Robot arm with human motion dynamics

Article of 31 March 2017 

BionicCobot

For many jobs carried out in production, people wish they had a third hand. When doing soldering work, for example, the soldering iron must be held in one hand and the solder wire in the other, leaving no hand free for the workpiece. The BionicCobot developed by Festo can help precisely with such assistance activities and relieve the employee by acting as a “third arm” or “third hand”. It can grip, hold and rotate the workpiece – whatever is required for the relevant application.

The Festo BionicCobot is a seven-axis lightweight robot, which is moved solely using pneumatic semi-rotary drives. Its movements are based on the human arm. Like its biological role model, it makes use of the natural working mechanism of the biceps and triceps muscles – and does so not only in one, but in all seven joints. Thanks to the drive concept and the sophisticated control technology, the robot arm can be directed like the human arm and move quickly and powerfully, but also sensitively and flexibly depending on the situation.

Flexibility as a major advantage of the pneumatic robot

One important feature of pneumatics – and hence of the pneumatic robot arm too – is its flexibility inherent to the system. It comes about because the air in the drive chambers can be compressed.
On the BionicCobot, this leads to a critical benefit over robots that are moved with geared motors, for example. In the event of a collision with an obstacle, the afore-mentioned ability of the air to compress immediately takes effect. In accordance with this, the robot behaves intrinsically flexibly and contributes to a certain degree of safety. The BionicCobot’s position controller will naturally make the actual flexible and vibratory pneumatic system more rigid. As the controller only responds some time after a collision, however, the potential danger in the event of a collision is reduced.

As each drive chamber of the seven axes is operated separately with a valve on the BionicCobot, the pressure level of each axis can be individually adjusted. The torques of each separate joint can thus be controlled depending on the application. In this way, the robot can also fulfil tasks where it has to be powerful. For example, if it is supposed to hold an object in a certain position or apply a counteracting force.

In contrast to a powerful movement, however, the torques can also be exactly adjusted so that the robot can hold “itself” and the workpiece. The robot’s gravitational force differs depending on the position of the arm. This is mathematically calculated and compensated for accordingly. The gripped load can therefore be directed almost weightlessly by the operator.

Typical application for the BionicCobot: it can hold the workpiece during soldering
Typical application for the BionicCobot: it can hold the workpiece during soldering

Complex regulation and control technology

Pneumatic drives are installed in the BionciCobot's joints, which move the robot. Sensors are also fitted in the axis modules for measuring the joint angles and the pressure for recording the chamber pressures. Although the necessary regulation and control technology is complex, it enables a so-called path follower control, which is not possible with standard pneumatics: in robotics, a required movement is usually planned in so-called gripper coordinates and converted into joint angles. The individual movements of the seven joints on the BionicCobot are thus coordinated so that the whole robot arm performs the required movement. In this way, the BionicCobot can help with many assistance activities - as a third hand.