Position-based impedance control of a hydraulic rock breaker boom
Hulttinen, Lionel (2017)
2017
Automaatiotekniikka
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2017-12-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201711232237
https://urn.fi/URN:NBN:fi:tty-201711232237
Tiivistelmä
This thesis considers the automatization of a rock breaker boom equipped with a hydraulic hammer. The studied use case of an automatized breaker boom consists of trajectory generation from a standby position to preprogrammed locations on a steel grid. The operator shall be able to choose a specific location of the grid from a user interface and the boom shall automatically move above the chosen location, do an approach movement towards the grid and switch the hydraulic hammer on when contact with an external object is detected. During this sequence the angle of the rock hammer should be constantly maintained at vertical orientation relative to the grid.
The developed solution for contact detection is based on impedance control, which is a form of indirect force control built on top of an underlying operational-space tool centre control scheme. To implement impedance control for hydraulic manipulators, pressure sensors and knowledge of boom kinematics and dynamics are necessary. In its simplest form, modeled configuration-dependent gravitational forces affecting the hydraulic cylinders are subtracted from pressure readings and mapped into forces affecting in Cartesian space to yield a rough estimate of contact forces affecting on the manipulator. The estimated contact forces are then filtered into a position modification that indirectly regulates the force affecting on the tool tip of the manipulator. The force tracking performance is dependent on the underlying position controller, which is why the control scheme is referred to as position-based impedance control.
In this thesis, an impedance controller was developed for a four degrees-of-freedom hydraulic manipulator and it was verified using a simulation model of the manipulator. The sequence was implemented on the actual breaker plant and a simple position controller was tuned, but the original objective of identifying dynamic parameters and testing of the impedance controller for contact detection as a part of the automatic sequence was not met.
The developed solution for contact detection is based on impedance control, which is a form of indirect force control built on top of an underlying operational-space tool centre control scheme. To implement impedance control for hydraulic manipulators, pressure sensors and knowledge of boom kinematics and dynamics are necessary. In its simplest form, modeled configuration-dependent gravitational forces affecting the hydraulic cylinders are subtracted from pressure readings and mapped into forces affecting in Cartesian space to yield a rough estimate of contact forces affecting on the manipulator. The estimated contact forces are then filtered into a position modification that indirectly regulates the force affecting on the tool tip of the manipulator. The force tracking performance is dependent on the underlying position controller, which is why the control scheme is referred to as position-based impedance control.
In this thesis, an impedance controller was developed for a four degrees-of-freedom hydraulic manipulator and it was verified using a simulation model of the manipulator. The sequence was implemented on the actual breaker plant and a simple position controller was tuned, but the original objective of identifying dynamic parameters and testing of the impedance controller for contact detection as a part of the automatic sequence was not met.