Ballscrews ( complete program ) - HIWIN - #39

When the temperature rises in the ballscrew, the effect of thermal stress will elongate the screw spindle. It can make the spindle length unstable.0

The elongating relationship can be calculated according to M41. This elongation can be compensated via the pretension force. For the purpose of pretension, there is a negative T value indicated in the design drawing to compensate the pretension value.

Since a large pretension force will cause the burn down of the supporting bearing, HIWIN recommends using pretension when the temperature rise is below 5°C. Also, if the diameter of the screw spindle is greater than 50 mm, it is not suitable for pretension. A large spindle diameter requires a high pretension force, causing burn down of the supporting bearing.

HIWIN recommends a T compensation value of about 3°, (about -0.02~0.03 for each 1000 mm screw spindle).

Since different applications require different T values, please contact HIWIN engineer.

The pretension force is calculated as :

P_f = K_s x AL

K_s : Stiffness of screw spindle (kgf/um) Pf: Pretension force (kgf) AL : Pretension valus (um)

Table 4.12 : Inspection and replenishment of Lubricant

hollow screw spindle

M

Nut

Pressure switch

condenser rPt

M

evaparator

Hi

X axis

Ballscrew thermal recorder

Oil inlet

M

te

Z axis

refrigerator

Oil tank

thermal

Y axis

A4

Fig 4.33 High accuracy machine tools with hollow ballscrew lubrication