Electricity: motive power systems – Positional servo systems
Reexamination Certificate
1993-12-20
2003-01-14
Sircus, Brian (Department: 2839)
Electricity: motive power systems
Positional servo systems
C318S565000, C318S568120, C318S568250, C318S628000, C318S649000, C014S078000, C015S300100, C015S321000, C015S340100, C015S346000, C901S034000, C901S043000, C901S047000
Reexamination Certificate
active
06507163
ABSTRACT:
BACKGROUND OF THE INVENTION
Bridges, especially bridges over highways, require vigilant maintenance to protect their strength.
Highway maintenance trucks have been developed in which the entire bed of a truck is raised on scissor movements so that workers can access bridge beams and superstructures directly for cleaning, chipping and sand blasting, and subsequently for painting.
The bridge maintenance work is difficult, dirty, environmentally exposed and highly skilled work and is therefore accomplished at great expense. The work is especially dangerous because the work requires being physically close to speeding traffic, closing busy highway lanes and erecting appropriate warnings and barriers. Moreover, the job is extremely dangerous because contact of the support truck by fast moving traffic might result in jarring of the raised truck bed and ejecting of a person from the raised bed onto the roadway surface below.
Because of the natures of the coatings and the coating removing processes which are employed, it is necessary for workmen to wear heavy protective gear. The heavy protective gear makes working conditions extremely difficult and results in prolonged efforts required for maintenance of individual bridges.
A need exists for a system which avoids the expenses, dangers and discomforts of the prior art systems.
One process especially suited to robotics applications is bridge painting. Poor worker safety and the inefficient labor intensive procedures used in bridge painting presents an opportunity to apply robotics technology to that process in a cost effective way.
This invention improves safety and at the same time reduces the cost of bridge painting. Other designs have tried to improve productivity by providing the workers easier access to work spaces or through more efficient hand tools. However, no previous attempts to improve the process have been successful.
Superstructures of highway overpasses are the areas targeted by this invention. Those types of bridges comprise the majority of bridge structures in this country. Although those structures can vary in dimension, they maintain the same basic beam stringer type structural characteristics consisting of consecutive I-beams spanning supports. That provides a certain degree of conformity, enabling an automated containment process.
The invention includes the tools necessary to accomplish all tasks associated with stripping and repainting bridge surfaces. Viewing the work space through remote cameras located atop the robot arms and at either end of the platform, the worker controls the unit from the ground using a control panel and an interactive master-slave manipulator. That eliminates the need for workmen to ascend to the work space, thus preventing exposure to the harmful particles generated during this process and to falls due to accidents.
The system has two robot arms shielded in latex sleeves and mounted atop a platform. The platform is positioned beneath the targeted structure using a mobile hoisting system modified from a man lift. A control unit containing both the master manipulator and a control panel is affixed to the man lift, enabling the entire system to maneuver independently. Once in position, containment barriers are deployed to contain the work space, and work commences.
The entire system can be carried aboard a truck. The man lift is capable of either operating from atop the truck bed or maneuvering off the bed to locations inaccessible to the truck. Unlike conventional methods, this system disrupts only one lane of traffic when in operation.
To accomplish the goal of automating this process, a new control system is created. An existing platform system is modified to suit the application. That platform is raised into position, carrying the robot arms and their supporting gear. A vision system is employed to enable the user to view the work space adequately from a remote location. A gripper adds dexterity and flexibility to the arms. A paint removal and collection system and a new automated containment system prevents lead from escaping into the environment. A single control panel integrates the controls of each of the system's utilities.
The new control approach allows the user to feel the forces exerted by the remote arm. A master manipulator is included. In one embodiment, a controller controls three degrees of freedom. The control system may have six degrees of freedom plus a gripper.
The invention provides a integration of various systems such as a paint application system, a sand blasting system, a vision system, a gripper, a surface cleaning system, and a canvas and inflatable containment system.
A platform carries the system up to the bridge I-beams and facilitates use of the various systems.
A commercially available robot arm and controller is employed. Modifying an existing arm facilitates needs.
Preferred robot arms have eight degrees of freedom. They consist of a three-joint wrist, an elbow joint and a two-joint shoulder. That part of the arm consists of six joints and is similar to a Puma manipulator and a human arm. The human arm has a three-joint shoulder instead. Such similarities are important, since they provide good intuition when controlled by a human arm via a master manipulator. The arm is mounted on a two axis table with one horizontal axis and one vertical axis. The two linear motion degrees allow the tool to move efficiently along two linear directions and ease control of the master. The overall eight joints provide good dexterity for the robot, helping it avoid obstructions.
A master-slave control system is capable of interactive control. This configuration allows an operator to control the robot arm by simply inserting his arm into a sleeve. Then whatever movement the operator executes with his arm is duplicated by the remote robot arm. However, unlike conventional master-slave manipulators, the invention provides the user with the ability to feel the actions of the remote arm in real time through a controller force feedback system.
In a new force control approach, the axes on the master manipulator are equipped with encoder motors. When the user begins to move his arm, the master manipulator sends pulses from the encoders to the controller. The pulses are used as desired positions to implement a proportional derivative control algorithm in the controller. The controller then generates a current for the motors on the slave robot based on that algorithm to bring the slave robot arm back into synchronous motion with the master controller.
A fraction of the current generated for each of the slave robot arms axes is diverted to the corresponding joint motors of the master manipulator by way of a current divider. The resultant motor torque opposes the motion of the master manipulator. That opposition is felt by the operator. Since current is proportional to torque, the operator feels a proportional torque representative of the forces applied on the remote arm.
The result of this control capability is that it gives the operator the ability to apply precise forces to objects within the arm's environment. That is accomplished by using a human in the control loop. The implemented position and force control is then greatly simplified by the elimination of complex position and force control algorithms, force sensors, and interfacing microprocessors common to other force feedback systems.
Once the arm is in contact with an object, the user can increase the forces applied by continuing to move the master in the object's direction. That results in an increase in the difference between desired and actual positions, causing the controller to increase current to both the master and slave motors.
The current divider also simplifies the system by allowing use of an off-the-shelf controller with only minor modifications and no additional axes capabilities. All of these simplifications help reduce development time and cost.
This system prevents the user from inadvertently damaging the robot arm by limiting the motor currents. That is accomplished by adjusting the opposing cur
Creighton Wray James
Narasimhan Meera P.
Sircus Brian
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