-Casting Robot-

Introduction


Casting process is one of the metal working processes in which pouring molten metal which is melted by heat more than 1300 K, to a sand mold to form metal target shapes. In the pouring process of casting, a skilled worker pours molten metal from a ladle to the mold. However, production lines are inhospitable environments for workers because of the high heat and powder dust. Also, it is too difficult to achieve a high accuracy pouring that handling of molten metal is difficult by hand work.

Automatic Pouring Robot
To solve these problems, we have studied about transferring liquid with non-sloshing and pouring molten metal to proper position with high accuracy flow rate. We design controller and systems based on physical principles and evaluate efficiency of them by numerical simulations and experiments using water.

Sloshing Suppression Control

If sloshing is caused while pouring molten metal, quality of product or molten metal decreases by involving slag (oxide). It also becomes that molten metal is poured into non-exact position since falling trajectory of molten metal fluctuates by sloshing.
We have studied motion control and transfer systems not to cause sloshing in ladle without level sensors.

■Sloshing suppression control using pendulum model

The sloshing phenomena has periodicity and natural frequency same as a pendulum. So we proposed a "pendulum model" that approximates sloshing phenomena to pendulum vibration, and considered sloshing suppression applying conventional approach of vibration suppression control. The movies below show a example of liquid container transfer applying notch filter to remove natural frequency element from input voltages.

(Click to play the movie)

with suppression control

■Suppression of higher order vibration with BEM model


Sloshing Model with Boundry Element Method
Transfer system becomes able to suppress high-order mode vibration that can't be expressed on pendulum model, modeling sloshing phenomena by boundary element method (BEM). We can also achieve transferring container not to tilt liquid surface, control transfer and tilting motion simultaneously. It is showed that vibration of liquid level is suppressed within 2mm on equipment in laboratory by estimating sloshing and deriving acceleration of transfer and tilting.

with only transfer (upper figure)
with tranfer and tilting motion (lower figure)

Flow Rate Control


One of approach for flow rate control memory tilting motions of skilled workers and play back them. This approach needs recordation of tilting pattern with variety of ladle and mold. In our group, flow rate model is constructed based on physical principle and we derive proper motor input from inverse model of it to achieve flow rate control.
It is achieved that an error of fill up volume has been suppressed less than 3% by applying this model.

Falling Position Control


If flow rate control is realized with high accuracy, we can estimate flow velocity and falling trajectory of outflow liquid from ladle. Falling behavior of outflow liquid is considered same as free fall motion of rigid body, so falling position on horizontal direction is derived from height of pouring mouth. Falling position control is achieved by transferring ladle back and forth depending on estimated falling position.

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