Overview

This technical document from Johannes Hübner GmbH provides detailed guidance on the selection, mounting, and adjustment of torque bracket arms for hollow shaft incremental encoders of the FGH series (types 4, 6, 8, 14, 20). It focuses on ensuring high mounting precision to minimize measurement errors caused by shaft misalignments and mechanical tolerances.

1. Mounting Accuracy and Error Sources

The document identifies three main sources of mounting errors affecting the encoder's rotational accuracy:

• Radial eccentricity of the drive shaft (α1): The concentricity tolerance of the drive shaft or adapter shaft must be less than 0.04 mm (±0.02 mm). Adapter shafts can be adjusted using ball-thrust screws and aligned with a dial gauge.
• Radial eccentricity due to fitting tolerance (α2): Fits must comply with ISO 286/DIN 7145 standards. The encoder bore is H7, with recommended shaft fits of g6 for standard precision and h5 for higher precision. Shaft diameters should be manufactured slightly undersized (-0.005 to -0.015 mm) relative to the encoder bore for optimal fit.
• Axial motion of the drive shaft (α3): Axial shaft movements can cause angular errors, which are reduced by longer torque bracket lever arms. The total angular misalignment (αF = α1 + α2 + α3) must be significantly less than one quarter of the encoder's increment angle to avoid signal distortion.

2. Error Summation and Selection Criteria

The total misalignment angle αF is the sum of the three error components and represents the maximum rotational oscillation of the encoder housing. The document provides a selection table correlating pulse rate, increment angle, and lever arm length to allowable misalignment angles (αJ). The key requirement is:

αF < αJ (one quarter of the increment angle)

Users are instructed to:

1. Determine αJ from the pulse rate using the provided diagram.
2. Calculate αF based on measured or estimated shaft eccentricities and axial motion.
3. Select the torque bracket lever arm length that ensures αF < αJ.

3. Torque Bracket Lever Arm Lengths and Dimensions

The document lists standard and special lever arm lengths (B and L) for different FGH encoder types and versions (insulated short, insulated long). Dimensions and drawings are referenced for each type, with options for custom lengths on request.

4. Mounting Instructions for Torque Bracket Link Heads

Key points include:

• High-performance link heads are maintenance-free but should be checked 1-2 times per year for free rotation and treated with Teflon spray or light oil.
• For harsh environments (open-cast mining, marine, corrosive), stainless steel link heads are recommended (extra cost).
• Link heads must not be contaminated with paint.
• Proper mounting ensures the link rod rotates freely without distortion to avoid excessive bearing loads and premature failure.

5. Accessories and Components

The document details accessories such as base plates, flange plates, spacer rings, self-locking nuts, and screws made from fiberglass-reinforced plastic for insulated torque brackets. Spacer rings are critical for maintaining the correct swivel range.

6. Mounting Examples and Best Practices

Examples illustrate the ideal mounting angle between the bracket arm and link rod (90°). Deviations reduce the effective lever arm length and increase angular errors. The document also references specialized tools like detaching devices and covers with gaskets for assembly and disassembly.

7. Detailed Assembly Components

Exploded views and parts lists are provided for insulated torque brackets of various diameters (Ø8, Ø12, Ø14), including screws, spacer rings, link rods with link heads, base plates, and locking nuts. Specific DIN standards for fasteners are cited.

Critical Information Summary

• Maintain drive shaft concentricity < 0.04 mm to minimize α1 error.
• Use recommended fits (H7 bore, g6 or h5 shaft) to control α2 error.
• Minimize axial shaft motion or compensate with longer lever arms to reduce α3 error.
• Sum of errors αF must be less than one quarter of the encoder increment angle (αJ) to ensure signal quality.
• Regular maintenance of link heads is essential for longevity.
• Use appropriate accessories and follow mounting instructions precisely.

This document is essential for engineers and technicians installing FGH hollow shaft encoders with torque brackets to achieve optimal measurement accuracy and mechanical reliability.