Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1997-09-19
2000-02-08
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
G01S 1793
Patent
active
060230649
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an object sensing system, particularly, but not exclusively, an object sensing system for use in a collision avoidance system of an automated manipulator.
There are a number of known range sensing systems used in a variety of applications. One such application is in collision avoidance systems of automated manipulators such as robot arms. Collision avoidance systems are useful in teleoperated or off-line programmed manipulators to prevent the manipulator colliding with objects in its operating environment.
Range sensing systems for such collision avoidance applications must meet a number of criteria. For instance, the system should ideally cover the entire volume of space surrounding the manipulator. This entails the use of a number of sensor elements which therefore should preferably be small, uncomplicated and cheap. In addition, the operating speed of the sensor system must be sufficiently fast to meet the real-time control requirements of the manipulator control system.
In view of the above requirements infra red (IR) light reflection range sensing systems have been used in such collision avoidance systems. See, for example, the article "Proximity Sensing in Robot Manipulator Motion Planning: System Implementation Issues", IEEE Transactions on Robotics and Automation, Vol. 5 No. 6, December 1989.
Essentially, such IR range sensing systems use an LED (light emitting diode) as a point source of IR light to illuminate any object which enters its field of illumination. IR light reflected from the object is then detected by a suitable detector such as a photo diode. The intensity of the IR light which falls on the object, and thus the intensity of the detected reflected light, is related to the distance between the LED/detector and the object (i.e. the range of the object) in accordance with the inverse square law. The range of the object is thus computed by the sensing system as a function of the known intensity of the emitted light and the measured intensity of the reflected light.
Simple single emitter/detector IR range sensing systems suffer the disadvantage that they are sensitive to the reflection characteristics of the object. That is two different objects at the same range may reflect different amounts of the emitted IR light as a result of a difference in their reflection characteristics. The reflection characteristics of any given object are dependant upon its albedo, its orientation relative to the emitter and detector, its area in the field of illumination, and its area in the field of view of the detector. Thus sensing systems have been proposed which eliminate the dependence on the object reflection characteristics by utilising two emitters (or detectors) spaced apart on the axis of measurement (i.e. a line passing through each emitter (or detector) and the object). This yields two separate measurements for which the reflection characteristics will be identical and which can therefore be combined to give a measurement of the range of the object which is independent of its reflection characteristics.
However, the accuracy of such a system is dependant upon the separation of the two emitters (or detectors). In practice, in order to give acceptable results the separation must be a significant fraction (i.e. more than about 25%) of the maximum range that is to be measured. A typical maximum range requirement of a sensing system in a robot manipulator collision avoidance system is of the order of 500 mm, in which case the emitter (or detector) separation would have to be about 125 mm in order to achieve a desirable level of accuracy. Such known range sensing systems cannot therefore be used in collision avoidance systems without unacceptably interfering with the utility of the manipulator.
It is an object of the present invention to provide a range sensing system which obviates or mitigates the above problems.
According to a first aspect of the present invention there is provided an object sensing system comprising an array of emitters arranged with overlapping fiel
REFERENCES:
patent: 4884216 (1989-11-01), Kuperstein
patent: 4893025 (1990-01-01), Lee
Cheung, Edward and Lumelsky, Vladimir, J., "Proximity Sensing in Robot Manipulator Motion Planning: System and Implementation Issues", IEEE Transactions on Robotics and Automation, vol. 5, No. 6, Dec. 1989, pp. 740-751.
Browning Clifford W.
Hannaher Constantine
U.K. Robotics Limited
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