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• Air Bearing Spindle Units

  4.1 Description

  For manufacturing equipment of semiconductors and IT devices, it is important to maintain high accuracy flatness of wafers in the grinding process. Therefore, high runout accuracy is required for spindles used in such a process. Especially, NRRO (Non-Repeatable Runout) is required among rotational accuracy. To meet this requirement, we have newly developed air bearings that use porous graphite and obtained high accuracy NRRO.

  4.2 Features

  • （1）Includes air bearings with porous throttling,these spindle units have high rigidity when compared to other types that utilize bearings with orifice throttling, spontaneous throttling, etc.
  • （2）Reusable after slight contact since adhesion does not occur in contact with the rotating axis because of the self-lubricity of graphite.
  • （3）High rotational accuracy: NRRO (Non-Repeatable Runout) 0.05 μm or less
  • （4）Energy saving effect with air consumption minimized to 40 NL/min or less.

  4.3 Principle of Air Bearing

  As shown in Fig. 4.1, an air bearing consists of the rotating main axis and a ring or flat plate made of porous graphite to support rotation. Its performance depends on the gap amount between them and the air pressure applied there.

  ■Fig. 4.1 Principle of Air Bearing

  

  4.4 Characteristics of Radial Bearings

  （1）Basic load capacity
  The basic load capacity is represented as in the following formula, using the size of the radial bearing attached to the spindle and the supplied air pressure.
  Base load capacity = (Bearing internal diameter) x (Bearing width) x (Average pressure)
  Average pressure = Supplied air pressure / 2

  （2）Radial rigidity
  The radial rigidity is obtained by dividing the basic load capacity by the gap amount of the bearing as shown in the following formula.
  Radial rigidity = Basic load capacity/radial gap (radius)1

  （3）Example calculation
  With bearing internal diameter 70 mm,bearing width 70 mm, bearing gap 0.009 mm and supplied air pressure 0.5 MPa
  Base load capacity = 1,225 N
  Radial rigidity = 136 N/μm

  4.5 Characteristics of Axial Bearing

  （1）Basic load capacity
  The basic load capacity is represented in the following formula, using the size of the axial bearing attached to the spindle and the supplied air pressure. Basic load capacity = ((Bearing outer diameter)2－(Bearing internal diameter)2) ／ 4 × π ×（Average pressure）1

  （2）Axial rigidity
  The axial rigidity is obtained by dividing the basic load capacity by the gap amount of the bearing as shown in the following formula. Axial rigidity = Basic load capacity / Axial gap (one side)

  （3）Example calculation
  With bearing external diameter 145 mm, bearing internal diameter 75 mm, bearing gap 0.009 mm and supplied air pressure 0.5 MPa Base load capacity = 3,023 N Axial rigidity = 330 N/μm

  4.6 Structure

  

  4.7 Main Dimensions and Accuracy

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Model	Main dimensions（ｍｍ）				Rigidity（Ｎ/μｍ）		Rount（μｍ）
  	Ｄ	ｄ１	ｄ２	Ｌ	Ａ	Ｂ	Ｃ	Ｄ
  ASP90	190	90	80	521	90	300	≦2	≦2
  ASP70-1	170	70	42	466	50	350	≦2	≦2

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Model	Motor	Driver
  ASP90	Three phase AC	Commercial inverter
  ASP70-1	Three phase AC	Commercial inverter

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