| Motion Control

Imitative Robotic Control: The Puppet Master

Automated systems can have a hard time completing complex tasks in a timely manner. When controlling a robot outside autonomous mode, a good control device needs to give the user full control of the system while enabling the mission to be completed in a quick, accurate, and efficient manner.

© Copyright 2015 by RE2, Inc.
As ground robotics moves towards autonomous and semi-autonomous operations, the need to have full control over manipulators is still required for complex situations, or when a user feels the need to take control of the system. Repetitive tasks tend to be the tasks in which humans begin to feel fatigued and make mistakes. Automation is often great in these situations. Complex tasks keep a human alert and thinking as long as the task can be performed in a short amount of time. Automated systems tend to have a harder time completing these complex tasks accurately and in a timely manner. Research has shown that when con - trolling a robot outside autonomous mode, a good control device needs to give the user full control of the system while enabling the mission to be completed in a quick, accurate, and efficient manner. Additional research shows that limitations in a control device can often reduce the usefulness of the robot.

In recent years, manipulators have become more capable and more dexterous through additional degrees of freedom. As a result, new control techniques and new control devices are required. Techniques such as “flying the end effector” require little cognitive load when working in environments with a minimal amount of obstacles, but users do not have control of all the joints and links with this control method. This can potentially result in unwanted configurations of the robot or collisions with obstacles. Current methods for having full control over all of the joints often require moving one or two joints at a time through the use of knobs or buttons, resulting in an overall system that is hard to control, very slow, and is tedious for the operator.

A wide range of existing control devices was studied with the goal of determining which were the most intuitive to use, and resulted in the fastest and highest success rate for common tasks. This research also looked into combining devices to utilize the positive aspects of the devices while canceling out the negative aspects. The project looked at existing products and techniques to determine their strengths and weaknesses in terms of ease of control and their extensibility to additional degrees of freedom, among other factors. This research identified several approaches to manipulation control of high-degree-of-freedom arms. In-depth testing and analysis was performed of the most promising devices with a wide range of users. These prototypes and concepts led to further research and development of the most promising solution — a puppet controller —through a contract with the U.S. Navy. This new control device, called the Imitative Controller (IC), allows the user to move a scaled model, sometimes referred to as a puppet, of the robot’s manipulators. This controller has been shown to effectively control a highly dexterous two-arm system, consisting of two 7-degrees-of-freedom arms and a 2-degrees-of-freedom torso (16 total degrees-of-freedom), called the Highly Dexterous Manipulation System (HDMS).


Figure 1. The Imitative Controller (top) in a configuration set to be a scaled-down match of the joints and links of the HDMS robot (bottom).

A puppet control device is often comprised of joints and links that are to the scale of the robot that the device is controlling. The joints have encoders in them to determine the position and orientation of the device, which is then translated to movement and position commands for the robot. In the case of IC (Figure 1 top), the user holds onto a handle and moves their hand around, which moves all of the joints and links between the handle and the base of the device. Given that the puppet device is a model of the robot, the robot will attempt to match the position and orientation in a master/slave relationship. This point of interaction between the human and the control device is similar to that used for flying the end effector.

In this respect, the user is using the device in a similar manner, but with a puppet device, they get a physical confirmation that the overall state of the robot will consist of a set of specific positions and orientations. Flying the end effector relies on mathematical formulas that can produce multiple solutions to the same desired position and orientation, resulting in an unknown final state of the robot, even when the position and orientation of the end effector is known.


Figure 2. A grip with a handle that is at an angle (left) offers better ergonomics to the user when compared to straight handles (right).

Recent research has centered around handle types, handle locations, and the overall size, or scaling factor, of puppet systems in order to optimize the user’s experience and ensure the most accurate and intuitive control of the robot. Handle types refer to the style of grip that is intended as the connection point between the user and the control device. It was found that the best handles are those designed to fit in the user’s hand in such a manner that it is at an angle to the piece of the control device being controlled, such as the grip on the lefthand side of Figure 2.