Determining the start date of motion control greatly depends on your definition of motion control. An argument could be made that it started with the invention of the mechanical cam. Others might say it didn't start until PID control was introduced.
There's no definitive beginning, but we're just going to start with electric motors, just under 150 years ago. You can read a more extended history of motion control here. In this article, we will explore the development of technologies that made modern motion control possible.
All the Right Tools
While the electric motor had been invented since 1837, it wasn't commercially viable until Zenobe Gramme unveiled his design of the DC motor in 1873. Years later, Tesla, the champion of AC current himself, came out with his own AC induction motor. Since then, electric motors were being used in more and more devices.
By the time 1914 rolled around, the use of interchangeable parts had become much more commonplace, and Henry Ford had just installed the first mechanized assembly line. Efficient manufacturing was on the rise. And good thing too, as the world was diving right into the First World War.
With the assembly line, electric motors, and war-driven innovation, the age of automation was rapidly approaching, but there was one key component missing for motion control…
Feedback: The missing piece
In a sense, control feedback itself had already been implemented by the 1900s. Thermostats and centrifugal governors had been used for furnaces and steam engines respectively in the centuries previous. But the idea of using a negative feedback loop to tighten control had not been truly mapped out, even as World War I ended and we entered the Jazz Age.
Then one day on his ferry ride in 1927, Harold Black jotted down some notes on using a portion of a power amplifier's output to negate some of the input and reduce the signal distortion, particularly for long range communications. His invention of the negative feedback amplifier set the groundwork for amplifiers moving forward. Soon, negative feedback loops were introduced into both pneumatic and communication devices everywhere.
In the same year that Harold Black published his paper on the negative feedback amplifier, Harold Hazen similarly recognized that negative feedback could be used to adjust the response curve of a servomechanism. Moving forward, the works of both Harolds would be crucial in developing motor control techniques. Electrical motion control was born.
Even with a negative feedback loop, however, control systems were still not refined. Using purely proportional control was very susceptible to initially overshooting the target output and requiring time to level off and find stability. It also didn't respond well to sudden disturbances. There was still much work to be done before servo amplifier technology would start looking like it does today.
PID: A Game-Changer
The implementation of PID control changed everything. PID stands for Proportional, Integral, and Derivative, and refers to the different gains that are applied in an amplifier to correct for error in a closed-loop system. A signal amplified with PID produces a much smoother response than one amplified with proportional control alone. The integral control component eliminated steady-state error and the derivative component reduced the response overshoot. The idea of PID had existed as a mathematical theory since J.C. Maxwell Wrote about in 1886. However, it would be about half a century before it was integrated into technology, at least on purpose.
As World War II wrapped up, controllers with electrical systems started to become more commonplace. These would see great improvement over the next few decades. With the Cold War, countries pushed technological innovation, as no one wanted to be disadvantaged if open war broke out. Eventually, PID control technology and servo amplifiers would aid in the United States' mission to put a man on the moon.
The Age of Analog
The technological developments of the 60s and 70s yielded solid state electronics, including semiconductor transistors, enabling high frequency switching. Around the same time, pulse width modulation (PWM) was developed as way to send electrical signals far more efficiently. These advancements made it possible to activate and deactivate multiple motor phases in a controlled fashion. We had entered the era of DC brushless motor control.
Analog servo amplifiers were becoming more compact and more advanced simultaneously. Features such as status indicators, multiple operating modes, and support for multiple feedback devices started coming in panel mount and PCB mount servo amplifier packages.
It's worth noting that the motion control industry would be forever changed (in our opinion) when Sandor Barta and Daniel Schoenwald started ADVANCED Motion Controls in 1987, building analog servo amplifiers on a kitchen table in Van Nuys.
The Rise of Digital
Digital electronics began to take hold in the 1970s. Integrated circuits, microprocessors, non-volatile memory, and inter-networking began to shape the landscape of electronic technology as we know it today. More and more industries started transitioning from analog to digital.
Digital made headway into the motion control industry in the 1990s. With the invention of digital servo amplifiers, or digital servo drives as they are now more commonly known, the possibilities in motion control greatly expanded. Digital servo drives could now use position feedback to move a motor's rotor to specific positions, rather than just torques and velocities. Digital servo drives could also be run over a network and communicate amongst themselves and other devices with i/o (input/output) signals.
In recent years, the line between motor controller and amplifier has become very blurred. Servo drives have their own processing power now, allowing them to do more of the work normally required by an external controller. Their built in memory allows them to store movement profiles, again reducing the controller's workload and sometimes entirely removing the need for it.
A significant portion of the motion control business remains in analog, but the industry becomes more digital with each passing year. You can read more about the differences between digital and analog servo drives here.
While the base technology of motion control is now very well established, the industry continues to grow and evolve. If you're curious as to where the motion control industry is headed, then read Servo Drive Trends for 2020 here.
by Jackson McKay, Marketing Engineer
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