, given by (19) The rotational inertia of the rotor is mainly determined by its inertia about the rocking axes, which is represented by the last term on the right-hand side of (19).…”

“…The tilting, vertical, and radial rotor instabilities of this lower stator axial-gap design are constrained by the bearing and stator geometry. The larger rotor-to-stator overlap results in a larger torque generation and successful drive of a gear train has already been realized by a hybrid design based on electroplating and assembling techniques [17].…”

Examples of Silicon Based Microsystems

“…A coin flipped on a table rotates also slowly on itself Based on this principle, an electrostatic wobble motor has been fabricated for application in wristwatches [9].…”

A fabrication process for electrostatic microactuators with integrated gear linkages

“…Other examples of assembled devices that transfer mechanical power are magnetic micromotors, where Permalloy and polymethyl metacrylate (PMMA) parts are fabricated with sacrificial lithografie und galvano abformung (LIGA) techniques, which are subsequently assembled with submicron tolerances [2]. Axial-gap wobble motors have also been fabricated from electroplated nickel rotors that were coupled to miniature pinion and gear trains using assembling techniques [3]. Devices where mechanical linkages have been integrated with actuator fabrication are vibromotors, where a slider is driven by oblique impact of resonant comb structures [4], and a comb-drive-based microengine, where the linear motion of comb structures is converted into a rotary motion of an output gear by connecting rods [5].…”