Sensors enable the precise measurement of the values needed to determine the state of a drive system. Harmonic Drive® Torque Sensors determine the load situation of an actuator and help to prevent overloads or enable safe human machine interaction or force feedback functions.
Harmonic Drive® Angle Measurement Systems detect the position of the motor shaft, enabling the motor winding to be optimally energised to generate maximum torque or to execute movements with the highest precision.
Harmonic Drive® Torque Sensors
Harmonic Drive® Angle Measurement Technology
Harmonic Drive® Gears are used wherever precise movements must be executed with zero backlash. In many applications, such as robotics or medical technology, torque is needed as an input signal for sensitive motion control. By monitoring and limiting forces, the torque signal enables fundamental safety functions in collaborative robots (cobots), such as collision detection. For direct teach in, the cobot requires torque signals in all axes to support the robot's guidance with a motor. For assembly robots, torque monitoring enables precise joining of components.
By compactly integrating a torque sensor into a strain wave gear, Harmonic Drive SE offers the user an additional torque signal for safety functions as well as sensitive motion control.
Seamless integration of the sensor into the gear
Based on its internal design the sensor is loaded by pure torque, but not by bearing forces. Hence the torque signal is not influenced by bearing forces. As a consequence the sensor has a compact design and requires only minimum additional space. The tilting moment stiffness of the axis is not reduced by the sensor.
Gears with torque sensors often require customisation to ensure perfect integration into the application. The design of the core elements, gear component set, output bearing and torque sensor, are carried out by Harmonic Drive SE. These components can be individually adapted to the requirements of the application. One of the strengths of Harmonic Drive SE is its expertise in integrating strain wave gears and sensors into customer specific actuators, including the design of bearings and sealing concepts, the design of the sensor and the cable routing.
Harmonic Drive® Torque Sensors impress with outstanding measurement accuracy setting new standards. The torque sensor itself has a measurement accuracy of 0.1% of the full scale torque. In combination with the gear, a system accuracy of 1% is achieved. This enables precise measurement and, if necessary, control of the load, as required in assembly processes for example.
Harmonic Drive® Strain Wave Gears with integrated torque sensors are characterised by a high degree of robustness. The torque sensor is based on proven strain gauge technology and is therefore characterised by high temperature stability, ageing resistance and electromagnetic compatibility. Due to its robust design, it has high stiffness and overload capacity and achieves an excellent lifetime even under harsh conditions.
The torque sensor can be equipped with a variety of electrical interfaces. The sensor can be equipped with passive strain gauges with measurement electronics on customer side. Alternatively, analogue signals (e.g. ±10 V), serial bus protocols (USB, RS-232), PCB bus protocols (I²C, SPI) or field bus systems (CAN, EtherCAT) are possible.
The feedback system: the be-all and end-all of high-performance drive control
The accuracy and control performance of a servo drive depend, to a large extent, on the performance and type of connection of the feedback system. In many applications, high repeatability, high absolute positioning accuracy and good speed synchronisation are required. Particularly with highly dynamic servo drives, such as those offered by Harmonic Drive SE, precise step response behaviour is also important.
Motor feedback systems are available with a wide range of interfaces and operating principles. The first distinction is the design: a difference is made here between solid shaft and hollow shaft encoders. While the solid shaft encoder can be used in an entire product series regardless of size, in a hollow shaft system the size of the hollow shaft encoder is usually adapted for each drive size. This means a wide variety of mechanical designs (different hollow shaft diameters).
The next distinction is the principle of operation: the variance ranges from optical principles of operation to inductive and capacitive sensors, and magnetic sensors. The decision of which principle to select is based on the application, accuracy and environment.
We offer a wide range of interfaces to enable the servo drives to be operated on the most common servo controllers. The portfolio includes pure incremental encoders (sine or square wave signals), hybrid or fully digital SSI encoders, encoders with the BiSS protocol, HIPERFACE® interface, encoders with the EnDat2.1 or EnDat2. 2. A hybrid feedback system is an encoder that transmits the absolute position via the protocol and the rotary motion via sine and cosine tracks.
In conjunction with the Harmonic Drive® Gear, multiturn encoders are primarily used, which can typically detect 4096 revolutions of the motor shaft
Due to their high gear ratio and precision, Harmonic Drive® Servo Actuators increase the resolution provided by the encoder by the gear ratio factor. This means that the resolution on the output side is many times higher than on the motor side.
However, even the zero backlash Harmonic Drive® Gear cannot prevent one thing: different loads generate corresponding torsion on the output side. To compensate for this load dependent torsion, Harmonic Drive® offers the option of integrating a high resolution output side encoder into the servo drive. This is connected directly to the output flange via the hollow shaft. This means that the application can be positioned with an accuracy of a few seconds of arc, even with changing loads.
Harmonic Drive® Servo Actuators not only offer the highest precision, but they are also extremely robust – even in the smallest of spaces. We take this into account with dirt resistant feedback systems that are also suitable for low and high ambient temperatures and resistant to shock and vibration. For this purpose, we offer special feedback systems that are characterised by a high level of robustness due to their operating principle – for example, capacitive, inductive or magnetic sensors. This has the advantage that dirt and moisture, as well as vibrations and shocks, have no influence on the precise angle measurement.
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