The HydroMaxTM

Modular Self-Compensating Hydrostatic Linear Bearing

(U.S. Patents 5,104,237, 5,484,208, Other Patents Pending)

 

 

 

 

The HydroMaxTM Modular Hydrostatic Bearing System

The HydroMaxTM bearing is a patent pending hydrostatic linear guide which is currently being developed by Aesop, Inc. and the Massachusetts Institute of Technology. The purpose of the HydroMaxTM is to meet the needs of the most demanding machine tool applications, while providing the economy and ease of "bolt-for-bolt" compatibility with standard rolling element linear guides.

The HydroMaxTM bearing consists of a modular carriage which rides on a thin fluid layer present between the scientifically contoured bearing surfaces of the carriage and the rail. During operation, hydraulic fluid pressurized to 1,200 psi enters the fluid manifold, where it is distributed to the self compensating hydrostatic bearing pads, which provide bearing stiffness and load carrying capability. Fluid exits out of the bearing gap into the atmosphere, where it collects into drainage gutters under the carriage and is ultimately recirculated through a filter and pump system back to the carriage.

The key innovative feature of the HydroMaxTM bearing is a pair of self compensating hydrostatic bearing surfaces which wrap around the curvilinear contours on each side of a profile rail (Patents Pending). In a conventional hydrostatic bearing system, four planar pad surfaces, separated by drainage grooves, surround a box rail. Compared to a conventional design with the same rail size and load carrying capacity, the Wrap-AroundTM design cuts the fluid flow rate and pump power required to operate the bearing by 50% to 70%. The substantial reduction in flow rate greatly reduces heat transferred to the machine tool, and reduces the size and cost of the fluid system. The Wrap-AroundTM design is also less costly to manufacture than a box way hydrostatic system of the same size, due to its simplicity.

 

The Performance Benefits of the HydroMaxTM Bearing

The following table shows the projected performance of a size 45 HydroMaxTM bearing verses a high end rolling element linear guide currently on the market.

 

The HydroMaxTM bearing Vs. a     Size 45, @1190 psi   Size 45    
high end rolling element bearing     HydroMaxTM Bearing   Rolling Element Bearing
      Nominal gap = 0.001 in.   Ultra Precision, 0.03 Preload
     

Compress.

Tension

Lateral

  

Compress.

Tension

Lateral
Static Load which causes permanent damage

lb

  

250,000 1

75,000

110,000

  

29,750 5,7

29,750

29,750
Dynamic Load Capacity at given Life

lb

  

2,500 2,3

2,500

6,500

  

3,000 6,7

3,000

3,000
Life

km

  

no limit

      

1,000

    
Static Stiffness

lb/min

  

3.0 3

2.7

4.6

  

5.1 7

4.7

7.1
Dynamic Stiffness at Resonance

lb/min

  

2.03,4

1.8

3.0

  

0.8 8

0.8

1.1
Q (Damping Factor)

-

  

1.5 4

      

6.2 8

    
Maximum Speed

m/s

  

no limit

      

2 7

    
Maximum Acceleration

m/s2

  

no limit

      

50 7

    
Static Friction

lb

  

none

      

3.2 7

    
Motion Resolution

min

  

infinite

      

40 10

    
Friction @ 0.5 m/s

lb

  

4.2 3

      

9.4 7

    
Friction Power @ 0.5 m/s

W

  

9.4 3

      

21.0 7

    
Straightness (over 15.5 inches travel) 9

min

  

20 4

      

45 8

    
Straightness Repeatability

min

  

8 4

      

17 8

    
Hydraulic Oil Flow (m=76 cSt @ 90 F)

gpm

  

0.2 3

  
Pumping Power required

W

  

100 3

            

 

 

This table illustrates the technical advantages and tradeoffs associated with the HydroMaxTM bearing. All of the outstanding features shown, such as high static load capacity, high dynamic stiffness at resonance, and infinite motion resolution, are direct benefits of the hydrostatic fluid layer, which acts like an energy dissipating cushion while also providing no static friction. Rolling elements, on the other hand, are fundamentally limited in these performance categories due to the physical limitations of Hertzian contact between rolling elements and races.

The following table lists some major features and benefits of the HydroMaxTM bearing.

 

HydroMaxTM Feature Benefits for Various Applications
Very high "crash" resistance Greatly reduces the chance that a crash will result in expensive downtime for bearing repair.
Potentially infinite bearing life If fluid filter is replaced regularly, cost of rebuilding linear ways can be eliminated.
High damping Reduces problematic chatter, increases surface finish.
Zero static friction Reduces servo reversal error; increases motion resolution, allowing 20 min infeeds or smaller.
Low dynamic friction Reduces heat generation and hence reduces thermal errors at high speeds.
High straightness Results in straighter surfaces, more accurate parts.
Swarf particles can pass freely through bearing gap Virtually immune to the extremely destructive effects of ceramic swarf when grinding ceramic materials. Allows bearing to remain accurate over several years of operation without a rebuild.

 

 

Cost Estimates for HydroMaxTM Components

 

Estimated Carriage and Rail Costs     Fluid System Cost  
Bearing Size

35

45

55

65

   To Power 4 Carriages of any size

$3,800

Per Carriage

$570

$600

$650

$700

  To Power 8 Carriages of any size

$4,800

Per meter of rail

$770

$800

$850

$900

  To Power 12 Carriages of any size

$5,600

1 Estimates are based on an ultra precision rolling element linear guide system with similar manufacturing complexity

2 Includes DC permanent magnet motor (1 hp per 4 carriages), power supply, gear pump, 3mm high pressure filter, properly sized oil chiller with a 10 gallon tank, pressure relief value, a pressure measurement and control system, 10 foot hydraulic hose, and 15 gallons of hydraulic oil. Does not include fittings and hoses going to individual trucks, fluid gutters and drains, or a way protection system such as bellows.

 

New Possibilities for Machine Tool Manufacturers

· Offer "Check the Box" Hydrostatics to Customers Buying a New Machine

  • Linear Bearing Option: Standard Linear Guides HydroMaxTM Hydrostatic Linear Guides
    •

    · Upgrade an Entire Product Line Quickly and Inexpensively

  • With minimal additions (such as adding drainage gutters for hydraulic oil), an old product line that uses standard linear guides can be rejuvenated by equipping the machines with HydroMaxTM bearings.
    •

    · Introduce a New Ultra Performance Machine Tool Which is Very Cost Competitive

  • Design a new ultra performance high speed machining center which takes full advantage of the performance capabilities of the HydroMaxTM bearing. Promote the unique "crash" resistant, accuracy enhancing, and long bearing life features, and also the high value added to the machine tool by the HydroMaxTM technology, which translates directly into a great value for the customer.

    • · Replace Costly Hand Scraped Way Systems

  • In an effort to reduce assembly time and costs, countless machine tool manufacturers have spent thousands of R&D dollars trying to make rolling element guides work for them, only to give up and go back to using their old labor intensive, costly custom way systems (such as sliding and hydrodynamic systems which require hand scraping). For many of these companies, the HydroMaxTM can offer the ultra high performance they require while also providing them with much of the savings that they are looking for.
    •

    New Possibilities for Machine Tool Users

     

    · Retrofit a Machine to Bring it to a New Level of Accuracy

  • During a rebuild, a machine that uses standard linear guides can be economically upgraded to HydroMaxTM bearings. For a modest investment, the machine can then can perform at a new level of accuracy.
    •

    · Retrofit a Machine to Greatly Increase Bearing Life in Abrasive Environments

  • When grinding ceramics or other hard materials, the abrasive swarf created always gets past even the best bearing seals, and then quickly wears the surfaces of rolling elements and races. Retrofitting such a machine with HydroMaxTM bearings can eliminate this problem, since the bearing gap is large enough to allow swarf particles to pass through freely.
    •

    Market Survey for the HydroMaxTM Bearing

    We are currently gathering marketing data to assess the business potential for this product. If your company would be interested in purchasing this product if it were available on the market, please complete this form and send it to Nathan R. Kane via fax, mail, or e-mail. Thank you for your time.

     

    Type of machine to use HydroMaxTM Bearings

    Bearing Size

    # of Carriages

    Meters of Rail

    Machine Sales
    Example: 3 Axis Mill

    35

    4

    1.8

    		  
     

    45

    8

    5.8

    30

     

    For questions of a technical nature, please contact Nathan R. Kane. For questions of a business nature, please contact Professor Alexander Slocum.

     

    Nathan R. Kane
    Massachusetts Institute of Technology
    77 Massachusetts Avenue Room 3-445
    Cambridge, MA 02139
    Ph: (617) 253-1953
    Fx: (617) 258-6427
    e-mail:     nrkane@mit.edu    		   Professor Alexander Slocum
    Massachusetts Institute of Technology
    77 Massachusetts Avenue Room 3-445
    Cambridge, MA 02139
    Ph: (617) 253-0012
    Fx: (617) 258-6427
    e-mail:     slocum@mit.edu