Signal motors mainly include two categories: position signal motors and speed signal motors. Rotary transformers, inductive synchros, and synchros are all position signal motors, while tachogenerators are the main type of speed signal motors.
I. Position signal motor
1. Rotary transformer
A rotary transformer is an AC control motor that operates on the principle of variable coupling. Its secondary output voltage has a definite functional relationship with the rotor angle. Essentially, it is a transformer that can arbitrarily change the coupling degree between the primary and secondary windings, and is used in SA37 reducers. Its structure is the same as a wound-rotor induction motor, with two sets of mutually perpendicular distributed windings on both the stator and rotor. The rotor windings are connected to the external circuit using slip rings and brushes. After the primary winding is energized, the output voltage of the secondary winding has a sine, cosine, linear, or other functional relationship with the rotor angle. This relationship can be used for coordinate transformations and trigonometric operations in computing devices, and can also be used as an angle data transmission and phase shifter in control systems.
2. Inductive Synchronizer
An inductive synchro is a high-precision position or angle detection element, available in two types: disc and linear. Disc-type inductive synchros are used to measure angular position, while linear inductive synchros are used to measure linear displacement.
3. Synchro
A synchro is an AC control motor used for transmitting, receiving, and converting angular displacement information. It is a general term encompassing a synchro transmitter, synchro receiver, synchro differential transmitter, synchro differential receiver, and synchro control transformer. This type of worm gear reducer is widely used in servo systems as a device for angle transmission, conversion, and indication. In control systems, two or more units are often used in combination to enable two or more mechanically unconnected shafts to automatically maintain the same angular change or rotate synchronously.
II. Speed Signal Motor
The most representative speed signal motor is the tachogenerator. A tachogenerator is an electromagnetic device that detects the rotational speed of machinery. It converts the rotational speed into a voltage signal, and its output voltage is proportional to the input rotational speed. In the automatic control system and computing device of a VEMT gearbox, it is commonly used as a speed measuring element, correction element, calculation element, and angular acceleration signal element. Essentially, it is a mechatronic element that converts rotational speed into an electrical signal. From a working principle perspective, it falls under the category of "generator." In control systems, tachogenerators are mainly used as damping elements, differentiating elements, integrating elements, and speed measuring elements.
Tachogenerators are classified as DC or AC; DC tachogenerators are further divided into separately excited and permanent magnet types. Their structure and working principle are the same as low-power DC generators, typically with lower output power. When used as a computing element, their output voltage linearity error and temperature error must be below a certain upper limit. AC tachogenerators are further divided into synchronous and asynchronous types.
Synchronous tachogenerators include permanent magnet, induction, and pulse types; the most widely used asynchronous tachogenerator is the cup-rotor asynchronous tachogenerator. To improve the accuracy and reliability of tachogenerators, brushless Hall effect DC tachogenerators have emerged. Because this Hall effect brushless DC tachogenerator is a slotless, winding-free motor, it does not generate "cogging harmonic potentials" caused by cogging. This type of motor has a simple structure and is easy to miniaturize.
