[8]hsa pivot bearingeffect_good
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The document summarizes a study on how the process of assembling the pivot bearing affects the natural frequency of actuator arms in hard disk drives. The experiment varied the inside diameter of actuator arms and measured the installation force and natural frequencies after assembling with pivot bearings and tolerance rings. Results showed modes 4 and 5 had significantly different frequencies that correlated with installation force and bore size. Finite element modeling agreed with experimental results. In conclusion, the pivot bearing assembly process, particularly the compressive force from tolerance rings, impacts some vibration modes of the actuator arm.
![Journal of Energy and Power Engineering 7 (2013) 301-305
The Effect of Pivot Bearing Assembly Process on
Natural Frequency of Actuator Arm
Khosak Achawakorn1, 2
, Thira Jearsiripongkul1
, Sarawut Suksawat1
and Krairoek Fanchaeng3
1. Department of Mechanical Engineering, Faculty of Engineering, Thammasat University, Patumthani 12120, Thailand
2. Mechatronics Department, School of Engineering, Sripatum University, Bangkok 10900, Thailand
3. Failure Analysis and Reliability Department, Belton Industrial (Thailand), Patumthani 12120, Thailand
Received: May 07, 2012 / Accepted: August 08, 2012 / Published: February 28, 2013.
Abstract: This paper presents the study of vibration in each element of hard disk drive, especially the resonance of the actuator arm.
The resonance occurs in hard disk drive is considered as one of the quality controlled parameter. The main purpose of the research is to
investigate the relationship between the pivot bearing assembly process and the natural frequency of the actuator arm. The experiment
is designed using the information from the hard disk drive manufacturer. The selected pivot bearing assembly process parameters have
been controlled. The modal analysis of the assembled actuator arms has been done. The experiment results show the relationship of the
specific process parameters and some of the actuator arm’s modal frequency. The results also show that the affected vibration mode is
the torsion mode only.
Key words: Pivot bearing, actuator arm, tolerance ring, natural frequency.
1. Introduction
The hard disk drive manufacturers are now very
concerning of the vibration in each element of the hard
disk drive, especially, the resonance in the actuator arm.
The resonance in the actuator arm could lead to the
reliability problem that is read-write error or durability
problem that is media’s surface damaging, which effect
directly to the efficiency of the hard disk drive. To
control the natural frequency of the actuator arm,
various parameters are concerned such as the geometry
of component and material properties. The components
are made very precisely. The parameters of the
manufacturing process are strictly controlled. The very
little non-conformance parameters could lead to the
quality problems of finished goods. The assembly
method of the actuator arm is another important factor
that affects the natural frequency of the actuator arm.
Corresponding author: Khosak Achawakorn, lecturer,
research fields: industrial automation, mechanical vibration and
sensor technology. E-mail: khosak.ac@spu.ac.th.
Manufacturers invented their own designs and
techniques to assembly the actuator arm and its pivot
bearing. To keep the best precision and least vibration,
the various techniques of pivot bearing assembly
methods have been invented [1-3]. Even they have
been reduced by many methods, the natural frequency
of the components exist. The hard disk drive
manufacturers live with the natural frequency by
avoiding the use of those frequencies in their hard disk
drive. The notch filter and other techniques are applied.
To make this idea correct, every pieces of each
component supplied to the hard disk drive manufacturer
must have the invariable natural frequency.
The vibration of the head stack assembly is subjected
to the vibration of every component from the
suspension to the pivot shaft. The actuator arm and its
related parts are manufactured under the quality control
standard. The natural frequency is one of the quality
control parameter.
The pivot bearing is one component that influences
DDAVID PUBLISHING](https://image.slidesharecdn.com/8hsapivotbearingeffectgood-150321120131-conversion-gate01/85/8-hsa-pivot-bearingeffect_good-1-320.jpg)
![The Effect of Pivot Bearing Assembly Process on Natural Frequency of Actuator Arm302
the natural frequency of the head stack assembly. The
pivot bearing is studied by many researchers [4, 5]. The
pivot bearing stiffness that affect head stack assembly
vibration is presented in Ref. [6]. The simulation
technique and the other numerical techniques are also
introduced for modal analysis of the pivot bearing and
other component of the hard disk drive [7-10].
This paper presents the study of vibration in the
actuator arm. The comparison between experiment
results and simulation result show the relationship of
the pivot bearing assembly using tolerance ring in
relation to the modal frequency of the actuator arm.
2. Pivot Bearing Assembly Technique
The pivot bearing and actuator arm assembly
process is now done in two favorite methods, i.e., using
adhesive and using tolerance ring. Objective of the
both methods are to withhold the pivot bearing and the
ACA (arm coil assembly) together.
2.1 Adhesive-injection Method
This method is one of the most common processes to
withhold the pivot bearing and the ACA. The adhesive
is injected in to the space between the pivot bearing and
the ACA that is usually called glue groove. The
advantage of this method is that the adhesive withhold
the parts together without any load directly act on the
inner surface of ACA. The drawback of this method is
the material property of the glue and the flow control
during the injection.
2.2 Tolerance Ring Insertion Method
The tolerance ring is metal split ring used for
assembly the pivot bearing and the actuator arm
together. The pivot bearing and the actuator arm is
withheld by the friction at the surface of the tolerance
ring as shown in Fig. 1. The amount of friction depends
on compressive force acted by the tolerance ring. The
compressive force depends on the change of bump
height as shown in Fig. 2, which is related to the
outside diameter of the pivot bearing, inside diameter
of the actuator arm, and dimple height of the tolerance
Fig. 1 Illustrate the pivot bearing assembly using tolerance
ring.
Fig. 2 Illustrate the tolerance ring.
ring. The compressive force also directly acts on the
inner surface of the actuator arm. Then the modal
frequency of the actuator arm is theoretical shifted due
to the varying of the compressive force which is act as
pre-stress of the actuator arm.
3. Experiment
The objective of this research is to identify the
factors that affect the change of compressive force
and its effect on the modal frequency of the actuator
arm.
3.1 Assumption
The assumption of the experiment is the variation of
compressive force affects the modal frequency of the
actuator arm. The compressive force should have
relation to various parameters such as the dimension of
each element, the force feedback of the pivot bearing
insertion process.](https://image.slidesharecdn.com/8hsapivotbearingeffectgood-150321120131-conversion-gate01/85/8-hsa-pivot-bearingeffect_good-2-320.jpg)
![The Effect of Pivot Bearing Assembly Process on Natural Frequency of Actuator Arm 305
Fig. 9 The finite element model of the APFA.
Table 4 Modal frequencies (FEM).
Mode
Modal frequency of each group (kHz)
1 2 3 4 5
1 7.17 7.21 7.26 7.28 7.33
2 11.30 11.33 11.34 11.36 11.40
3 14.76 14.84 14.94 15.09 15.12
4 24.60 24.72 24.84 25.11 25.51
5 27.62 27.71 27.96 28.25 28.58
6 35.35 35.41 35.48 35.51 35.59
7 40.91 41.19 41.25 41.31 41.43
Fig. 10 Illustrate the FEM arm bending mode.
Table 5 Comparison of modal frequency result.
Mode
Modal frequency of group 3 (kHz)
% error
Experiment FEM
1 7.37 7.26 1.49
2 11.53 11.34 1.65
3 15.38 14.94 2.86
4 26.31 24.84 5.59
5 30.15 27.96 7.26
6 38.37 35.48 7.53
7 45.22 41.25 8.78
of the quality of the specimens, since there are a lot of
part in the HDD (hard disk drive) could affect the
modal frequency.
The theoretical analysis might be applied to
determine the relations of the variation of parameters to
the modal frequency.
Acknowledgments
Special thanks to I/UCRC in HDD Advanced
Manufacturing KMUTT (HDD-08-01-50 D) for
funding support, Belton Industrial (Thailand), and
DVG (Dynamics and Vibrations Group) Mechanical
Department, Thammasat University for great support.
References
[1] W.L. Prater, Hard disk drive actuator assembly with
damped tolerance ring for enhances drive performance
during structural resonance mode, United States Patent,
6480363 B1 (2002).
[2] N.E. Larson, Hard disk assembly having a pivot bearing
assembly comprising fingers bearing on a shaft, United
States Patent, 5757588 (1998).
[3] J.R. Edwards, J.M. Garbarino, Disk drive having
elastomeric interface in pivot bearing assembly, United
States Patent, 5666242 (1997).
[4] P. Ampaipipatkul, S. Sedsittichoke, S. Phopli, T. Phonpai,
T. Jearsiripongkul, Vibration analysis of pivot bearing
using LDV and identification using FEM, in: The 21st
Mechanical Engineering Network Thailand, Chonburi,
Thailand, 2007.
[5] T. Jintanawan, C.P.R. Ku, J. Zhu, Effects of thrust
hydrodynamic bearing stiffness and damping on
disk-spindle axial vibration in hard disk drives,
Microsystem Technologies 10 (2004) 338-344.
[6] L.M. Xu, N. Guo, Modal testing and finite element
modeling of subsystems in hard disk drives, Mechanical
System Signal Process 17 (2003) 747-764.
[7] J. Lue, D.W. Shu, Q.Y. Ng, R. Zambri, J.H. Lau, B.J. Shi,
On the simulation of the pivot bearing inside HDD,
Journal of Magnetism and Magnetic Materials 303 (2006)
e81-e84.
[8] F. Gao, F.F. Yap, Y. Yan, Modelling of hard disk drive for
variation analysis using a flexible multibody dynamics
formulation, IEEE Transactions on Magnetics 41 (2)
(2005) 744-749.
[9] L.M. Xu, N. Gao, Modal testing and finite element
modeling of subsystem in hard disk drive, Mech. Syst.
Signal Process. 17 (4) (2003) 747-764.
[10] K. Ryota, T. Kazuhiro, I. Kenichiro, W. Singeru, I
Takayuki, T. Kazuo, Modal analysis of HDD’s actuators,
Fujikura Tech. 31 (2002) 7-12.](https://image.slidesharecdn.com/8hsapivotbearingeffectgood-150321120131-conversion-gate01/85/8-hsa-pivot-bearingeffect_good-5-320.jpg)
[8]hsa pivot bearingeffect_good
- 1. Journal of Energy and Power Engineering 7 (2013) 301-305 The Effect of Pivot Bearing Assembly Process on Natural Frequency of Actuator Arm Khosak Achawakorn1, 2 , Thira Jearsiripongkul1 , Sarawut Suksawat1 and Krairoek Fanchaeng3 1. Department of Mechanical Engineering, Faculty of Engineering, Thammasat University, Patumthani 12120, Thailand 2. Mechatronics Department, School of Engineering, Sripatum University, Bangkok 10900, Thailand 3. Failure Analysis and Reliability Department, Belton Industrial (Thailand), Patumthani 12120, Thailand Received: May 07, 2012 / Accepted: August 08, 2012 / Published: February 28, 2013. Abstract: This paper presents the study of vibration in each element of hard disk drive, especially the resonance of the actuator arm. The resonance occurs in hard disk drive is considered as one of the quality controlled parameter. The main purpose of the research is to investigate the relationship between the pivot bearing assembly process and the natural frequency of the actuator arm. The experiment is designed using the information from the hard disk drive manufacturer. The selected pivot bearing assembly process parameters have been controlled. The modal analysis of the assembled actuator arms has been done. The experiment results show the relationship of the specific process parameters and some of the actuator arm’s modal frequency. The results also show that the affected vibration mode is the torsion mode only. Key words: Pivot bearing, actuator arm, tolerance ring, natural frequency. 1. Introduction The hard disk drive manufacturers are now very concerning of the vibration in each element of the hard disk drive, especially, the resonance in the actuator arm. The resonance in the actuator arm could lead to the reliability problem that is read-write error or durability problem that is media’s surface damaging, which effect directly to the efficiency of the hard disk drive. To control the natural frequency of the actuator arm, various parameters are concerned such as the geometry of component and material properties. The components are made very precisely. The parameters of the manufacturing process are strictly controlled. The very little non-conformance parameters could lead to the quality problems of finished goods. The assembly method of the actuator arm is another important factor that affects the natural frequency of the actuator arm. Corresponding author: Khosak Achawakorn, lecturer, research fields: industrial automation, mechanical vibration and sensor technology. E-mail: khosak.ac@spu.ac.th. Manufacturers invented their own designs and techniques to assembly the actuator arm and its pivot bearing. To keep the best precision and least vibration, the various techniques of pivot bearing assembly methods have been invented [1-3]. Even they have been reduced by many methods, the natural frequency of the components exist. The hard disk drive manufacturers live with the natural frequency by avoiding the use of those frequencies in their hard disk drive. The notch filter and other techniques are applied. To make this idea correct, every pieces of each component supplied to the hard disk drive manufacturer must have the invariable natural frequency. The vibration of the head stack assembly is subjected to the vibration of every component from the suspension to the pivot shaft. The actuator arm and its related parts are manufactured under the quality control standard. The natural frequency is one of the quality control parameter. The pivot bearing is one component that influences DDAVID PUBLISHING
- 2. The Effect of Pivot Bearing Assembly Process on Natural Frequency of Actuator Arm302 the natural frequency of the head stack assembly. The pivot bearing is studied by many researchers [4, 5]. The pivot bearing stiffness that affect head stack assembly vibration is presented in Ref. [6]. The simulation technique and the other numerical techniques are also introduced for modal analysis of the pivot bearing and other component of the hard disk drive [7-10]. This paper presents the study of vibration in the actuator arm. The comparison between experiment results and simulation result show the relationship of the pivot bearing assembly using tolerance ring in relation to the modal frequency of the actuator arm. 2. Pivot Bearing Assembly Technique The pivot bearing and actuator arm assembly process is now done in two favorite methods, i.e., using adhesive and using tolerance ring. Objective of the both methods are to withhold the pivot bearing and the ACA (arm coil assembly) together. 2.1 Adhesive-injection Method This method is one of the most common processes to withhold the pivot bearing and the ACA. The adhesive is injected in to the space between the pivot bearing and the ACA that is usually called glue groove. The advantage of this method is that the adhesive withhold the parts together without any load directly act on the inner surface of ACA. The drawback of this method is the material property of the glue and the flow control during the injection. 2.2 Tolerance Ring Insertion Method The tolerance ring is metal split ring used for assembly the pivot bearing and the actuator arm together. The pivot bearing and the actuator arm is withheld by the friction at the surface of the tolerance ring as shown in Fig. 1. The amount of friction depends on compressive force acted by the tolerance ring. The compressive force depends on the change of bump height as shown in Fig. 2, which is related to the outside diameter of the pivot bearing, inside diameter of the actuator arm, and dimple height of the tolerance Fig. 1 Illustrate the pivot bearing assembly using tolerance ring. Fig. 2 Illustrate the tolerance ring. ring. The compressive force also directly acts on the inner surface of the actuator arm. Then the modal frequency of the actuator arm is theoretical shifted due to the varying of the compressive force which is act as pre-stress of the actuator arm. 3. Experiment The objective of this research is to identify the factors that affect the change of compressive force and its effect on the modal frequency of the actuator arm. 3.1 Assumption The assumption of the experiment is the variation of compressive force affects the modal frequency of the actuator arm. The compressive force should have relation to various parameters such as the dimension of each element, the force feedback of the pivot bearing insertion process.
- 3. The Effect of Pivot Bearing Assembly Process on Natural Frequency of Actuator Arm 303 3.2 Experiment Setup To proof that the dimension of parts affect directly on the modal frequency of the actuator arm, the experiment is done using one selected model of the actuator arm and vary the inside diameter of the actuator arm into five different sizes as shown in Fig. 3. Each group consists of three pieces of specimen, and is called group 1 to group 5, respectively. The detail of each group is shown in Table 1. Group 3 represents the standard bore size. Group 1 and group 5 represent the too tight and too loose condition. Group 2 and group 4 represent the specimen with acceptable size. The outside diameter of the pivot bearing and the thickness of the tolerance ring were controlled by normal quality control standard. The specimens from each group will go through the standard assembly process. The process parameter such as the insertion force feedback has been record. After the assembly process, the actuator arm with pivot bearing was tested for their natural frequency using LDV (laser doppler vibrometer) and SLDV (scanning laser doppler vibrometer). The measurement setup is shown in Fig. 4. 3.3 Experiment Result Table 2 is the measurement result of the modal frequency at each mode of each group. The experiment shows that the modal frequency of mode 4 and mode 5 is significantly different in each group of specimen. Since the QC (quality control) standard considers the variation of measured natural frequency of the actuator arm that is greater than 300 Hz. The mode shape of the actuator arm is illustrated by Figs. 5-8. As the QC standard also mentioned the install force, the pivot bearing install force is recorded and shown in Table 3. The results show the relationship of the install force and the inside diameter of ACA. 4. The Numerical Method Result Since, the hard disk drive manufacturer try to find the process parameter that is directly relate to the Fig. 3 Illustrate ACA inside diameter. Table 1 The bore size of actuator arm. Group Bore size (mm) 1 (STD – 0.015) ± 0.002 2 (STD – 0.01) ± 0.002 3 STD ± 0.002 4 (STD + 0.01) ± 0.002 5 (STD + 0.015) ± 0.002 STD—standard size. Fig. 4 Measurement setup. Table 2 The modal frequencies (SLDV). Mode Modal frequency of each group (kHz) 1 2 3 4 5 1 7.23 7.10 7.37 7.42 7.47 2 11.52 11.59 11.53 11.56 11.60 3 15.36 15.44 15.38 15.49 15.52 4 26.90 26.72 26.31 26.51 27.01 5 30.72 30.71 30.15 30.58 30.34 6 38.53 38.51 38.37 38.51 38.59 7 45.11 45.29 45.22 45.21 45.43 modal frequency and its mode shape. The experiment done in this research might show some relationship between the controlled parameter and the modal frequency. However, the manufacturer could not complete every experiment for every assumption. The numerical method is introduced to solve this problem. The finite element model of the actuator arm is created
- 4. The Effect of Pivot Bearing Assembly Process on Natural Frequency of Actuator Arm304 Fig. 5 Illustrate the example of mode shape of the actuator arm at 15.4 kHz. Fig. 6 Illustrate the example of mode shape of the actuator arm at 26.5 kHz. Fig. 7 Illustrate the example of mode shape of the actuator arm at 30.1 kHz. Fig. 8 Illustrate the example of mode shape of the actuator arm at 38.4 kHz. Table 3 The average pivot bearing install force. Group Install force (kgf) 1 36.99 2 28.42 3 24.24 4 19.01 5 13.45 and is used for the modal analysis. The detail of ACA, tolerance ring, and pivot bearing are created, since the accurate result is expected. The finite element model of the APFA (arm-pivot-flex circuit assembly) is developed to compare the existence of the modal frequency and the effect of varying the ACA bore size. Fig. 9 illustrates the finite element model of the selected model APFA. The FEM result presents the same mode shape but slightly different modal frequency, as shown in Table 4. The significant different of modal frequency are also in mode 4 and mode 5. The mode shape from FEM is illustrated by Fig. 10. Table 5 shows the percent of different between the modal frequency from experiment and from FEM. 5. Conclusion The experiment results show the relationship of variation of the pivot bearing assembly in relation to parameters that affect the modal frequency of the actuator arm. The results also show the relationship of the install force and the inside diameter of ACA. Since the install force is subjected to the friction between the tolerance ring and the inner surface of ACA then, it could be assumed that the compressive force is also subjected to the inside diameter of ACA. The significant different of modal frequency exist only in some mode. The torsion mode is the only mode shape that is found significant different. The FEM result is agree with the experiment result. 6. Further Discussion The other factors should be considered as a testing parameter. The vibration in the vertical plane should be measure. The difficulties of the experiment is controlling
- 5. The Effect of Pivot Bearing Assembly Process on Natural Frequency of Actuator Arm 305 Fig. 9 The finite element model of the APFA. Table 4 Modal frequencies (FEM). Mode Modal frequency of each group (kHz) 1 2 3 4 5 1 7.17 7.21 7.26 7.28 7.33 2 11.30 11.33 11.34 11.36 11.40 3 14.76 14.84 14.94 15.09 15.12 4 24.60 24.72 24.84 25.11 25.51 5 27.62 27.71 27.96 28.25 28.58 6 35.35 35.41 35.48 35.51 35.59 7 40.91 41.19 41.25 41.31 41.43 Fig. 10 Illustrate the FEM arm bending mode. Table 5 Comparison of modal frequency result. Mode Modal frequency of group 3 (kHz) % error Experiment FEM 1 7.37 7.26 1.49 2 11.53 11.34 1.65 3 15.38 14.94 2.86 4 26.31 24.84 5.59 5 30.15 27.96 7.26 6 38.37 35.48 7.53 7 45.22 41.25 8.78 of the quality of the specimens, since there are a lot of part in the HDD (hard disk drive) could affect the modal frequency. The theoretical analysis might be applied to determine the relations of the variation of parameters to the modal frequency. Acknowledgments Special thanks to I/UCRC in HDD Advanced Manufacturing KMUTT (HDD-08-01-50 D) for funding support, Belton Industrial (Thailand), and DVG (Dynamics and Vibrations Group) Mechanical Department, Thammasat University for great support. References [1] W.L. Prater, Hard disk drive actuator assembly with damped tolerance ring for enhances drive performance during structural resonance mode, United States Patent, 6480363 B1 (2002). [2] N.E. Larson, Hard disk assembly having a pivot bearing assembly comprising fingers bearing on a shaft, United States Patent, 5757588 (1998). [3] J.R. Edwards, J.M. Garbarino, Disk drive having elastomeric interface in pivot bearing assembly, United States Patent, 5666242 (1997). [4] P. Ampaipipatkul, S. Sedsittichoke, S. Phopli, T. Phonpai, T. Jearsiripongkul, Vibration analysis of pivot bearing using LDV and identification using FEM, in: The 21st Mechanical Engineering Network Thailand, Chonburi, Thailand, 2007. [5] T. Jintanawan, C.P.R. Ku, J. Zhu, Effects of thrust hydrodynamic bearing stiffness and damping on disk-spindle axial vibration in hard disk drives, Microsystem Technologies 10 (2004) 338-344. [6] L.M. Xu, N. Guo, Modal testing and finite element modeling of subsystems in hard disk drives, Mechanical System Signal Process 17 (2003) 747-764. [7] J. Lue, D.W. Shu, Q.Y. Ng, R. Zambri, J.H. Lau, B.J. Shi, On the simulation of the pivot bearing inside HDD, Journal of Magnetism and Magnetic Materials 303 (2006) e81-e84. [8] F. Gao, F.F. Yap, Y. Yan, Modelling of hard disk drive for variation analysis using a flexible multibody dynamics formulation, IEEE Transactions on Magnetics 41 (2) (2005) 744-749. [9] L.M. Xu, N. Gao, Modal testing and finite element modeling of subsystem in hard disk drive, Mech. Syst. Signal Process. 17 (4) (2003) 747-764. [10] K. Ryota, T. Kazuhiro, I. Kenichiro, W. Singeru, I Takayuki, T. Kazuo, Modal analysis of HDD’s actuators, Fujikura Tech. 31 (2002) 7-12.