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UBC Theses and Dissertations
Identification of frictional effects and structural dynamics for improved control of hydraulic manipulators Bilandi, Shahram Tafazoli
Abstract
Frictional terms and structural dynamics play an important role in achieving high quality performance of hydraulic manipulators. This thesis is mainly concerned with the identification of these effects and compensation thereof through control, for two different industrial applications. The first application pertains to a Cartesian electrohydraulic manipulator of a prototype fish processing machine which has been developed in the Industrial Automation Laboratory. Both modelbased and observer-based approaches to friction estimation are investigated for this basic system. In the first approach, a friction model is used that is linear in parameters, and the friction is assumed to be a fixed function of velocity. The model parameters and the object mass are determined by applying the least squares estimation procedure to experimental data. A combination of Coulomb, viscous, and Stribeck components are observed in the identified friction model. In the second approach, a modified version of an available nonlinear observer is used for real-time estimation of the friction parameter. Convergence rate of the observer is analyzed and an approximate algorithm is developed for choosing its gains. Next, a novel technique is developed for friction-compensated tracking control of the manipulator. The technique incorporates the estimated frictional force in an acceleration feedback control law. Specifically, the model-based approach to friction estimation results in a fixed friction compensation algorithm and the observer-based approach to friction estimation results in an adaptive friction compensation algorithm. Experimental investigations show that the technique that is presented in this thesis considerably improves tracking performance of the manipulator. The second application is a mini excavator system which is a typical example of the humanoperated mobile hydraulic machines. A new technique is presented in this thesis for indirect measurement of the joint torques of the backhoe links using load pin force sensors. Also, to be able to control the link motions electronically, the original pilot stage is modified by using on/off solenoid valves that are operated with DPWM (Differential-Pulse-Width-Modulation) current signals. Modeling and identification of the modified pilot stage is studied in the thesis in detail. According to the experimental results, the designed switching pilot system has a reliable performance that is linear. After the instrumentation phase, experiments are carried out with the mini excavator to determine the mass and inertia-related parameters of the links. To estimate the six mass-related (gravitational) parameters, sensor outputs are recorded in various static poses of the manipulator. The least squares estimation procedure is then applied to the decoupled form of the torque equations. The validation tests which we have carried out verify that the identified parameters can be used to estimate the static joint torques, with a good accuracy. An efficient algorithm is then developed for real-time estimation of the bucket load under static conditions. Experimental results show that the bucket load can be estimated at an accuracy level of 5%. To study the structural dynamics of the system, the Euler-Lagrange equations are derived for the manipulator. The structural (dynamic) parameters are defined using these equations. It is shown in this thesis that the six gravitational parameters are a subset of the nine dynamic parameters. Joint friction coefficients are then added to the parameter set. Finally, the combination of the dynamic parameters and friction coefficients are estimated from the identification data that is obtained by simultaneous movement of the links. The results are consistent with those of the static experiments. In this research, it is found that the friction inside the actuator seals is quite significant. It follows that the joint torques can be measured more accurately by using load pins instead of pressure sensors.
Item Metadata
Title |
Identification of frictional effects and structural dynamics for improved control of hydraulic manipulators
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1997
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Description |
Frictional terms and structural dynamics play an important role in achieving high quality
performance of hydraulic manipulators. This thesis is mainly concerned with the identification
of these effects and compensation thereof through control, for two different industrial applications.
The first application pertains to a Cartesian electrohydraulic manipulator of a prototype fish
processing machine which has been developed in the Industrial Automation Laboratory. Both modelbased
and observer-based approaches to friction estimation are investigated for this basic system. In
the first approach, a friction model is used that is linear in parameters, and the friction is assumed to
be a fixed function of velocity. The model parameters and the object mass are determined by applying
the least squares estimation procedure to experimental data. A combination of Coulomb, viscous,
and Stribeck components are observed in the identified friction model. In the second approach, a
modified version of an available nonlinear observer is used for real-time estimation of the friction
parameter. Convergence rate of the observer is analyzed and an approximate algorithm is developed
for choosing its gains. Next, a novel technique is developed for friction-compensated tracking control
of the manipulator. The technique incorporates the estimated frictional force in an acceleration
feedback control law. Specifically, the model-based approach to friction estimation results in a fixed
friction compensation algorithm and the observer-based approach to friction estimation results in an
adaptive friction compensation algorithm. Experimental investigations show that the technique that
is presented in this thesis considerably improves tracking performance of the manipulator.
The second application is a mini excavator system which is a typical example of the humanoperated
mobile hydraulic machines. A new technique is presented in this thesis for indirect
measurement of the joint torques of the backhoe links using load pin force sensors. Also, to be
able to control the link motions electronically, the original pilot stage is modified by using on/off
solenoid valves that are operated with DPWM (Differential-Pulse-Width-Modulation) current signals.
Modeling and identification of the modified pilot stage is studied in the thesis in detail. According to
the experimental results, the designed switching pilot system has a reliable performance that is linear.
After the instrumentation phase, experiments are carried out with the mini excavator to determine
the mass and inertia-related parameters of the links. To estimate the six mass-related (gravitational) parameters, sensor outputs are recorded in various static poses of the manipulator. The least squares
estimation procedure is then applied to the decoupled form of the torque equations. The validation
tests which we have carried out verify that the identified parameters can be used to estimate the
static joint torques, with a good accuracy. An efficient algorithm is then developed for real-time
estimation of the bucket load under static conditions. Experimental results show that the bucket load
can be estimated at an accuracy level of 5%. To study the structural dynamics of the system, the
Euler-Lagrange equations are derived for the manipulator. The structural (dynamic) parameters are
defined using these equations. It is shown in this thesis that the six gravitational parameters are a
subset of the nine dynamic parameters. Joint friction coefficients are then added to the parameter set.
Finally, the combination of the dynamic parameters and friction coefficients are estimated from the
identification data that is obtained by simultaneous movement of the links. The results are consistent
with those of the static experiments. In this research, it is found that the friction inside the actuator
seals is quite significant. It follows that the joint torques can be measured more accurately by using
load pins instead of pressure sensors.
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Extent |
7496132 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-04-03
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0065122
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1997-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.