The invention relates to a torque sensor that can be used in drive instrumentation.
This torque sensor according to the invention comprises a freewheel with a first rotating element for transferring a torque to be determined to a second rotating element which is coaxial to the first rotating element, the transfer occurring in one rotational direction, and devices for determining a rotation of the first rotating element relative to the second rotating element in said rotational direction as well as devices for determining the torque using the determined relative rotation.
According to the invention, the torque that is causing this relative rotation can be determined using the extent of the rotation of the two rotating elements relative to one another in said direction. An advantage is that the freewheel can perform a dual function as the machine element which transfers the rotational motion and as the sensor component which produces the measurement effect. The freewheel only needs to be slightly modified in order to be used as the torque sensor.
Whereas it would be possible to directly detect the degree of rotation of the rotating elements relative to one another, in a preferred embodiment of the invention, the devices for determining the relative rotation are provided for the purposes of determining the rotational angles of the two rotating elements independent of one another.
It is useful that the devices for determining the relative rotation of the rotating elements can also find derivations of the detected rotational angles as a function of time and thereby determine the rotational velocity n of the first rotating element and the rotational velocity n′ of the second rotating element.
The device for determining the relative rotation of the rotating elements continuously compares n and n′, for example. When the rotational velocity n of the first rotating element reaches the rotational velocity n′ of the second rotating element, this indicates the beginning of the transfer of a torque. The device for determining the relative rotation of the rotating elements determines the rotational angles that have been traversed since this time, and also determines the rotational velocities n, n′. Rotational velocity n temporarily exceeds rotational velocity n′, whereupon it again approaches n′ at constant torque. When n=n′, the freewheel transfers the torque to be measured. The angle α of relative rotation is calculated from the difference in rotational angles of the rotating elements, these angles having been determined based on the time mentioned above. The torque sensor then calculates the torque to be determined using a stored relationship between the angle α and the torque.
The devices for determining the relative rotation of the rotating elements preferably comprise at least one measuring ring which is coaxial to one of the rotating elements, the measuring ring comprising a peripheral marking and a detector for scanning the marking.
The marking can be an optically scannable dashed line. However, the marking is preferably formed by a magnetization of the measuring ring, the magnetization being variable in the peripheral direction. The detector detects this magnetization accordingly.
It is useful that the measuring ring is magnetized peripherally in the form of a periodic function.