METHOD AND APPARATUS FOR CABLE-DRIVEN ADAPTIVE VIBRATION CONTROL

• US 20190047705A1
• Filed: 08/10/2018
• Published: 02/14/2019
• Est. Priority Date: 08/11/2017
• Status: Active Grant

• Current Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Original Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Inventors: Diao, Xiumin, Xiong, Hao
• Granted Patent: US 10,640,210 B2
• Time in Patent Office: Days
• CPC Class Codes: B64C 2027/004 using actuators, e.g. active systems
• CPC Class Codes: B64C 27/001 Vibration damping devices
• CPC Class Codes: B64F 3/00 Ground installations specially adapted for captive aircraft
• CPC Class Codes: B64U 10/13 Flying platforms
• CPC Class Codes: B64U 2101/30 for imaging, photography or videography
• CPC Class Codes: B64U 2201/20 Remote controls
• CPC Class Codes: B64U 2201/202 using tethers for connecting to ground station
• CPC Class Codes: B64U 50/19 using electrically powered motors
• CPC Class Codes: G05D 1/0816 to ensure stability
• CPC Class Codes: G05D 1/0825 using mathematical models
• CPC Class Codes: G05D 1/085 to ensure coordination between different movements

Abstract

A vibration control system for an unmanned aerial vehicle (UAV) is disclosed. The system includes a base platform fixedly coupled to a UAV structure, a working platform coupled to the base platform by two or more cables at two or more connection points on the working platform, and two or more actuators positioned either on the base platform or the working platform, each actuator configured to receive a signal to adjust tension in a corresponding cable, wherein by adjusting tension in the two or more cables, natural frequency of the working platform can be adjusted in response to frequency of vibration experienced by the working platform in order to maintain a frequency ratio (FR) of the vibration frequency to the natural frequency at or above a predetermined value.

Claims

1. A vibration control drive system used in an unmanned aerial vehicle (UAV), comprising:

a base platform fixedly coupled to a UAV structure;

a working platform coupled to the base platform by two or more cables at two or more connection points on the working platform;

two or more actuators positioned either on the base platform or the working platform, each actuator configured to receive a signal to adjust tension in a corresponding cable; and

a first controller coupled to and adapted to control the two or more actuators, whereby two or more control signals are calculated for the two or more actuators based on a target position from a current position of the working platform according to one of (i) an open-loop configuration, (ii) a first closed-loop configuration utilizing velocity of the working platform as a feedback signal, or (iii) a second closed-loop configuration utilizing velocity of the working platform as a first feedback signal and the position information of the working platform as a second feedback signal.

2. The drive system of claim 1, wherein each of (i) the open-loop, (ii) the first closed loop, and (iii) the second closed loop configurations initially calculates the target pose vector of the working platform.

3. The drive system of claim 2, wherein the target pose vector is calculated based on

l₁=[l₁₁ l₁₂ . . . l_ln]^T,l_s=[l_s1 l_s2 . . . l_sn]^T, and l_e=[l_e1 l_e2 . . . l_en]^T whereby

l_li represents length of each of the two or more cables and which includes l_si which represents an inelastic portion and l_ei which represents an elastic portion,

l_s*=l₁*−

l_e where * denotes the target representation of the working platform, and is calculated based on

M{umlaut over (x)}+C{dot over (x)}+G=−

J^Tτ

where M represents inertia matrix,

C represents Coriolis matrix,

G represents gravity matrix,

J represents Jacobian matrix, and

τ

represents tension in the two or more cables, which yields n−

1 equations for n cable tension unknowns which can be solved for a tension solution, and where tension and the change in l_e are related based on

τ

=EA·

diag<sup>−

1</sup>(l_e)Δ

l_e, where

E represents Young'"'"'s modulus of elasticity of the elastic portion and A represents cross sectional area of each of the two or more cables, and

Δ

l_e represents extended length of each of the two or more cables and is defined by l₁−

l_s−

l_e and

6. The drive system of claim 1, further comprising one or more velocity sensors configured to provide velocity information of the working platform.

7. The drive system of claim 6, further comprising one or more position sensors configured to provide position information of the working platform.

8. The drive system of claim 1 further comprising a second controller configured to reduce vibration by adjusting tension in the two or more cables thereby adjusting the natural frequency of the working platform in response to frequency of vibration experienced by the working platform in order to maintain a frequency ratio (FR) defined as ratio of vibration frequency to the natural frequency of the working platform at or above a predetermined value.

9. The drive system of claim 1, further comprising one or more sensors configured to provide vibration information of the working platform.

10. The system of claim 9, the second controller configured to:

receive signals from the one or more vibration sensors;

determine the cable tension based on a previous calculated value of the natural frequency of the working platform and the FR;

provide signals for the two or more actuators to adjust the corresponding cables;

calculate a new natural frequency of the working platform; and

compare the FR to a predetermined value.

4. The drive system of claim 4, wherein the n−

1 equations and n unknowns can be solved for each tension of the two or more cables based on minimum norm least-squares.

5. The drive system of claim 5, wherein the Jacobian matrix is defined by

11. A vibration control system for an unmanned aerial vehicle (UAV), comprising:

a base platform fixedly coupled to a UAV structure;

a working platform coupled to the base platform by two or more cables at two or more connection points on the working platform; and

two or more actuators positioned either on the base platform or the working platform, each actuator configured to receive a signal to adjust tension in a corresponding cable;

wherein by adjusting tension in the two or more cables, natural frequency of the working platform can be adjusted in response to frequency of vibration experienced by the working platform in order to maintain a frequency ratio (FR) of the vibration frequency to the natural frequency at or above a predetermined value.

12. The system of claim 11, further comprising a first controller configured to provide signals to the actuators.

13. The system of claim 12, further comprising one or more sensors configured to provide vibration information of the working platform.

14. The system of claim 12, the first controller configured to:

receive signals from the one or more sensors configured to measure vibration frequency of the working platform;

determine the cable tension based on a previous calculated value of the natural frequency of the working platform and the FR;

provide signals for the two or more actuators to adjust the corresponding cables;

calculate a new natural frequency of the working platform; and

compare the FR to a predetermined value.

15. The system of claim 12, further comprising a second controller coupled to and adapted to control the two or more actuators, whereby two or more control signals are calculated for the two or more actuators based on a target position from a current position of the working platform according to one of (i) an open-loop configuration, (ii) a first closed-loop configuration utilizing velocity of the working platform as a feedback signal, or (iii) a second closed-loop configuration utilizing velocity of the working platform as a first feedback signal and the position information of the working platform as a second feedback signal.

16. The drive system of claim 15, wherein each of (i) the open-loop, (ii) the first closed loop, and (iii) the second closed loop configurations initially calculates the target pose vector of the working platform.

17. The drive system of claim 16, wherein the target pose vector is calculated based on

l₁=[l₁₁ l₁₂ . . . l_ln]^T,l_s=[l_s1 l_s2 . . . l_sn]^T, and l_e=[l_e1 l_e2 . . . l_en]^T whereby

l_li represents length of each of the two or more cables and which includes l_si which represents an inelastic portion and l_ei which represents an elastic portion,

l_s*=l₁*−

l_e where * denotes the target representation of the working platform, and is calculated based on

M{umlaut over (x)}+C{dot over (x)}+G=−

J^Tτ

where M represents inertia matrix,

C represents Coriolis matrix,

G represents gravity matrix,

J represents Jacobian matrix, and

τ

represents tension in the two or more cables, which yields n−

1 equations for n cable tension unknowns which can be solved for a tension solution, and where tension and the change in l_e are related based on

τ

=EA·

diag<sup>−

1</sup>(l_e)Δ

l_e, where

E represents Young'"'"'s modulus of elasticity of the elastic portion and A represents cross sectional area of each of the two or more cables, and

Δ

l_e represents extended length of each of the two or more cables and is defined by l₁−

l_s−

l_e and

18. The drive system of claim 17, wherein the n−

1 equations and n unknowns can be solved for each tension of the two or more cables based on minimum norm least-squares.

19. The drive system of claim 18, wherein the Jacobian matrix is defined by

20. The drive system of claim 15, further comprising one or more velocity sensors configured to provide velocity information of the working platform and one or more position sensors configured to provide position information of the working platform.