Poly-actuator

• US 20160336878A1
• Filed: 05/10/2016
• Published: 11/17/2016
• Est. Priority Date: 05/11/2015
• Status: Abandoned Application

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: TORRES, James, ASADA, Haruhiko Harry
• Application Number:
  US15/150,724
• Publication Number:
  US 20160336878A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H02N 2/02 producing linear motion, e.g. actuators; Linear positioners ; Linear motors
• CPC Class Codes: H02N 2/043 Mechanical transmission means, e.g. for stroke amplification

Abstract

Similar to combustion engines including multiple cylinders engaged with a crankshaft, multiple piezoelectric stack actuators (PSA) engaged with a common output rod can produce smooth, long stroke motion with desired properties. In particular, when equally spaced multiple units are arranged to push sinusoidal gear teeth on the output rod, the system exhibits unique collective behaviors thanks to “harmonic” effects of the multiple units. For example, although the force-displacement characteristics of individual units are highly nonlinear, the undesirable nonlinearity, including singularity, may be eliminated. Here it presents harmonic analysis, design, and control of a class of actuators consisting of multiple driving units engaged with a sinusoidal transmission, termed a harmonic poly-actuator. Through theoretical analysis, it is obtained 1) conditions on the unit arrangement to eliminate their nonlinearity from the output force, 2) control algorithms for coordinating the multiple units to generate a commanded force with desired force-displacement characteristics, and 3) a method for compensating for output force ripples due to possible misalignment and heterogeneity of individual units. The control algorithms are implemented on a prototype harmonic poly-actuator with six units of PSAs. Experiments demonstrate the unique features of the poly-actuator exploiting inherent redundancy and harmonic properties of the system.

Claims

1. A poly-actuator comprising:

an output unit having one or more cam portions; and

a plurality of nonlinear reciprocating actuators each of which has a follower mechanism connected to the one or more cam portions;

wherein the cam portions are formed by smooth periodically curved surfaces which guide rotational centers of the follower mechanisms along a sinusoidal trajectory with respect to a motion of the output unit,

each of the nonlinear reciprocating actuators has nonlinearity in output force-displacement characteristics,

the nonlinear reciprocating actuators are equally spaced in terms of a phase of the sinusoidal trajectory,

a total distance obtained by multiplication of the number of the nonlinear reciprocating actuators and an equal interval between the nonlinear reciprocating actuators is equal to a multiple of a wave length of the sinusoidal trajectory,

the equal interval is not equal to any multiple of the wave length,

the output force has a nonlinear stiffness term including a k-th order term,

if k is odd, orders of harmonic components of the sinusoidal trajectory in the output force consists of even numbers in 2 to k+1, and if k is even, orders of the harmonic components in the output force consists of odd numbers in 1 to k+1, and

multiples of the number of the nonlinear reciprocating actuators do not match the orders of the harmonic components in the output force.

2. The poly-actuator according to claim 1,

wherein, if the nonlinear stiffness term consists of a 3rd order term and if the number of the nonlinear reciprocating actuators is 2, 3, or 4, all of the harmonic components are suppressed.

3. The poly-actuator according to claim 1,

wherein the output force has a nonlinear input-induced force term including a q-th order term,

an input signal to each of the nonlinear reciprocating actuators includes at least an L-th order harmonic component of the sinusoidal trajectory,

the harmonic component in the input signal has a phase shift between the nonlinear reciprocating actuators,

the phase shift is equal to the equal interval between the nonlinear reciprocating actuators,

if q is odd and L is even, orders of the harmonic components in the output force consists of even numbers in absolute values of L to l+L+q and in −

L to 1−

L+q,

if q is odd and L is odd, orders of the harmonic components in the output force consists of odd numbers in absolute values of L to 1+L+q and in −

L to 1−

L+q,

if q is even and L is even, orders of the harmonic components in the output force consists of odd numbers in absolute values of 1+L to 1 + L+q and in 1−

L to 1−

L+q,

if q is even and L is odd, orders of the harmonic components in the output force consists of odd numbers in absolute values of 1+L to 1+L+q and in 1−

L to 1−

L+q, and

multiples of the number of the nonlinear reciprocating actuators do not match the orders of harmonic components in the output force.

4. The poly-actuator according to claim 3,

in a case where the input-induced force term consists of a 3rd order term, the input signal consists of a 2nd order harmonic component, and the number of the nonlinear reciprocating actuators is 3 or 5, or

in a case where the input-induced force term consists of a 4th order term, the input signal consists of a 3rd order harmonic component, and the number of the nonlinear reciprocating actuators is 5,

all of the harmonic components other than 0th order harmonic component in the output force are suppressed.

5. The poly-actuator according to claim 3,

in a case where the input-induced force term consists of a 3rd order term, the input signal consists of a 3rd order harmonic component, and the number of the nonlinear reciprocating actuators is 2, 4, or 6, or

in a case where the input-induced force term, consists of a 4th order term, the input signal consists of a 2nd order harmonic component, and the number of the nonlinear reciprocating actuators is 2, 4, or 6,

all of the harmonic components in the output force are suppressed.

6. The poly-actuator according to claim 3,

wherein at least one of higher order harmonic components is superposed with respect to the L-th order harmonic component in the input signal,

an amplitude and/or a phase shift of the at least one of higher order harmonic components is controlled, and

a frequency of the superposed harmonic component is equal to a frequency to be suppressed.

7. The poly-actuator according to claim 3,

wherein at least one of higher order harmonic components is superposed with respect to the L-th order harmonic component in the input signal, and

an order of the at least one of higher order harmonic components is an odd number multiple of L.