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Mitsubishi shows ‘flexible location robots’ at Automatica Exhibition in Munich

14 June 2010

A newly-developed process combines advanced sensor technology and real-time control so that flexible location robots can quickly react to changes in their environment and adapt their trajectory to suit — even after the arm has already started its motion. The surprising thing is, there’s no machine vision involved. It's all done with sensors.

Mitsubishi’s demo at Automatica: passing the die, without machine vision.
Mitsubishi’s demo at Automatica: passing the die, without machine vision.

Mitsubishi Electric claims the sensor guided real-time control does not require any elaborate programming. The company was showing its robots and the system developed by Robotics Technology Leaders (RTL) at the Automatica 2010 trade fair in Munich.

Virtual Reality Floor

RTL says it is using a new technology called the VRFloor (Virtual Reality Floor) positioning system and has had a successful implementation in robot assisted television cameras at the News studio of Zweiten Deutschen Fernsehen (ZDF.)

The system includes passive markers with a constant identity, sensors for registering the marking points and a control computer for analysing the sensor information. The various types of markers are fitted around three millimetres below the floor surface.

An air cushion ensures the mobility of the robot, which can be moved within the work cell, and transferred to other production stations. The sensors are fixed on the base of the robot and to other moving objects in the working area such as a work piece carrier.

The advantage of this set-up is that it is no longer necessary to precisely align and position work pieces fed into the work cell. The positioning system works without contact and without wear.

Sensor guided real-time control: taking its first European bow, Mitsubishi’s mobile six axis articulated-arm robot RV-2SDB.
Sensor guided real-time control: taking its first European bow, Mitsubishi’s mobile six axis articulated-arm robot RV-2SDB.

Real-time controller

"To be able to make robots and manufacturing stations so flexible, a real-time controller is indispensable," said Dr Stefan Riesner, Managing Director of Robotics Technology Leaders GmbH in Munich, a small systems integration company that works with Mitsubishi.

The fast interchange of data between sensor and controller puts the robot in a position to react directly to changes in the work area and to determine its trajectory during movement on the basis of current sensor values.

A computer calculates the movement information from the signals and transfers the position data in quick succession to the robot controller, typically within one to 10 milliseconds. For a 15 centimetre curved motion of the robot arm — which takes place in a period of three seconds, for example — 1,500 positions must be transferred to the robot controller with a cycle time for the robot of two milliseconds.

Mitsubishi’s robots on display

The youngest member of Mitsubishi’s robot family, the RV-2SDB (photo), made its European debut and was used to demonstrate the real-time control capability. It is a six axis articulated-arm robot type with a two kilogram load capacity and a 504 mm reach, which is particularly manoeuvrable because of its construction.

The robot arm has a slewing range of plus/minus 240 degrees and can thus turn to both sides beyond its radius of action of 360 degrees. At a speed of up to 4,400 mm per second the robot, which is braked on all axes, can achieve a repeat accuracy of two hundredths of a millimetre.

Fast data exchange: With a standard cycle for the robot of two milliseconds, the robot controller must process 1500 positions in three seconds for a movement of 15 centimetres.
Fast data exchange: With a standard cycle for the robot of two milliseconds, the robot controller must process 1500 positions in three seconds for a movement of 15 centimetres.

Lessens the need for programming

“The reliable self-positioning of the mobile robot dispenses with the need for the often highly time-consuming and expensive programming, which frequently makes it unprofitable to use stationary industrial robots, particularly for small batch sizes, high numbers of variants and quick product changes,” said Mr. Riesner.

Commissioning and operating the system requires no programming knowledge, he says. The operator configures the planned working processes for the robot once only, using the teach-in process. From this the control software calculates all the required values for the programme sequence in operation and using sensor data automatically corrects deviations from the original position of the robot and the objects.

The mobility of the robot requires an adaptable safety system consisting of a three-dimensional model of the work cell. The model makes it possible to check if the robot is moving on a collision-free trajectory and prevents impacts with other objects in the environment.

In the Mitsubishi Electric demonstration at the Automatica Exhibition, a robot moving on an air cushion picked up a die thrown by a second robot. It would then pass it to a fixed location partner. The random position of the die was determined without a camera to an accuracy of less than 25 hundredths of a millimetre.


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