Sliding Resistance of Ball Screw

This section describes the calculation method of sliding resistance with ball screw.

Friction torque by external load

• T_p : Friction torque by external load (Nm)

• Fa : Shaft direction load (N)

  Fa = F + mW

• F : External load (N)
• W : Workpiece weight + Table weight (N)
• m : Friction coefficient of slide surface (0.003 - 0.004)
• l : Lead (m)

• η : Effectiveness (0.9) ･･･ Ball screw

                (1.0) ･･･ LM guide

Friction torque by pre-load

• T_D : Friction torque by pre-load (Nm)
• Fao : re-load　(5% of Ca) (N)
• l : Lead (N)
• k : Internal friction coefficient of pre-load nut (0.1 - 0.3)
• Ca : Basic load rating (N)

Motor rated torque (T_R)

Refer to motor catalog.

Evaluation

• T_P : Friction torque by external load (Nm)
• T_D : Friction torque by pre-load (Nm)
• T_R : Motor rated torque (Nm)
• N₁ : The number of gear A teeth
• N₂ : The number of gear B teeth

Others

It is recommended to use the grinding ball screw. Rolling ball screw has so large backlash that it may not move properly.