Patent ID: 6943565

Claim:
A robot arm for industrial robots, comprising one or several jointed arms ( 1 , 1 c ) that are mutually connected to each other by means of rotary joints ( 1 a , 1 b ), and a jointed arm ( 1 ) connected to a base ( 3 ), wherein an angle transducer ( 4 - 7 ) is arranged in the rotary joints ( 1 a , 1 b ) in order to measure exactly the angular relationship between the jointed arms ( 1 , 1 c ) or between the jointed arm ( 1 ) and the base ( 3 ), in order to make possible adjustment of the robot arm into a desired angular position, wherein the angle transducer comprises a first disk, the rotor ( 4 ), with circularly arranged and radially directed receiver electrodes ( 5 ) and a second disk, the stator ( 7 ), equipped with circularly arranged and radially directed transmitter electrodes ( 6 ) arranged at the same radius as the receiver electrodes ( 5 ) and with a fixed separation between the receiver electrodes and the transmitter electrodes on the two disks, whereby the disks ( 4 , 7 ) are arranged coaxially and rotatable relative to each other, and the disks are further separated by a thin air-gap that makes possible a capacitive or an inductive coupling between the electrodes ( 5 , 6 ) on the rotor disk ( 4 ) and the stator disk ( 7 ), characterised in that the transmitter electrodes ( 6 ) are each supplied with an alternating voltage with different phases for neighbouring electrodes, whereby the number of supply phases, Φ, is greater than two, and the separation of transmitter electrodes=the separation of receiver electrodes/Φ, and that the transmitter electrodes ( 6 ) of the stator are geometrically arranged such that errors in their geometry relative to the geometry of the receiver electrodes ( 5 ) produce equal but opppsite error signals in the receiver electrodes ( 5 ) of the rotor.