EHCDs (electro-hydraulic control decentral), their applications and use cases, and HYDAC’s parameter configuration tool are focus areas in this presentation.
What is an EHCD?
EHCD is a configurable control device for electro-hydraulic systems that comes in different types (simple power amplifier, general control modules, closed-loop controllers and synchronised control).
In our EHCD range we have many devices from analogue devices that can be configured using potentiometers to digital, parameterisable and programmable devices.
For example, we have PWM amplifiers, special pressure force and flow controllers, position synchronisation modules and Profibus and Profinet options.
The analogue module is simple to use but it doesn’t offer a lot of customisation and it has to be configured via a potentiometer. Therefore it may not be the best option for certain applications. In view of that I recommend our digital range.
However, before applying any products in the digital range it’s important to read the documentation that accompanies each device, particularly the safety information to ascertain if the device suits the application.
These modules are suitable when you have a simple automation system, you don’t have a PLC and you need complex closed-loop control or closed-loop control (pressure, force and flow). Another scenario is when you have a PLC without power stages or you need to execute synchronisation and position control.
One use case is a simple but complex scenario where you have a system but you need to execute closed control without requiring a lot of automation or sequencing. In this instance you may or may not have access to a PLC or PLC functions are limited.
The requirement in this case is that you perform complex and precise closed-loop control, repetition and positioning. In this scenario the EHCD module is a good option.
There are different EHCD modules available depending on the required application.
Once you select the module for your application you can program and configure it using parameterisation software. The software is available for free and has a great and easy to use graphical interface. The graphical interface allows you to easily set parameters, monitor the inputs and outputs in real time, and take manual control of the actuator.
As to analogue inputs, they come from 4-20mA and 0-10V, potentiometers which you can scale using the parameterisation software. Communication interfaces are also available such as Profibus, ProfiNET (trademark/copy protected names), EthernetIP and IO Link. So again you’ve got this really good option if you don’t have a PLC and you have to do something complex.
Within the software result you can customise your amps, you can execute linearisation if you have a coil or a valve that's not responding linearly, and you can limit your outputs for your valve control limitation.
We also have a power stage to perform the PWM signal to the valve. Most hydraulic valves are operated using a PWM signal with a constant frequency and a varying duty cycle, with these modules producing the PWM signal.
If you have two valves, we have a really nice feature being an enable input for valve A or B or coil A or coil B.
It ensures that the valves will not turn on until the interlocks in the system are met.
The other potential is you have a PLC in your project but it doesn’t have a PWM output. Generally PLCs have zero to 10V or 4-20mA outputs and when you try to put that onto a PWM valve nothing happens unless there's a valve that has on-board electronics.
Here the solution is to put in an EHCD module in between, take the 4-20mA signal from the PLC, scale your input and the module will produce the PWM output and drive your cylinder or drive your motor, pump or whatever it is you want to control using that EHCD module.
Another use case is that if you need precise closed-loop control to accurately control the pressure or the force you're applying to a system.
In this instance these modules are a really good option because you can attach a pressure sensor and it'll feed straight back in to control the cylinder. And within the module there are a lot of really nice features for PID control and PID tuning optimised for these types of applications.
You can remove this functionality from a PLC and just have it standalone on the module. An application example here is when you need to apply a constant force or when you want to strain some iron strains from sheet or for a press or the like.
You don’t have to write the logic in the PLC for this type of application – you can leave it up to the EHCD module, which is designed to execute closed loop PID control.
Another application or use case is when you need to position and synchronise control. We have modules for when you need to move multiple cylinders at the same speed or at the same time or when you need to drive constantly to a specific position, as examples. In these instances it is possible to get cylinders that have position sensors inside and you can run the feedback of this analogue signal directly into the EHCD module and then just control the controller position.
For example, in timber mills you need to drive saws to particular positions repeatedly, and then to new positions. In this instance the device can perform its own precise PID control.
Parameter configuration tool does the trick
HYDAC’s parameter configuration software is a nice tool as evident in the many requests we receive for PLC projects and the like.
Most of the time these modules can perform the functions of a PLC if complex automation requirements are not needed. The software is free and available for download from hydac.com/de-en (click on ‘downloads’, ‘software’ and then ‘systems engineering’).
Once you have your device connected, all the settings possible for that device will appear. It’s really easy to use as it’s table-based parameter input, with all options listed corresponding to the device’s manual.
Analogue input scaling comes in handy when you want to chop your analogue signal some more. Again you can customise your ramps for this particular application; if you perhaps need to extend the cylinder over five seconds and then pull it back in faster or slower you can do that with ramp time.
The maximum current is stipulated on the datasheet of the hydraulic valve of the coil that you use, and that information is entered from the datasheet. When control is taking place at really high frequencies dithering is available for high frequency valves if required. It is also possible to set your own PWM frequency, which comes from the datasheet.
This entails taking note of the datasheet of your coil or valves when setting up these valves. Again table-based input makes it really simple. And we have the old PID settings, with no further settings available.
These settings can be saved and deployed onto multiple devices, which makes for ease of use.
A really nice feature within the software is the oscilloscope function that enables you to see what’s happening in with the application/ actuator in real time.
The other really nice feature is ‘live view’ remote control mode. This means that if you have configured the device you can drive it manually. This gives you a really nice way to see if your PID is responding correctly to whether there’s an issue with the hydraulics or the control loop etc. Please note that any interlocks or external safety controls that you have in place are ignored if in this mode as you’re controlling the valve directly.
The software is free and easy to use as it links in directly with the manual of the device you intend to use.
Different types of modules
Universal plug amplifier
The universal plug amplifier, which sits directly on the valve coil, will produce a PWM output directly onto the valve if you send it a 4-20mA signal or 0-10V.
It’s a really tiny device that’s programmable using the same software. In this regard we also have IO Link options available.
With the USB configuration tool you can program in ramps your minimum and maximum scaling.
Universal digital amplifiers
Universal digital amplifiers are common to many applications. With this device you can control one or two valves directly by analogue or digital outputs with free parameterisation of ramps, minimum and maximum output current, dither (frequency, amplitude) and PWM frequency.
Four quadrant ramps enable you to select how quickly you want the actuator to respond. Other features include application orientated parameter settings via USB interface, free scaling of analogue inputs, linearisation of solenoids via 10 XY points per solenoid and failure monitoring.
It’s evidently quite a flexible little module. Proportional valves can be controlled with one or two solenoids by three digital inputs and signals to select up to eight pre-programmed command and ramp values.
The same module has the ability to change the functioning of the module and even control one directional valve using a +/-10V or 4-20mA cable monitoring input signal.
You can use it to control two different valves independently, and each one of them can have its own ramps, minimums and maximums and inputs.
So it’s quite a Jack of all trades’ device that’s usable in many applications.
Pressure control modules
The pressure control module, designed for accurate closed-loop pressure control application, is one of our more speciality modules.
We also have modules which allow you to control force and pressure accurately aka Q-P control.
We have a lot of other special modules available such as
positioning modules for when you need to drive a cylinder to a particular position, hold it there, and move it backwards and forwards when required.
We also have ones with SSI feedback from linear position sensors installed inside the cylinder which can feed directly back into this module and enable acceleration and deceleration control.
Other features include set point, actual value, control and feedback; actual position feedback via SSI sensor or analogue; and position resolution up to 0,011mm (SSI).
Position synchronisation control modules
Our synchronisation modules are a really good example if you need to lift up a working platform and you have two cylinders (up to four cylinders can be synchronised with the main module).
Here you can have control and feedback via a Profibus – once again a really nice feature if you have complex motion control requirements.
In summary it’s clear to see that these modules are flexible, easy to configure and use and suitable in many applications.
The modules are also available with Profibus, Profinet, EthernetIP, Ethercat and IO Link.