Hydrabot
The Modular Electro-Hydraulic Robot Arm
By:
4B Honors Mechatronics Engineering, Co-op,
University of Waterloo
Under the supervision of:
Deputy Chair of the Department of
Mechanical & Mechatronics Engineering, University of Waterloo
Jump to: Project Description, Results, Sponsors, Acknowledgements, Documents, Contact Information, Relevant Links
Project Description
A
robot arm, as shown in Figure 1 below, is a series of links whereby each link
is capable of moving in relation to other links. Actuators are the devices
responsible for moving the links, and these are powered either electrically,
hydraulically, pneumatically. An end-effector, such as a camera or gripper, is
mounted onto the end of the arm, and this is the device responsible for
interacting with the environment. Sensors are used to provide information on
the position and movement of the robot arm. Robot arms may be thought of as
being similar to human arms: the links being the bones, the actuators being the
muscles, the end-effector being the hand, and the sensors being the
proprioceptive feedback. Robot arms have found numerous applications, such as
in industrial automation and in places where it is too dangerous (e.g. in a
radioactive environment) or impractical (e.g. in space) to have a human arm.
Figure 1 An industrial robot arm.
Image obtained from Wikipedia.
Modular
robot arms are kinematic chains consisting of identical modules which can be
easily assembled or disassembled. This gives the user control of the number of
degrees of freedom (or the number of joints) in the arm by simply adding or
subtracting modules. Most modular robot arms are also reconfigurable, meaning
that the user also has flexibility in the orientation of each module. This
gives the user the ability to change the shape of the arm and the workspace (or
reach) of the end-effector. A modular robot arm that is not reconfigurable
would be restricted to movement in a single plane, which would make it
unsuitable for most applications of modular robot arms. Modular, reconfigurable
robots have found applications wherever a robot arm with many degrees of freedom
is needed, such as when the robot arm is expected to reach around an object or
manoeuvre itself into a confined space such as a pipe, duct, or small
compartment. Currently, there are three suppliers for such robots: Amtec,
Schunk, and OC Robotics. These robots are shown in Figure 2 below. Amtec offers
its “PowerCube” line of modules for modular and reconfigurable robots. These
modules consist of two cubes, one cube being a servo motor while the other
being a gearbox. Schunk also offers modular and reconfigurable robots. In
Schunk’s robots, the modules are not the same size (e.g. the lower modules are
larger than the upper ones). OC Robotics is the only commercial supplier of
snake-arm robots, which are capable of continuous curvature. Their robots work
by attaching three cables to the top of each module and adjusting the tension
in the cables in order to position the modules.
Figure 2 Modular, reconfigurable robots
offered by Amtec (top left) and Schunk (top right). Snake-arm robot offered by
OC Robotics (bottom).
As shown in Figure 2 above, all commercially-available modular robots use electrical actuators. This project attempts to increase the payload and to increase the number of modules which can be supported in a modular and reconfigurable robot arm by using hydraulic actuators, since hydraulic actuators have higher power-to-weight ratios than electrical actuators. A prototype consisting of two modules will be fabricated. The design uses two Parker hydraulic cylinders that act on a torque arm. Rotation of the torque arm causes rotation of the next module (or link) in the robot arm. Since both cylinders are connected to the torque arm, their motion is dependent on each other and only one valve is needed to control both cylinders. A Parker proportional valve is chosen for this task. Position feedback of the modules is obtained by rotary potentiometers. Figure 3 below shows the 3D model of the design. A more detailed description of the design can be found in the design report (.pdf, 2MB).
Figure 3 3D model of design shown with
the cylindrical housing (left), 3D model without the cylindrical housing
(middle), and photograph of the actual module (right). In the 3D model, the
cylinders are colored yellow and the valve blue.
Results
On March
18, the robot was completely assembled and connected to a hydraulic powerpack.
Since then, the robot has been running very well, producing fast, smooth, and
accurate movements. Figure 4 below shows the robot’s response to a 45° step
command. More detailed information regarding the fabrication, testing, and
results, as well as the engineering drawings of the prototype can be found in
the final report (.pdf, 2.8 MB).
Figure
4 3D model of design shown with the cylindrical
housing (left), and without the cylindrical housing (right). The cylinders are
colored yellow and the valve blue.
The robot
performed very well at the symposium on March 23, 2009. It made a very
impressive exhibit as it ran nonstop through the entire symposium, completing
nearly 2,000 movements. A video of the robot is shown below:
Sponsors
This project would not be possible without generous donations from Parker Hannifin Corporation (who provided the valves and the cylinders), MP Filtri (who provided the filter necessary for the valves), and from the Department of Mechanical & Mechatronics Engineering (who provided space, the powerpack, and covered the remaining costs).
Acknowledgements
I would like to thank Professor Jan P. Huissoon for his valuable advice regarding the overall design, John Potzold and Kwai Chan for their valuable advice regarding the fabrication, Robert Wagner for manufacturing the base (manifold) plates and the top plate, Rick Churilla for his help in getting me sponsorship from Parker, Rob Chin for his help in getting me sponsorship from MP Filtri, Andy Barbor for his advice on the electronics, Jim Johnson and Terry Seip for helping me with the plumbing, and so many of my classmates who have given me valuable technical and non-technical advice.
Documents
1. Final
Report (.pdf, 2.8MB) – Completed on April 6, 2009
2. Poster (.pdf,
0.5 MB) – Displayed at the symposium on March 23, 2009
3. Design Report (.pdf, 2MB) – Completed on Dec. 1, 2008
4. Final Design Presentation (.ppt, 9MB) – Presented Nov. 17, 2008
5. Preliminary
Design Presentation (.ppt, 1.4MB) – Presented Sept. 15, 2008
Contact Information
Please feel free to email me at abed.alnaif@gmail.com.
Relevant
Links
1. Parker
Hannifin Corporation – designer and manufacturer of motion control products
2. MP Filtri – designer and manufacturer of hydraulic filters, as well as power transmission components and accessories for hydraulic power units
3. Department
of Mechanical & Mechatronics Engineering at the University of Waterloo
4. Other cool
projects by the Mechatronics 2009 class
5. Video of Schunk modular robot arm
6. Videos of OC Robotics snake-arm robot
7. Good explanation of current fluid power technologies and fluid power design here and here
Last Updated: April 8, 2009