Robots are often part of cells where high precision tasks may be performed, such as assembly, welding, pick and place that are often complex and repetitive. Being an integral part of the Industry 4.0 new paradigm, collaborative robots have started to be integrated in smart manufacturing eco-systems. These robots can work together with human operators in close proximity and can support operators in performing a series of tasks, while reducing the workload of the operator.
Typically, collaborative robotic arms are fixed in a specific location, for instance, mounted on a table. They can handle objects within their reach and their workspace is limited by the robot configuration and characteristics. Therefore, collaborative robots mounted on mobile platforms, also called collaborative mobile robots, can provide additional capabilities, such as transferring parts from one place to another, or more degrees of freedom in terms of the overall movement capabilities. In recent years, both industrial and research communities are investigating various areas and applications where collaborative manipulators can be effectively used in order to solve real-world problems.
At UCD-Laboratory for Advanced Manufacturing Simulation and Robotics (UCD-LAMS), one such potential area was investigated, where collaborative mobile manipulators can support human operators in a shopfloor with the transportation of long objects from one place to another. Practically, there are various levels of complexity involved in creating a task that enables the co-manipulation of objects. Some of the main challenges are :
- Complexity of programming.
- Understanding the architecture of the collaborative mobile manipulator.
- Nature of the environment – obstacles, relocation of objects within the shopfloor.
At UCD-LAMS a set of novel control algorithms were developed for allowing the manipulation of long parts by both mobile robot platforms and operators.
An aluminium profile is required to be transported from one place to another with the help of a collaborative mobile manipulator. The collaborative mobile manipulator grabs one end of the aluminium profile, and the operator holds the other end. The operator guides the robot in order to move the aluminium profile to an another place in a shop floor. The collaborative robotic arm has inbuilt collision detectors (Force/Torque sensors) that can detect a collision and therefore provide a signal to the robot controller to stop when it comes in contact with humans or objects. Also, the collaborative arm features impedance control that enables the operator to move the arm around freely. In the proposed control strategy that was developed, the force sensor feedback coupled with the cartesian impedance control were used to create a haptic feedback response. The haptic feedback is translated into a format that is understandable by the robot controller. This response is used to navigate the robot from one place to another while carrying a long part with ease.
Figure 1. The Aluminium profile held by the operator on one end and the robot on the other end.
Figure 2. Co-manipulation of long parts from one place to another. The operator guides the robot after the aluminium profile is picked up, where the robot holds on to one end and the operator to the other end.
In summary, the advantages of using a collaborative mobile manipulator include the ability:
- To perform a safe, coordinated transfer of long parts from one place to another
- To provide a cost-effective and ergonomically sound way to use mobile robotic platforms for complementary tasks in typical shop-floor environments.
- To eliminate the need for using special safety equipment, devices, fixtures and sensors while introducing robot-based automation capabilities in the shop floor.
 A. K. Ramasubramanian and N. Papakostas, “Operator - mobile robot collaboration for synchronized part movement,” Procedia CIRP, 2021.