Self – adjusted magnetic systems
Magnetic devices provide simple and effective methods for ferro-magnetic objects manipulating and transporting in robotics.
One of the advantages of such magnets is a possibility to combine censoring and power functions in one device, so that it can become self-adjusted.
The paper is focused on simple self-adjusted magnetic system for clamping, manipulating and conveying devices, based on monitoring over magnetic circuit “magnet-object”.
Significant breakthrough can be achieved in robotics for ferromagnetic objects by using magnetic lifters, manipulators, conveyors, etc. with self adjusted characteristics.
Self-adjusted magnet (SAM) is based upon monitoring over the magnetic circuit “magnet-object”, (Fig.1):
Fig.1. Generalized flow –chart of SAM control:
- Process control unit
- Magnet control unit
- Ferromagnetic object
- Magnetic circuit monitoring unit
Magnetic circuit monitoring (MCM) unit constantly measures here the changing circuit parameters, determined by the object situation and characteristics.
These parameters can be divided into three main categories: magnetic electric and time
Control over magnetic parameters can be realized by means of magnetic transducers built into magnetic circuit and monitoring magnetic flux changes in different parts of this circuit.
The author have shown that in many cases the most informative are measuring in the leakage circuits, where the linear changes of circuit flux can provide substational information on the main magnetic circuit parameters.
The magnetic state of the device magnetic circuit affects inductivity of the power unit windings provided the resistance is fixed.
Such measurements can be realized any differential circuit while switching the device on and off.
Another way of using electrical parameters in MCM is feeding the electromagnet with mixed-direct and alternating currents.
Direct current realizes here power functions, alternating current censoring.
Monitoring changes in alternating component of the electromagnet current allows to sensor the device inductivity, caused by manipulating object.
MCM units, based on time parameter also realize their measurements in electrical circuits. In practice there is often sufficient just to count the time it takes the electromagnet current to reach the specified value while the supply voltage changes.
HOW TO CHOOSE THE BEST MCM METHOD
It was shown that MCM – the heart of SAM, can be based on different monitoring principles. The choice here depends on the SAM magnetic system type and SAM application.
For all magnetic devices with permanent magnets the only way is monitoring magnetic parameters of the magnetic circuit. Which parameter to measure and in what part of the circuit depends on the type of permanent magnet used in the system.
For all ferrite, NdFeB and other sintered magnets with high magnetic resistance, the best is censoring the leakage flux.
For the systems with cast magnets the working magnetic flux gives MCM the best information.
In electromagnetic devices MCM is usually based on monitoring electrical or time parameters. The advantage here is a possibility to concentrate all measurements and control operations in the device control unit, often far away from the device.
What electrical or time parameter to monitor depends on the electromagnet application.
For clamping, holding and manipulating electromagnets first information about the object can be received while switching it on. In most cases MCM can be based here on the time parameters, which allows the simple and reliable realization.
At the same time, during the object manipulation the alternating current component of the device current can give the information to MCM.
When the object is moving according to the electromagnet, i.e. in transportation or orientation systems, the best is mostly to monitor the device current changes.
For electro permanent devices, combining permanent magnets and electromagnets in one circuit, both magnetic and electrical parameters can be used in MCM.
While switching electro permanent device on, all its magnets have to be magnetized. Due to the high magnetizing energy no electrical measurements can be made during this process, so that only magnetic parameters can be censored.
At the same time, during electro permanent device operation, its total electromagnetic system can be used or electrical MCM.
SOME EXPERIMENTAL RESULTS
On Fig.2 the leakage magnetic flux changes are shown between main poles of the permanent magnet used for steel plates lifting and manipulating.
The changes were measured wit different steel plate thickness and situation according to the magnet.
The information here can be also obtained on the object material.
On Fig.3 the alternating component change of the main current is shown for electromagnetic robot hand while approaching a ferromagnetic object and when the object covers different parts of the magnet-working surface.
The same way magnet circuit parameters changes can be measured while transporting, censoring and orienting ferromagnetic object.
HOW TO USE SAM IN ROBOTIC SYSTEM
SAM guarantees first of all safety and reliability of different technological and manipulating operations.
It can constantly inform the system control about the object situation, its unsafe movements and positions, immediately reacting to support the process.
The information from SAM can be used to change the manipulating speed while approaching the object, to change the holding or transportation force according to the process needs, control loading and unloading operations.
Besides, SAM can realize quick and deep object magnetization and demagnetization eliminating the remanence on the object surface.
In practice MCM unit can be universal for every SAM type, allowing to be teached and programmed for concrete application.
Self-adjusted magnetic holders, lifters, manipulators, conveyors and orientators, based upon monitoring over magnetic circuit “magnet – ferromagnetic object “ can adapt their operation to the position, form and situation of the object.
Smart magnet with comparatively simple means can monitor and inform the process control about the distance to the object, unsafe situations, loading possibilities, object material, etc., increasing reliability and productivity of the robotic system.