Joystick control for the future
Original article date: November 1999
Alan Quinn’s three-yearly defection to PRW Magazine to help judge its product design awards yielded this device from Ultronics – a software driven programmable electronic hydraulic proportional valve. Quite a mouthful, but a clear winner nonetheless.
It’s often predicted that on tomorrow’s truck there will be a joystick with which the driver has all functions – except steering – comfortably and naturally within the reach of one hand. This Centuri joystick from Ultronics is designed for off-road vehicles and may be typical of the controls to be seen on forklift trucks of the future.
Ultronics is a company specialising in the design, development and manufacture of software-controlled electronic-hydraulic products for the off-highway and industrial markets. It has developed a software-driven programmable proportional valve, and to drive this system, a joystick controller has been designed for construction and materials handling machines.
Many of today’s joysticks rely upon conductive technology, using contacting switches and potentiometers which have inherent wear problems and are susceptible to EMC and RF interference. External gaiters normally used for sealing also have inherent problems and are prone to damage in demanding environments.
Centuri incorporates a non-contacting optical system for both proportional control and switching, thereby eliminating the critical wearing parts. A hard-wearing armadillo ball and socket is sealed with a wiper ring to prevent ingress of contamination. Sealing to IP67 is achieved by an internal plasticised PVC gaiter that is protected from physical damage.
Control outputs are generated by an on-board Texas Instruments digital signal processor which can be programmed to provide specific functions. A utility is available to allow output parameters to be programmed to suit the application.
High current outputs can be catered for by an additional power amplifier which is specifically designed to interface with the joystick for direct drive of solenoids and other devices.
Standard joysticks can be supplied with proportional X and Y axis and with options for two other proportional axes controlled by roller modules. Single function on/off switches are also available.
If only two axes are proportional, then up to five switches are available for other functions. Being digital, it is possible to program a range of customer-specified output control options (eg dual or variable gain, dead band, etc.).
The outputs can be configured as either digital (Canbus or PWM) or analogue, thereby covering the majority of the requirements of OEMs. Operator demand is transmitted from the joystick controller via Canbus over a two-wire serial network. Signals are converted by the pilot stage microelectronics, which move the actuator pilot spools to direct pilot pressure signals to the independent metering spools, thus allowing flow to the load actuator. Sensor outputs are monitored continually to ensure accurate closed loop control.
Infinite options
Unlike conventional spool valves, inputs to either side of the load actuator can be varied independently. As a result, by using the closed loop flow and pressure control, an infinite number of vehicle control options are feasible.
Pilot valves are available without sensors for simpler open loop operation for those functions which do not require as precise control.
Each system has a conditioning valve that uses a similar pilot valve incorporating a closed loop system pressure regulator, pilot pressure regulator and system unloader.
The Ultronics Centuri joystick provides an integral fault monitoring system that limits the output voltage to between 10 and 90% of the supply voltage. If the on-board electronics detects a signal outside this range, outputs will immediately return to neutral. To prevent accidental operation, a dead man’s button can also be incorporated in the joystick.
For additional security, an infra red code hopping security system is available to isolate and immobilise the machine’s hydraulic functions until the joystick is activated. Should the machine be started by unauthorised or untrained personnel, no functions controlled by the joystick can be operated.
The power stage comprises a monobloc TS16 sectional valve with twin spools in each section. An electronic pilot valve drives each section. Aerospace grade materials have been used to maximise strength and meet the specifications laid down by the construction and materials handling industries.
- Ultronics
November 1999