By Dave Henderson and Lisa Schaertl, New Scale Technologies, Victor, NY
Here’s what happened in a multi-year collaboration among engineers and scientists at New Scale Technologies, austriamicrosystems and TDK-EPC to simultaneously develop the motor, mechanics, electronics and control systems for the M3 piezoelectric micro motor.
Larger-scale mechatronic systems include this integrated size 17 stepper motor and IDEA drive from Haydon Kerk.
Piezoelectric micro motors satisfy the need for linear motion in miniature products. These millimeter-scale motors are less than half the size of solenoids or traditional electromagnetic micro motors. They are more efficient at small sizes, and produce direct linear motion without gears or drive trains. They also offer longer travel, higher precision and higher force than solenoids or shape memory alloys (SMAs). These features make them suitable for use in portable battery-powered devices, such as miniature focus systems for cameras in phones or industrial laptops, or any application requiring small size and high precision. These include machine vision, optical fiber and RF tuning devices, medical devices, and military systems for vision, targeting and control.
自2006年以来,花体压电电机系统ms have shrunk in size from (at right) a 12 mm diameter motor with 51 x 76 x 14 mm drive card, to (at left) a 2 x 2 x 5 mm motor with a flip-chip drive ASIC (shown on the dime). This enabled the creation of integrated micro-mechatronics modules such as the M3-L module (center) – complete closed-loop motion systems in housings of less than 7 x 12 x 30 mm.
Designing with piezoelectric (piezo) motors requires a different mindset than that used with traditional servo or stepmotors. The traditional approach of specifying the motor and then buying or designing the control system works for servo and stepmotors because there is a vast body of “cookbook motor” control solutions and experienced drive teams available for traditional motor implementation. This is not the case for piezo motors, which require special drive circuits to create and maintain ultrasonic resonant vibrations in the motor.
此外，当机械，电子，控制系统，软件甚至电动机设计本身时，压电电动机最有效。通过这种方式，可以将压电陶瓷，硅和系统调整为最佳性能。它是机电设计过程的好处的完美说明。
Miniaturization meets mechatronics
The last five years have seen impressive miniaturization of piezo motors. One example is our SQUIGGLE motor. Recent innovations have yielded dramatic reductions in the size of the drive electronics. Such reductions were possible in part through collaboration with TDK-EPC to develop new, lower-voltage piezo actuators and eliminate the need for voltage boost circuits; and in part by work with analog IC experts at austriamicrosystems to incorporate more intelligence into the piezo drive ASIC.
These advances enabled new integrated micro-mechatronic modules: small closed-loop actuators that serve as simple “drop in” subsystems in OEM product designs. The system designer provides high-level commands to the module through a standard serial interface. A 3.3 Vdc battery provides power. The mechanical coupling is customized to the application: to move a lens, adjust a grating, push a valve, and so on.
Such micro-mechatronic modules typically provide as much as 50 grams force with precision of one-half micron and closed-loop accuracy measured in tens of microns.
Mechatronics compared to micro-mechatronics
In some ways these micro-mechatronic modules are analogous to larger versions. However, there are important differences. For example, Haydon Kerk combines its IDEA drive with a size 17 stepper motor to create an integrated 60 x 40 x 70 mm mechatronic system that is PC-programmable. According to Haydon Kerk’s Ray LaChance, this integrated drive system is for designers who need a few thousand units per year. Design teams making higher-volume products typically create their own drivers, relying on experienced in-house drive teams and libraries of standard drive approaches.
In contrast, driving piezo motors requires specialized knowledge and experience to create control systems that optimize the motor and drive performance under a range of conditions (including varying input voltage, duty cycle, environment, and load). Load coupling techniques are also important for maximum performance and operating life.
The latest drive ASIC for the SQUIGGLE motor incorporates numerous drive functions that in earlier versions were implemented off-chip. The result is a reduction in overall system size.
Innovation miniaturizes components
Our initial focus was to reduce the size of the motor. The SQUIGGLE motor design has proven to be highly scalable, shrinking by a factor of 100 since the first model was introduced in 2004. The current model measures less than 3 x 3 x 6 mm with housing.
Unlike other piezo motors, where the piezo elements push directly on a stator, this design uses ultrasonic vibrations of the piezo elements to create resonant orbital vibrations in a nut. These minute vibrations drive a threaded screw forward or backward, creating direct-drive linear motion. In this design the piezo ceramics are decoupled from the load path, enabling high force and robustness.
The innovations that allowed miniaturization of this motor included the ability to machine tiny screws with precision threads, greater material choices, fine-tuning the geometry of the piezo ceramics, and creating micro-manufacturing processes for semi-automated and automated assembly of the tiny components.
Next the company turned its focus to miniaturizing the drive electronics. The input to the piezoelectric elements is a set of phase-shifted waveforms that match the resonant frequency of the motor. While other techniques are used, motor speed is typically controlled by varying the amplitude of the voltage.
努力使小型化的司机,团队zeroed in on the need to reduce the voltage level required to excite the piezoelectric elements. Like most piezo motors, SQUIGGLE motors employ “hard” PZT ceramic material to minimize dielectric losses and associated temperature rise. This material requires an applied voltage of around 40 V to create motion. For battery-power operation, this necessitated a dc-to-dc step-up converter in the drive ASIC, as well as external components to regulate and boost voltage. While total drive footprint for these components was approximately 6 x 9 mm, many OEMs wanted even smaller drivers. Some, especially in medical applications, were uncomfortable with the presence of 40 V in the system even though the drive IC operated on 3.3 V battery power.
In 2008, we partnered with TDK-EPC to develop a piezoelectric drive element with reduced input voltage requirements. The resulting element consists of multiple thin layers of hard piezo ceramic material, co-fired into a single plate. It has the same dimensions and performance as the original monolithic element, but requires only 2.8 V applied voltage.
这种变化消除了对升级转换器和增强电路的需求，并允许Austriamicrosystems为减速电机创建较小的驱动器。通过这种迭代，Austriamicrosystems也从QFN包装转移到了晶圆级芯片刻度包装（WLCSP），将ASIC从4 x 4 mm缩小到1.8 x 1.8毫米。仅需要两个外部电容器，对于2 x 3 mm的总驱动电路足迹。
同时，设计团队将更多功能包装到较小的芯片中，以增强电机和系统性能。例如，片上的频率生成消除了对外部时钟的需求。混合动力全桥/半桥驾驶员更换了半桥版本，使驾驶员可以调节电动机的电压，并自动切换驱动程序以较慢的速度节省电源，或者随着电池电压下降而持续的速度。这些功能将系统功耗降低了30％以上，为电池供应应用提供了额外的好处。
新ASIC中的其他功能包括正在申请专利的技术，以监视电机性能并调整驱动频率，以保持电动机的机械谐振频率的锁定，这可能随温度而变化。这样可以确保在宽温度范围内的最佳运动性能和高功效周期。
小型化可以实现微型机能
With the drive electronics now smaller than the motor itself, the design team created closed-loop control systems using these components.
SQUIGGLE motors have good position resolution: pulsing the drive signal can cause the motor to move distances as small as half a micrometer per pulse. However, the motor speed—and hence distance travelled per pulse—will vary with applied load and device friction. A closed-loop control system is needed to achieve exact positioning, repeatable bi-directional positioning, or precise speed.
The ability to integrate closed-loop controls into a micro module was aided by recent advances in non-contact position sensors and microprocessors.
The TRACKER position sensor, a joint development by New Scale and austriamicrosystems, is a non-contact magnetic encoder that gives direct digital output, eliminating the need for external pulse counters. At only 3 mm total height including the magnet, it is smaller than optical encoders with glass slides and does not require a light source, which is of particular benefit in optical lens positioning applications. The sensor has a built-in zero reference and 0.5 μm resolution.
A 2.4 x 2.4 mm mini microprocessor integrates into a module with the motor, driver and position sensor. The microprocessor is small and inexpensive enough to allow the company to add intelligence to the module with negligible impact on cost or size. The microprocessor receives position information from the position sensor, and uses on-board PID control to adjust the motor drive signal based on proximity to the target position.
嵌入式系统中,该模块接受high-level ASCII commands from the system controller through standard serial interface (I2C or SPI). The command set includes commands to set the motor speed, move, halt, move a specified distance, and move to a target position.
因此，该模块可用于许多运动任务。移动到目标位置命令允许模块传输到任何数量的预设位置，例如移动光栅以调整激光器为选定的波长。移动和停止命令可用于移动执行器，直到达到给定条件，例如在自动焦点系统中。摄像机模块开发人员使用其自动焦点算法来命令执行器，以在达到焦点时朝任何方向移动镜头。
Motor, driver, position sensor and microprocessor are integrated to provide closedloop linear motion with simple high-level command input via standard serial interface.
The ability to use high-level ASCII commands to move the actuator dramatically simplifies the task of embedding precise micro motion into a system design. For evaluation and testing, a USB adapter lets users connect the module to a PC and end commands to the module using the graphical user interface of New Scale Pathway software.
M3微动物模块证明了使用机器人设计过程的优势。如今，工程师正在使用这个微小的系统级执行器来添加电动焦点以紧凑的生物识别传感和机器视觉摄像头，并创建紧凑的RF和光学调整系统。
新的规模技术
www.newscaletech.com
austriamicrosystems
www.austriamicrosystems.com
海顿·克克（Haydon Kerk）
www.haydonkerk.com
TDK-EPC
www.tdk-epc.us
Filed Under:Factory automation,设计世界文章,编码器•光学,Mechanical,运动控制•电动机控制,Mechatronics
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