In Early 2009 Control Devices Engineering was approached by Bosch Rexroth in Queensland to provide a custom solution for an application that involved two single axis joysticks which would control a single Bosch Rexroth RA2 Amplifier. The amplifier was to control a canting keel on a racing yacht, the keel was designed by Simon Flitcroft of DDC (Design Drafting Consultancy) in Queensland Australia. (Video of Sanity Clause in Action)
We have been lucky enough to receive great support from all the parties involved, and we do highly recommend that you contact these parties in regards to the relevant sections of this project. They are all an excellent source of information, and provide quality product and service to all of their customers.
I rarely give personal endorsements. I would only put forward people who are excel at their work and provide nothing less than exemplary service. My working relationship with the parties mentioned in this article has always been a pleasant and productive one. (Author – Mark Dzidowski)
Bosch Rexroth Proportional Valves and Amplifiers
The majority of the hydraulic control system was provided by Bosch Rexroth in Queensland Australia, the contact for this project section is Mr. Geoff Kirton, his details are provided at the end of this section of the article as well as at the end in the sources section.
Mr. Curtin has been kind enough to provide us with insight into the hydraulic system and it’s component parts. The information provides an overview of the product and technology provided by Bosch Rexroth. The following are extracts of information provided by Bosch Rexroth for this article.
Proportional Valve Technology
Acting as the linking element between switching and closed-loop technology, proportional valve technology has today become an established component part of hydraulic systems. Industry has been quick to implement the advantages offered by this technology.
How Does a Proportional Hydraulic System Work?
Please see the the diagram labelled Proportional “Valve Technology” in reference to the points below. Please click on the image to enlarge.
- An electrical input signal in the form of a voltage (mostly between 0 and ±9 V) is converted into an electrical current in an electronic amplifier corresponding to the voltage level, e.g. 1mV = 1mA.
- Proportionally to this electrical current as the input variable, the proportional solenoid produces the output variable – force or travel
- These variables, i.e. force or travel, acting as the input signal for the hydraulic valve, signify proportionally a certain flow or pressure.
- For the actuator and therefore also for the working element of the machine this means, in addition to variable direction, infinitely variable control of speed and force.
- Simultaneously, acceleration or deceleration can be infinitely varied, e.g change in flow with respect to time.
Proportional Valve Technology
Proportional valves and pumps with their proportional solenoids provide perfect interface for electronic control, thereby facilitating increased flexibility in the operating cycles of production machines as well as freely programmable control systems and drives.
The technical benefits of proportional devices can primarily be found in the controlled transfer during valve change-over, i.e. the infinitely variable control of command signals and the reduction of hydraulic equipment requirements for certain control applications. This therefore also represents an effective contribution to reducing material requirements in hydraulic circuits.
Proportional directional valve, type 4 WRZ, electronic controls type VT3000
Proportional valves permit faster, simpler, and more precise movement cycles while at the same time improving the reversal process. As a result of controlled spool cross-over, pressure peaks are avoided- resulting in a longer service life of the mechanical and hydraulic components.
The fact that the signals for direction and flow or hydraulic pressure are provided by electrical means has made it possible to arrange the proportional devices directly on the loads, thereby greatly improving the dynamic characteristics of the hydraulic control system.
Proportional devices in hydraulic systems found mote widespread use when effective devices of simplified design were offered on the hydraulics market. These devices do not greatly differ from those of the standard hydraulic range. It has also been possible to adopt a great number of parts or assemblies from the standard hydraulic range of equipment.
Force-controlled proportional solenoid
Proportional solenoids represent the linking element between electronics and hydraulics. The proportional solenoids are a form of DC linear solenoids. Proportional to the electrical current as the input variable, they produce force and travel as the output variable.
Corresponding to the practical application, a differentiation is made between:
- Solenoids with comparatively linear stroke/current relationship over a reasonably long stroke length, the so-called “stroke-controlled solenoids” and
- Solenoids with particularly defined force/current relationship over a very short stroke, the so-called “force-controlled solenoids”
Only DC linear solenoids can be used for the current-proportional change in the output variables force and stroke. Due to their stroke-dependent current consumption, AC solenoids must assume their final stroke position as soon as possible.
The solenoid force is controlled by the change in current I in the force-controlled solenoid without the armature of the solenoid performing a measurable stroke. Due to current feedback in the electrical amplifier, the solenoid current and therefore the solenoid force are kept constant even if the resistance changes.
- The main feature of the force-controlled proportional solenoids is the characteristic force-stroke curve.
- The solenoid force remains constant over a defined stroke range at constant current.
- The stroke for the solenoid shown in this example is approx. 1.5 mm. The solenoid is used in this range.
Characteristic force-stroke curve of force controlled solenoid
The force-controlled solenoid is of compact design due to the short-stroke. In view of this short stroke, the force-controlled solenoid is used particularly for pilot-operated proportional directional and pressure control valves with the solenoid force being converted into hydraulic force. The proportional solenoid is a controllable “wet pin” DC linear solenoid contained in an oil bath.
The information above was provided by:
General Manager QLD
Bosch Rexroth Pty Ltd ”The Drive & Control Company”
30 Paradise Rd
Acacia Ridge (BRISBANE) QLD 4110
Phone : +61 (0)7 3272 3555
Mobile : +61 0408 734 947
Fax : +61 (0)7 3272 3999
email : firstname.lastname@example.org
Web : www.boschrexroth.com.au
The products supplied for this project by Bosch Rexroth are:
RA2 Proportional Amplifier (Download Data Sheet Here)
We tend to use the RA2 amplifier where possible due to its competitive price and its compatibility with the full range of Rexroth proportional directional, pressure and flow control valves, as well as our range of electronically controlled variable displacement pumps. (Geoff Kirton – Bosch Rexroth)
Load-sensing control block Type SP-08 (Download Data Sheet Here)
For more information about this project and general help, advice and great Hydraulic Products please contact Bosch Rexroth on the contact details above, for further information on this project please keep reading, the next stage of the project is provided by Simon Flitcroft of DDC.
Canting Keel Design and Setup
The design required for a joystick to be mounted on either side of the yacht so that during the sailing event, access to the joystick was easily reachable. Both joysticks performed the same function, which was to swing the keel between port and starboard. We have added an extra function which would assign a master and slave arrangement, whereby the master signal took precedence over the the slave signal, ensuring that only one joystick would take command at one time.
The original concept was created as a hand etched PCB which used relays to determine the mater slave arrangement. We borrowed an RA2 amplifier from Bosch Rexroth in order to bench test the design.
We originally intended to power the system from from the RA2 amplifier 8V excitation voltage, however the output was not interned to power relay coils and it’s maximum current capability on the control side was not sufficient enough to power the unit. We had decided to add a linear voltage regulator and draw the current from the main 24V supply.
Hand Etched PCB prototype for Master/Slave command module.
We have also discovered that the current capabilities of the 8V excitation was not sufficient enough to keep good linearity of the control signal back to the amplifier. Essentially we were asking too much of the excitation voltage supply, so we decided to provide our own excitation.
Naturally we had a temperature problem because of the linear voltage regulator was stepping down from 24V to 8V to supply the control voltage for the relays and the excitation voltage to the joysticks. To solve the problem we provided a heat-sink on the prototype PCB to cope with the heat of the regulator.
We were also asked to provide a function to control a relay that provided power to the hydraulic pump. The function was to turn on whenever the joystick was to be displaced. We used a simple transistor to provide a path to ground for the relay to achieve this function. The function was triggered by the same directional switches that control the master/slave functions.
The prototype coped well in the environment however we discovered that the RA2 amplifier shows an error if the excitation output is not connected to a load. Even though the output amplifier is working correctly, it still displayed a red LED error state. The solution was to tie the output to ground through a 5K resistor.
The final version of the board was encased in a watertight housing that incorporated the slight short falls of the original prototype. We have removed the linear power supply and replaced it with a switch-mode power supply thus eliminating the heat issue. We have also provided terminals for all the cabling in the system and placed the 5K resistor that is used to tie the RA2 output to eliminate the error state on the PCB and added a cable terminal.
Final Production Version of the Master/Slave Module
The joystick that was paired with this device is the Penny and Giles JC120. It was selected because it can be supplied with a rubber boot that covers the whole joystick and is suitable for outdoor marine application. We would like to also point out that the board will work with any of the Penny and Giles potentiometer joysticks, essentially is uses a voltage divider circuit and the directional switches within the joystick to control the PCB functionality.
An example of the wiring used to connect the RA2 amplifier, PCB and 2 joysticks is provided here (Connection Drawing)
Earlier this year we were approached by Robert Jordan (R.J. & D.E. Jordan Ltd.) for a solution similar to the Sanity Clause project. Although the main function of the master/slave signal was required, additional functionality needed to be added to the system in order for it to work.
The system had one proportional flow control valve, a directional valve and a on/off valve. The system required that the joysticks controlled not just the proportional control RA2 amplifier but also the directional and on/off valves. The directional valve was controlling the anchor winch and the on off valve controlled the pot winch. The joystick requirement was for one centre spring return joystick for the anchor winch control and a friction joystick for the pot winch.
Rough Design Flow Map
We were provided with a rough sketch of what was required, we have recreated the original drawing on a digital format for the readers viewing pleasure.
The solution which was originally provided to the customer as a prototype consisted of three boxes. One contained the Master/Slave board, the second contained a patch filed and wire distribution, and the third contained the mosfet control for the directional solenoid and the on/off solenoid. Considering the joystick only had a directional switch which worked from the centre position, we also needed to include a function that monitored the output of the friction, stay put joystick, and activated a switch signal that controlled the solenoid associated with the friction joystick at the beginning of the joystick stroke. In this scenario we were using the friction joystick in a manner that used a single direction joystick that worked from one end to the other. Essentially its a speed lever accross the whole stroke of the joystick instead of the centre being the neutral voltage. Prototype Drawing
The problem with the original prototype was the complicated wiring set up where we were using three different types of PCB’s in order to achieve the desired result. We also decided to remove the mosfets and replaced them with relays that can handle far more current than the mosfets could. We also increased the size of the PCB and enclosed it in a sealed box and included fuses and polarity protection in the design. The three boards were amalgamated into one PCB thus reducing the amount of wires which required termination.
Joystick Master Slave PCB with Control Relays
The final version of the board was installed on the vessel. It has now been in operation for a few months and is working without a problem. The final Assembly and Electrical drawings can be seen here. Click on the link provided to view the drawing (Final Drawing)
Recently we have had another request for a Master/Slave scenario, where by the system had a requirement for two friction stay put joysticks which were to control one RA2 amplifier. However, we once again would have to revise the electronic design since we have discovered a problem where by the slave joystick, being a friction unit, could cause the following situation.
If, for some reason, the slave joystick is left in an active position and they begin to operate the master joystick, the master joystick takes command. This is ok, but when the master joystick is returned to the center position then the signal will return straight to the position that the slave joystick was left in.
We are currently working on a design that will use a logic that determines the desired signal by ensuring that the joystick is returned to the centre position after the use of it’s function is completed. The function will ensure that the joystick is returned to it’s neutral position before it will allow the use of the other joystick.