Modules of additional drive circuitry have been developed to enhance the functionality of a family of commercially available positioning motors (Picomotor™ or equivalent) that provide linear motion controllable, in principle, to within increments ≤30 nm. A motor of this type includes a piezoelectric actuator that turns a screw. Unlike traditional piezoelectrically actuated mechanisms, a motor of this type does not rely on the piezoelectric transducer to hold position: the screw does not turn except when the drive signal is applied to the actuator. In the original application for which these modules were developed, a clockwise-vs.-counterclockwise asymmetry in the pulses generated by a driver module that operates at a rate of ≤1 kHz made it impossible to reliably command the advertised ≤30-nm steps in either direction. In addition, the original application involved low-duty-cycle operation, which offered the opportunity to reduce cost by using a single driver module with multiplexing circuitry to drive several motors. There was an additional desire to modify the motors by integrating limit switches into them to provide calibration and position-reference signals.
Because of the highly specific nature of its origin, a module of the present type is denoted a Picomotor break-out box. It is designed to be installed and operated in conjunction with (1) an improved, high-voltage driver module, developed specifically for use with a motor of the type in question, that operates at a rate ≤2 kHz; (2) a commercial digital input/output module; and (3) a commercial counter/ timer module. Among other things, a Picomotor break-out box affords a capability for multiplexing of output for low-duty-cycle control of as many as 16 motors. The circuitry in the break-out box includes a commercial gate array that can be triggered by a limit switch to immediately stop the pulse train fed to the driver module, thereby eliminating what would otherwise be the latency involved in stopping motion via software. Also included in the break-out box are power supplies for the driver module and accessory signal boards. The break-out box and the driver box are connected by a single cable that can be up to 130 feet (39.6 m) long, so the thermal pollution of the power supplies can be physically isolated from the actuators.
This work was done by Robert Smythe, Dean Palmer, Yekta Gursel, Leonard Reder, and Raymond Savedra of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-30359
This Brief includes a Technical Support Package (TSP).
Additional Drive Circuitry for Piezoelectric Screw Monitors
(reference NPO-30359) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory, detailing the functional specifications for Picomotor Break-out Boxes designed for controlling piezoelectric screw motors. These break-out boxes serve as transition modules that connect two standard Industry Pack Modules—the Greenspring IP-Digital 24 (digital I/O) and the Acromag IP480-6 (counter timer)—to the high-voltage New Focus 8702 OEM driver module for the Picomotor system.
The break-out box is a 1U high, 19-inch rack-mountable unit that facilitates the connection of the IP modules via two 50-pin SCSI cables. Each IP card can control up to 24 Picomotors, divided into two groups of 12, accessible through two DB25 connectors. The unit is equipped with internal power supplies, providing +5V, ±15V, and +12V at 2A to power the Picomotor controller boxes.
Key components include an Altera EPM7032SLC44-10 gate array, which plays a crucial role in managing the output pulse-train to the Picomotor drive module. This gate array is programmed to disable the output when an active limit switch is triggered, enhancing the system's responsiveness by eliminating software latency.
The document outlines specific configuration requirements for the modules. For instance, the Greenspring IP-Digital 24 requires a jumper to be added to position E20 to share its +5V supply with an Altera FPGA. Additionally, driver chips U25 and U27 must be replaced with 74HCT2245 chips to ensure adequate drive current for the Opto-coupled inputs of the Picomotor drive module. The IP480-6 module also requires a resistor change from 4.7KΩ to 1KΩ for similar reasons.
The front panel of the break-out box features connection points, including two SCSI connectors and two DB25 sockets, along with three LEDs that indicate the health and operation of the internal power supplies. Jumper settings for the Altera gate array are specified to ensure proper functionality.
Overall, this document serves as a comprehensive guide for configuring and utilizing the Picomotor Break-out Boxes, providing essential information for engineers and technicians involved in aerospace applications and motor control systems.
