A magnetostrictive torque sensor is a type of sensor used in robotics to measure torque applied to a mechanical system. It utilizes the magnetostrictive effect, which is a property exhibited by certain materials that causes them to change shape when subjected to a magnetic field. This effect is reversible, meaning that when the magnetic field is removed, the material returns to its original shape.
Here's an explanation of how a magnetostrictive torque sensor works in robotics:
Construction: The sensor consists of a ferromagnetic material rod or shaft, typically made of a nickel-based alloy, which acts as the primary sensing element. This rod is placed along the axis of the shaft whose torque is being measured.
Magnetostrictive waveguide: Inside the ferromagnetic material rod, a magnetostrictive waveguide is installed. The waveguide is usually a thin wire or a small strip of a magnetostrictive material, such as Terfenol-D.
Magnetic field generation: At the ends of the ferromagnetic rod, magnetic fields are generated using coil windings or permanent magnets. These magnetic fields induce a change in shape (strain) in the magnetostrictive waveguide.
Torque application: When torque is applied to the shaft, it causes a torsional deformation in the shaft. This deformation is transmitted to the magnetostrictive waveguide.
Strain measurement: As the magnetostrictive waveguide experiences mechanical strain due to the torsional deformation, its length changes accordingly. This change in length results in a change in its magnetic properties. The speed of a torsional wave traveling along the waveguide is affected by the magnetic properties of the material.
Detection: At one end of the waveguide, a magnetostrictive sensor is placed. This sensor emits a short-duration magnetic pulse that travels along the waveguide. As this pulse reaches the other end of the waveguide, the changed magnetic properties are detected by the sensor. The time it takes for the pulse to travel back to the sensor is directly proportional to the mechanical strain experienced by the waveguide.
Torque measurement: By measuring the time of flight (TOF) of the magnetostrictive pulse, the degree of torsional deformation (and thus torque) applied to the shaft can be calculated. The relationship between the TOF and the torque is determined during the calibration process, where known torques are applied, and the corresponding TOF values are recorded.
Output: The sensor's electronics process the TOF information and convert it into a torque value, which can be further used in control systems or displayed to the user for monitoring and analysis.
The magnetostrictive torque sensor's non-contact nature and high precision make it well-suited for various robotic applications where accurate torque measurement is critical, such as robotic arms, manipulators, and force-controlled robots.