The DC Servo Motor Control System: History And Uses
Any AC or DC servo motor control system can trace its origins to James Watt’s ‘Steam Engine Governor’, which is widely held to be the first powered feedback system in history. However, given its lack of an amplifier or gain, the Steam Engine Governor can not properly be referred to as a servo mechanism or servo motor.
The first fully closed-loop, feedback-based positional control device was the steering engine, which was a technology first used on the SS Great Eastern in 1866, purposed to the positioning of the rudder of this very large vessel. Such steam steering engines possessed all the characteristics of a proper servomechanism, namely an input, an output, an error signal, and some method by which the error signal could be amplified fur use as negative feedback to help drive the measure error down to zero.
For electrical servomechanisms to function, they require a power amplifier. With the advent of World War II, the world saw the development of fire-control servomechanisms that utilizes amplidynes to serve as power amplifiers. Operating in a somewhat more peaceful fashion, the UNISERVO tape drive for the UNIVACI computer used vacuum tube amplifiers.
The key thing to keep in mind when surveying these historical antecedents of modern AC and DC servo motor control systems is that servo motors are not necessarily tied to any particular technology. The term ‘servo motor’ is merely used to describe a particular type of feedback circuit, which may be built of components using steam, hydraulics, electricity or any other substance capable of doing work or of reacting to relevant changes in the external environment.
Nonetheless, the majority of modern servomechanisms, including those used in DIY robotics and RC home kits, make use of solid state power amplifiers than tend to be built from either thyristor or MOSFET devices. Due to the fact that they function as entirely electronic feedback circuits, they can be controlled remotely or, if desired, by means of a cable connected to your PC via its USB port. The benefits of having a solid USB connection are numerous. This is especially so when going through the initial stages of development for basic robotics, as it removes any issues in terms of reception or transmission while working on matters of actuation, issues that can be tackled on their own later in the day.
RC servos are actually the preferred means of control in small scale robotics applications even at such lofty institutions as MIT and Stanford. This is primarily due to their affordability, their simplicity of control (achieved by means of microprocessors), and, due to their reliance on relatively unsophisticated technologies, their reliability when compared to more advanced robotics.
Your typical RC DC servo motor control system consists of an electric motor which is mechanically linked to a device known as a potentiometer. The potentiometer in turn sends a PWM (pulse width modulation) signal to the servo, a signal that is in turn translated into a positional command by means of the electronics within the servo motor. So, for instance, when the servo receives the specified signal that commands rotation, the motor is powered until it reaches the value that the potentiometer reads as corresponding to the desired position.
If you’re looking to develop your own basic DC servo motor control system, you’d probable best take a squizz through the pages of one of the RC specialty magazines, such as Make or Bot. In terms of instructions as to the DIY construction of servo motors, well, frankly, the geek population known for engaging in DIY servo motor construction is probably the most online-oriented subculture in the world, so a little persistent googling should yield up any knowledge you may be lacking.
