Article
Application of Piezoelectric Fast Tool Servo for Turning
Non-Circular Shapes Made of 6082 Aluminum Alloy
Marcin Pelic * , Bartosz Gapi ´nski and Wojciech Ptaszy ´nski
Citation: Pelic, M.; Gapi´nski, B.;
Ptaszy´nski, W. Application of
Piezoelectric Fast Tool Servo for
Turning Non-Circular Shapes Made
of 6082 Aluminum Alloy. Appl. Sci.
2021, 11, 7533. https://doi.org/
10.3390/app11167533
Academic Editor: Arkadiusz Gola
Received: 28 July 2021
Accepted: 12 August 2021
Published: 17 August 2021
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4.0/).
Faculty of Mechanical Engineering, Poznan University of Technology, 60-965 Pozna´n, Poland;
bartosz.gapinski@put.poznan.pl (B.G.); wojciech.ptaszynski@put.poznan.pl (W.P.)
* Correspondence: marcin.pelic@put.poznan.pl
Abstract:
The paper presents the design and testing of a new servo drive for turning non-circular
shapes. The presented solution is based on a commercially available piezoelectric drive unit with a
stroke equal to 1000
µ
m and a resonant frequency of 150 Hz. The device was used in a conventional
turning lathe and installed in a tool turret. The performance of the proposed tool was tested while
turning multiple non-circular contours from a cylindrical shaft made of 6082 aluminum alloy. The
machining accuracy was tested online using a laser sensor and offline with a coordinate measuring
machine. The additional aim of those tests was also to verify if the application of an online transducer
can allow a confident preliminary assessment of as-machined geometry. The drive positioning
accuracy was compensated using 6th order polynomial what resulted in the fabrication of non-
circular contours with an accuracy of no less than 39.8
µ
m when operating below the limit frequency
of the drive (<9 Hz). It was found out that the deviations of the profile from ideal geometries increase
linearly with frequency when turning at higher than the limit frequency.
Keywords: piezoelectric actuator; fast tool servo; non-circular turning process; mechatronics
1. Introduction
The production of parts of non-circular cross-sections in machining is no longer a
domain of milling. Such components can be efficiently produced by turning with the use of
lathes fitted with an additional drive. This technology can be based on a rotating tool as in
polygon turning [
1
,
2
] or a tool with feed motion operating in one [
3
–
5
] or multiple axes [
6
].
An example of such a process can be the manufacturing of middle-convex and varying el-
lipse pistons (MCVEP) widely used in diesel engines, which ensure better strain conditions
and guidance quality than circular pistons [
7
]. Other solutions concern polygonal shafts
fabricated without halting the turning process. Driven tools with feed motion referred
to as Fast Tool Servos (FTS) are usually controlled by electronic cams that couple the tool
linear position with the part angular position following a strict mathematical relation. The
technological requirements set for such tools usually exceed the dynamic capabilities of
conventional servo drives (e.g., with an electric engine and ball-screw transmission) due to
the difficulties with synchronizing the tool’s high-frequency reciprocating motion with the
rotational speed of the spindle. Linear motion drives are a group that can potentially solve
the dynamics issues to some extent. The solutions featuring high dynamics include the
Voice Coil Motor (VCM) [
8
,
9
] or piezoelectric actuators. The latter is in the form of stacks
and is characterized by high force, rigidity and dynamics. However, they exhibit a limited
travel distance which is mostly related to the size of the stack, what can be troublesome in
some physical application due to the limited available workspace in the machine. Solid
flexures [
3
–
7
,
10
–
16
] reinforcement frames acting as rhomboids that enable achieving a
millimeter long travel range but at the cost of deteriorating other performance parameters,
especially force and rigidity.
An important feature of a piezoelectric drive is its hysteresis which affects the posi-
tioning accuracy while operating in an open-loop system. The hysteresis error can amount
Appl. Sci. 2021, 11, 7533. https://doi.org/10.3390/app11167533 https://www.mdpi.com/journal/applsci
