Torque limiter

A torque limiter device comprising:

• an input shaft arranged to be driven by an externally applied torque such that it rotates around a first axis, said input shaft comprising a first contact surface;
• an output shaft rotatable around a second axis, wherein the second axis is substantially coaxial with the first axis, said output shaft comprising a second contact surface that faces the first contact surface, and wherein the input and output shafts are operable in an engaged position wherein the first and second contact surfaces are brought into mechanical engagement, and a disengaged position wherein the first and second contact surfaces are separated;
• a biasing mechanism arranged to provide a bias force that biases the input and output shafts in one of the positions;
• an electromagnet arranged to provide an electromagnetic force that opposes said bias force when an activation current is passed through a coil of said electromagnet, thereby operating the input and output shafts in the other of said positions;
• a rotation sensor arrangement arranged to measure a rotation of the input shaft and a rotation of the output shaft;
• and
• a controller arranged to determine a difference between the rotation of the input shaft and the rotation of the output shaft, said controller being further arranged to selectively supply the activation current to the coil of the electromagnet such that the input and output shafts are operated in the disengaged position when the difference exceeds a threshold,
• wherein each of the contact surfaces comprises one or more grooves, wherein at least one rotatable member is disposed in at least one of said grooves, wherein in the engaged position, the rotatable member mechanically engages a respective groove on each of the contact surfaces.