Sensor boosts robot versatility

Sensor boosts robot versatility

Keywords Manufacturing,Robots, Sensors

When even minor changes need to be made to a manufacturing process, people need to teach the new process to the robot by guiding it manually through each motion and orientation in the operation. Besides being time-consuming and expensive, this process can also be inaccurate. A new sensor developed by the Lawrence Livermore National Laboratory in Livermore, promises to eliminate much of this education by making industrial robots more adaptable to new situations.

Four assemblies comprise the six-degree-of-freedom (DOF) sensor: a laser illuminator, beamsplitting and directional optics, lateral-effect photodiodes, and signal-processing electronics. Two small mirrors guide the 1 millimetre laser beam through two negative lenses that diverge the beam at about 0.3 radians. This high divergence creates a 2 centimetre laser spot approximately 3.5 centimetres from the face of the sensor. Beam divergence, depth of field, and spot size can be changed by choosing different negative lenses.

Two reflective points, a 4 millimetre dot, and a 1 by 1 millimetre bar are mounted on non-reflective tape and applied to the part being worked on. The laser light reflects off the references and back into the sensor. Since the beam is diverging, the reflections are magnified in the area when the light returns to the sensor,allowing most of the light to go around the negative lenses and through a large,collimating lens instead.

Inside the sensor are three photodiodes, each of which has a different sensitivity to the relative position of the sensor and the reflectors. As a result, they can determine all three positions and orientations of the sensor relative to the part. The signals from the photodiodes are processed by electronics remotely located from the sensor head.

In an industrial environment, parts could be coated with these reflectors. When the parts are delivered to the robot, they do not have to be accurately positioned, and the robot does not need to be trained. Instead, the information from the sensor allows the robot to align to the part.

Potential applications are even more diverse. For example, there are ways to encode task information into reflectors, so the robot could also ascertain what task to perform on a particular part. In addition, the sensor could be used for inspecting and tracking objects like airplanes and cars because it is range-independent when functioning as a four-DOF sensor. Another application currently under development is a three-dimensional computer mouse. Livermore is currently working with various companies to work out licensing agreements.

For more information see Sensor Review, Vol. 18 No. 2, 1998, pp. 73-74, Viewpoint ­ "A new six degrees of freedom position sensor greatly improves flexible manufacturing­ but will manufacturers adapt?"