The combination of hydraulics and pneumatics with electronics
Fluid power has been around for decades. We may come across hydraulics and pneumatics on a daily basis and may never realize it. Whether it’s the refuse truck picking up our trash, the lift of an elevator or the brakes on a roller coaster, we have become accustomed to the sights and sounds of fluid power. The power of hydraulics and the speed of pneumatics are a force that drives our society and economy. They provide for us a method to efficiently transfer energy to do usable work. However, a knock against fluid power has been its ability to provide precise, accurate and repeatable control.
Electronics, as a control technology, has also been around for decades. In this day and age, electronics are a must-have in our daily lives. Whether it’s driving through the automated car wash, engaging in social media on the cell phone or getting some cash out of the ATM, life becomes very difficult when the power goes out or we become “unplugged”. The feasibility, versatility and functionality of electronics are irreplaceable in our daily lives. It provides us with a method to precisely control the flow of electrical current to efficiently do the work at hand. However, a shortcoming in electronics has been the inability to match the power provided by fluid power.
Combining fluid power strength with electronic finesse has been a major contributor to advances within our industry over the past couple of decades. This marriage, commonly known as electro-hydraulics or electro-pneumatics, has proven to be very fruitful as new applications and technologies have developed. Whether it’s using proportional control for hydraulic actuators or fieldbus programming for the control of pneumatic valves, this combination has proven to be highly beneficial in providing precise, accurate and repeatable control of heavy loads, fast speeds and the transfer of energy.
Although it took the industry some time to realize these benefits and put them to meaningful work, the commonality between fluid power and electronics is impressive. Take a look at the following parallel paths of fluid power and electronics.
- Fluid power uses pipe, tube or hose as a conduit through which fluid medium flows, while electronics uses wire as a conductor through which current flows.
- Flow in fluid power is the movement of fluid molecules measured in volume per unit of time (e.g. gallons per minute, liters per minute), while flow in electronics is the measure of passing charges per unit of time (i.e. current).
- Pressure in fluid power is a hydrostatic force which motivates the fluid molecules to move from a point of high pressure to a point of low pressure, while the voltage in electronics is the electrical force which motivates the charges to move from a point of high voltage to a point of low voltage.
- Fluid power uses a flow meter for measurement of fluid flow, while electronics uses an ammeter to measure electrical current.
- Fluid power uses a differential pressure gauge to measure the pressure difference between any two points in the system, while electronics uses a voltmeter to measure the voltage difference (i.e. electrical potential) between any two points in a circuit.
- Fluid power uses an orifice to oppose the flow of fluid, while electronics uses a resistor to oppose the flow of electrical current.
- Fluid power uses an accumulator to store energy, while electronics uses a capacitor to store electrical charge.
- Fluid power uses a check valve to allow free flow in one direction but not the other, while electronics uses a diode to allow current in one direction but not the other.
- Both fluid power and electronics provide us with a way to assemble parts to allow for one or more continuous flow paths to perform discrete functions.
How Do They Work?
Electro-hydraulic or electro-pneumatic systems are an assembly of several components such as pumps, compressors, valves, regulators, motors, cylinders and so on, that are electronically controlled. These components are connected together in ways that will do the particular work at hand.
Electro-hydraulics and electro-pneumatics include different types of electrical signals. An input signal is a signal that is coming into a device, while an output signal is the resulting signal coming out of a device. A proportional output is one in which the output is proportional to the input. An analog signal is a signal that varies over a range of values, while a digital signal is a signal that consists of coded single-value digits (e.g. yes/no, on/off).
There are several different types of electro-hydraulic and electro-pneumatic systems. A closed-loop system is one in which the output signal is fed back to the input so that the input can be modified automatically as much as necessary to maintain the desired output. This system will include feedback devices such as transducers, monitors and so on. A proportional-integral-derivative (PID) controller allows components to control their feedback by calculating the error value between the measured and desired set-point, and minimizing this error by adjusting the process control inputs. An open-loop system is one in which the output signal is not fed back to the input signal. Unless there is a requirement for feedback monitoring, most electro-hydraulic and electro-pneumatic systems are open-loop in which the operator must adjust the input to maintain the desired output.
The future of electro-hydraulics and electro-pneumatics is bright. Newer, “intelligent” systems are constantly on the horizon. Industry has come to this realization over the years and is moving in this direction full steam ahead to capitalize on new opportunities. Component manufacturers have begun to offer products that can integrate easily with different types of electronics, many now incorporating embedded electronics. Distributors and integrators have developed expertise in identifying new applications and applying the latest technologies. Organizations such as the International Fluid Power Society have recognized this change by adding more certifications such as the Fluid Power Electronic Controls Specialist.
As discussed above, there are many commonalities between the worlds of fluid power and electronics. With the combination of electro-hydraulics and electro-pneumatics, we are able to use the best of both worlds. Fluid power technologies provide the muscle in transferring energy into work and electronic technologies have added new levels of control to complete the task at hand. Like any marriage, these two technologies complement and need one another.
Note: “Tech Tips” offered by Flodraulic Group or its companies are presented as a convenience to those who may wish to use them and are not presented as an alternative to formal fluid power education or professional system design assistance.
Experts in fluid power, electrical and mechanical technologies.