Smart systems bring benefits to industrial applications
The number and sophistication of 'smart' industrial motion control systems is rising all the time. What is more, these technologies, which incorporate a range of electronic control systems within them, are increasingly proving capable of replacing more traditional technologies.
One example of this can be seen in the smart electromechanical numerical joining systems from Kistler, include a piezoelectric force sensor and a rotary encoder to measure and control position. The actuator is linked to a servo controller and a programme/monitor unit.
This approach offers a number of benefits, making it possible to specify a series of positions and speeds, to define clearly the fit process. A position repeatability of <0.01mm is possible. A fit programme consisting of a series positions and speeds can be entered into the control electronics, while for some operations force feedback can be used. This control programme can easily be adjusted for different parts and materials: the degree of control offered by electrical systems greatly exceeding that offered by hydraulic or pneumatic systems.
And, as Nick Gittins, Kistler's sales manager, makes clear, it is in applications where accurate positioning is required that the sort of control offered by 'smart systems' really comes into its own. He says: "If you've got a requirement where you need to closely control position, then this is an ideal tool. With things like drug delivery devices, for instance, where the plastic means the forces are quite low, but the quality threshold is high because these things need to work, you need careful control or both you and the end user in trouble."
This sort of application involves the interference fit of parts. This is where a part is pushed into a recess, which is slightly undersized, causing interference. The fit is made possible by the material elasticity, which gives rise to a compressive force between the part and the recess. The join is maintained by the friction, which is a function of this compressive force.
Hydraulic actuation is usually used for interference fit operations. Occasionally, pneumatic or mechanical cams are used for low forces. However, in recent years industry has been switching to this new generation of electrical actuators.
For many years, interference fit processes have been monitored with force and displacement sensors, providing a quality assessment of all fit operations. Sensors are linked to an electronic monitor, to generate an XY plot for each fit operation. The monitor can then apply limits to the plot and, for example, reject a fit with an inadequate interference force at a specified position.
Electromechanical NC joining systems are, claims Gittins, taking over from the familiar hydraulic presses and conventional joining modules, not least because the piezoelectric force sensor, rotary encoder to measure and control position – plus the link to a servo controller and a programme/monitor unit – offer much higher levels of positional accuracy.
Another instance where 'smart' equipment is making a big difference is in damping, where EasyERF Intelligent Damping from German manufacturer Bansbach, offers electronically adjustable dampers with reaction times measured in milliseconds.
Combining smart Proportional Integral Derivative (PID) systems and the latest in electrorheological fluid (ERF) technology, this autonomous system continuously monitors and modifies resistance forces within the damper. Achievable by digitally managing an electronic input signal to change the ERF fluid's viscosity within the damper, this unique system offers instantaneous control of dynamic damping requirements with infinite adjustment possibilities.
Smart PID Systems consist of at least one adjustable easyERF damping cylinder and one amplifier with an integrated controller. In its basic form, this 'open loop' system involves manually managing the controller to modify the damping properties. For autonomous 'closed loop' systems, control measurement elements such as sensors can easily be integrated into the system to measure parameters such as acceleration, displacement and weight.
Highly energy-efficient with low power consumption (24 volt DC), damping can be adjusted using a variety of digital controls which can include 0 – 4V analogue, a standard PWM or, with a 24 volt DC SPS. Silent in operation with no 'laminar flow' or 'whistling' noises, the system has no movable parts to ensure maintenance free operation.
With a wide adjustable range of forces between 100N and 2500N through strokes ranging from 25mm to a maximum of 125mm, accurate positioning is achievable to within 0.1 of a millimetre.
This range of intelligent dampers was initially developed for active suspension systems within the top marque automotive sector it was instantly recognised that this technology had a much broader scope of possibilities, particularly within industrial sectors involving machine suspensions, precise motion control actuators or self adaptive end-of-stroke damping elements.
Electrorheological fluids (ERF) belong to the group of Bingham materials and are dispersions consisting of oil (mineral or silicon oil) and solid polymer particles. The viscosity of such fluids can be modified by the application of an electrical charge. The greater the charge, the greater the viscosity, even to the point of solidifying liquids. Fully reversible, this effect of changing the fluid's properties is achievable within a few milliseconds. The ERF fluid remains unaffected by the number of times it's viscosity changes and Bansbach easyERF dampers have been tested to over half a million cycles with no signs of deterioration.
The system consists of a piston with a defined gap, known as the Annular Gap between housing and piston and two chambers filled with silicon-based electrorheological fluid. With no electrical charge applied, the fluid flows through an annular valve as in a standard damper. The inherent resistance is caused by the hydraulic drag coefficient of the laminar fluid flow. On application of an electrical charge, the viscosity of the fluid increases, thus choking the annular valve, resulting in an increase in the resistance force of the damper. A special feature of a smart PID system is that by increasing the electrical field to it's maximum the ERF solidifies resulting in a total blocking of mass movements, achieving 'zero velocity' or 'clamping'.
The system also offers continuous force control, as there is a wide range between soft and hard damping characteristics, which can be adjusted at any point along the stroke.Equally, smart PID Systems need only a few milliseconds to increase the damping force, so it is possible to control processes with high frequencies, while at zero velocity, it is possible to clamp or block the ER damping cylinder by supplying an electrical field, similar to that of a friction clutch, thereby eliminating the need for other clamp elements.
This electrorheological technology also offers new possibilities for the development of mechatronic systems. By incorporating Smart PID Systems it is possible to dramatically improve performance efficiencies of a diverse range of applications which could include, automated handling equipment such as conveyors, crushers, dryers or centrifuges; production machinery involved in drilling, forming, or milling; or even within the medical equipment arena such as exercise machines typically used in resistance training for heart attack patients or victims of congenital or acquired limb loss.
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