stacked Hybrid Systems with Separated Sensor Design
Stacked Hybrid Systems with one Common Position Sensor
For the last decades ultra-precision positioning technology was mainly driven
by the semiconductor industry. In the 1990’s The opto-electronic
telecommunications boom was the starting point for radical new technologies such
as very compact multi-axis systems capable of nanometer level resolution and
automated alignment tools. With the emergence of nanotechnology came the need
for new types of precision positioning tools that go beyond the requirements of
the conventional semiconductor sector. But also the roadmap of the semiconductor
industry requires novel nanopositioning systems capable of even higher
resolution over larger travel ranges because the wafer sizes keep going up.
Traditional motor drives can be used for large movements, but the resolution
is far from the requirements for nanotechnology. This paper describes new hybrid
systems designs such as the combination of piezoelectric and motorized
systems with a long travel ranges and extremely high resolution, controlled
by one sensor and one servo system.
Serial stacked Hybrid Systems
with Separated Sensor Design
With the emergence of nanotechnology came the need for new types of precision
positioning tools that go beyond the requirements of the conventional
semiconductor sector. The functional structures of nano-devices are on the
nanometer or even picometer range. Yet the dimensions of the entire devices are
in most cases much larger. Thus, there are two new mechanical requirements:
large travel ranges (up to one inch or more) and – at the same time – extremely
accurate positioning with nanometer or sub-nanometer resolution.
Furthermore, a higher number of axes are often necessary.
Specially designed piezo
positioning systems meet the above requirements. Paired with capacitive
sensors, they allow for controlled sub-nm motion.
Figure 1. Example of a serial stacked hybrid system
featuring a high-speed coarse positioning over a large range: 25 x 25 mm in x
and y (a) and piezo stage for fine positioning: Up to 6 axes (2 axis stage shown
here), down to sub-nm resolution (b).
Table 1.Comparison of piezoelectric and motorized motion
10 to 1000 [µm]
5 to 1000 *103 [µm]
Incremental optical sensor
About zero for static position
Passive sensor probe & target
Small Motor power
Hybrid Systems with one Common Position Sensor
Hybrid systems consist on the combination of both:
For the maximum absolute positioning accuracy, the controller should rely on
only one position sensor for both the coarse and fine positioning ranges. The
following sketch shows a variety of hybrid designs with sensors, that measure
the complete travel range.
Figure 2.(a) Mechatronic Hybrid system featuring high
resolution optical incremental sensor providing 2 nm resolution and a motor
driven stage combined with flexure guided piezo actuator for 100mm travel range.
(b) Hybrid leadscrew (spindle) / nut systems with piezo fine adjustment.
Promising solutions for hybrid actuators are the combination of:
- Leadscrew/nut or ultrasonic piezo drives & PZT linear actuators in the
- Leadscrew/ nut & PZT linear actuators in the nut (stack or tube)
- Piezo ultrasonic drives with additional analog mode
- PiezoWalk® drives
The motor driven unit can be described as a combination of a resonant system
and the motor part. Both the motor driven part and the piezo actuators have
resonant properties. For fast response these resonant terms should be cancelled
by notch filters.
Figure 3 shows the control structure of the hybrid system.
Figure 3.Structure of the hybrid controller.
The control structure consists of two paths: One to control the motor
position using the incremental optical sensor; a PID and a notch filter; and a
PWM driver to provide power to the motor.
The piezo path consists of the same optical sensor as reference and uses a PI
filter and a notch filter.
Some level limits are necessary to stabilize the control function and prevent
overflow errors in the D/A or D/PWM parts.
An additional I – term was added in the motor path, which is designed to drop
the piezo voltage, when the system approaches the target position. Because both
the motor and the piezo actuator operate on the same position target, it would
be possible for the piezo voltage to max out when the stage reaches the target
position. The voltage can be reduced by this additional I- term with a lower
time constant than the piezo part.
The controller outputs a voltage range of +/- 10V to the piezo in static
mode, a few milliseconds after a step.
shares/splits the response between the piezo actuator and the
motorized stage. The piezo actuator is driven at a higher bandwidth than the
motorized actuator. Otherwise both actuators would try to compensate for their
The controller is based on a two hardware-synchronized PC cards. One card
reads and buffers the encoder pulses for the PC access, the other one works as
the D/PWM output and drives the amplifier. An incremental optical encoder with
4µm pitch and 1000 times interpolation module was used to achieve a resolution
of 4nm over a travel range of 100mm. The controller concept shows that the
actual position is stable to one encoder count of 4nm.
New encoders with sub-nanometer resolution are now available and can be used
with the system.
The research & development of nanotechnology systems requires new
positioning tools with extremely high resolution combined with a large travel
range. New controller
and actuator designs show that a hybrid approach with electromagnetic and piezoelectric actuators
together with high resolution incremental encoders and capacitive sensors
provide the most flexible technology.
Source: PI USA
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