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Super precision bearings

Bearings for combined loads

General features

Design variants

Bearings for combined loads are available as:

  • axial/radial bearings ➤ Figure
  • axial angular contact ball bearings ➤ Figure
  • axial/radial bearings with incremental angular measuring system, with pitch-coded reference marks ➤ Figure
  • axial/radial bearings with absolute value angular measuring system ➤ Figure 

Axial/radial bearings, axial angular contact ball bearings

Axial/radial bearings YRT, YRTC and YRTS and axial angular contact ball bearings ZKLDF are ready-to-fit high precision bearings for high precision applications with combined loads. They can support radial loads, axial loads from both sides and tilting moments without clearance and are particularly suitable for bearing arrangements with high requirements for running accuracy.

Simple mounting due to fixing holes

Due to the fixing holes in the bearing rings, mounting of the units is very simple. After mounting, the bearings are radially and axially preloaded. The mounting dimensions of all series are identical.

Axial/radial bearings YRT, YRTC and YRTS

Axial/radial bearings are double direction axial bearings for screw mounting, with a radial guidance bearing. These ready-to-fit, greased units are very rigid, have high load carrying capacity and run with particularly high accuracy. They can support radial forces, axial forces from both directions and tilting moments free from clearance. The bearings are available in several series ➤ Figure.

Axial/radial bearings

Fr =  radial load

Fa =  axial load

M =  tilting moment

 
For standard applications (YRT, YRTC)

 
For high speeds (YRTS)


YRT and YRTC suitable for low speeds and small operating durations

For standard applications with low speeds and small operating durations, such as indexing tables and swivel type milling heads, the most suitable bearings are series YRT and YRTC.

YRTS suitable for high speeds with low frictional torque

For the bearing arrangements of direct drive axes, there is the series YRTS. Due to their high limiting speeds and very low, uniform frictional torque across the whole speed range, these bearings are particularly suitable for combination with torque motors.

For higher running accuracy requirements, both series are also available with restricted axial and radial runout.

Axial angular contact ball bearings ZKLDF

Suitable for high speeds and long operating durations

Axial angular contact ball bearings ZKLDF are highly suitable for high speed applications with long operating duration ➤ Figure. They are characterised by high tilting rigidity, low friction and low lubricant consumption.

Axial angular contact ball bearing ZKLDF

Fr =  radial load

Fa =  axial load

M =  tilting moment


Preferred areas of use

Axial angular contact ball bearings are particularly suitable for precision applications involving combined loads. Their preferred areas of use are bearing arrangements in rotary tables with a main spindle function, for example in combined milling and turning, as well as in milling, grinding and honing heads and in measurement and testing equipment.

Axial/radial bearings with incremental angular measuring system

Features

Axial/radial bearings with an incremental angular measuring system and pitch-coded reference marks comprise an axial/radial bearing YRTM or YRTSM, each with a dimensional scale, an SRM electronic measuring system and signal leads SRMC ➤ Figure. The electronic measuring system SRM comprises two measuring heads, two stacks of shims and an electronic evaluation system ➤ Figure. The signal leads for connecting the measuring heads to the electronic evaluation system can be ordered individually in various designs.

Equivalent in mechanical terms to series YRT and YRTS

Bearings of series YRTM or YRTSM correspond in mechanical terms to axial/radial bearings YRT or YRTS, but are additionally fitted with a magnetic dimensional scale. The measuring system can measure angles to an accuracy of a few angular seconds by non-contact, magneto-resistive means.

Axial/radial bearing with incremental angular measuring system

 
Measuring heads with shims

 
Connection cable SRMC

 
Electronic evaluation system


Advantages of the angular measuring system

The measuring system:

  • allows, due to the rigid connection to the adjacent construction, very good control characteristics (control stability and dynamics) and is therefore particularly suitable for axes with torque motor drive
  • offers a high maximum measuring speed of up to 16,5 m/s
  • operates by non-contact means and is therefore not subject to wear
  • carries out measurement irrespective of tilting and position
  • has automatically self-adjusting electronics
  • has a self-centring function
  • is unaffected by lubricants
  • is easy to fit, the measuring heads are easily adjustable, there is no need for alignment of the bearing and a separate measuring system
  • requires no additional parts
    • the dimensional scale and measuring heads are integrated in the bearings and adjacent construction respectively
    • the resulting space saved can be used for the machining area of the machine 
  • does not give any problems relating to supply cables. The cables can be laid within the adjacent construction directly through the large bearing bore
  • gives savings on components, overall design envelope and costs due to the compact, integrated design requiring fewer components

Axial/radial bearings with absolute value angular measuring system

Equivalent in mechanical terms to series YRT and YRTS

Axial/radial bearings with absolute value angular measuring system YRTMA and YRTSMA correspond in mechanical terms to series YRT and YRTS, but are additionally fitted with an absolute value angular measuring system ➤ Figure.

Axial/radial bearing with absolute value angular measuring system


High system measuring accuracy of angular measuring systems integrated in the bearing

The ideal location for mounting a measuring system is directly in the bearing arrangement, which means that higher system accuracies can be achieved with measuring systems integrated in the bearing than with measuring systems that are attached to the axis a significant distance from the relevant bearing arrangement. The very precise radial runout of the precision rotary axis bearing YRT(S)MA is utilised here.

The absolute angular measuring system integrated directly in the bearing offers considerable advantages:

  • an absolute interface, dispensing with the need for reference travel
  • a hollow shaft design, freeing up the centre of the machine for other components
  • the facility for highly dynamic and precise control loops
  • savings in terms of design envelope
  • simplifications in design and mounting
  • resistance to environmental influences, lubricants and cooling lubricants

Inductive measurement method ABSYS (AMO)

The inductive measurement method ABSYS (AMO) is based on contact-free scanning of a structured dimensional scale that is applied directly as a measurement ring to the bearing inner ring ➤ Figure. The irregular structure with absolute coding is captured on a bitwise inductive basis by a coil arrangement that is integrated in the measuring head.

The binary value obtained, which occurs only once per angular position within the entire measurement range, is converted into an absolute angular value by a microcontroller using a conversion table.

The electronic evaluation system is integrated in the measuring head, so the system can be connected directly to the controller. The measuring head is configured such that no adjustment of the measurement gap is required and the rolling bearing chamber is protected against the egress and ingress of lubricants and other media. Other measuring head designs are available by agreement.

Absolute value angular measuring system

 
Measuring head

 
Measurement ring

 
Inner ring of axial/radial bearing