Mechanical motion adds precision
to eye surgery
Edison, NJ--A new surgical technique offers quick, precise cuts and less cornea trauma to patients undergoing eye surgery. The waterjet cutting technique, called the Hydro-bladeTM keratome, was developed by Edison, NJ-based Medjet Inc. Medjet President Eugene Gordon says, "The Hydroblade nurtures cornea-tissue healing and stability, and may make corrective lenses obsolete for individuals with myopic, hyperopic, or astigmatic vision impairments."
The approach, already tested on animals and human-donor eyes, is scheduled for minimal testing on blind patients early this year. "In only a few weeks, tissue stability will be determined," says Gordon. FDA approval is expected by the middle of 1997.
Surgical blades have been used for forty years to reshape the cornea, according to Gordon. "The neat waterjet cleave makes blade cutting appear barbaric in comparison. We hope this procedure will enable more precise correction of the cornea's shape. In addition, less tissue damage may promote more stable healing and less haze, enabling little or no loss of visual acuity."
Ruby heart. Vision impairments are corrected by removing just enough tissue from the cornea to make it the shape of a proper lens. The template and cutting plane determine the cornea's final shape. During a typical procedure the ophthalmologist determines the refractive correction in diopters, selects the appropriate cutting head (including the proper template and orifice), and snaps it onto the device.
The doctor uses a microscope to position the template over the center of the cornea. The template applanates or flattens the cornea slightly, while a globe fixation device stabilizes the eye in the instrument.
As the doctor steps on a foot pedal, the template prevents involuntary eye movement. The total cut takes less than one second, and moves so quickly that inertia maintains the cornea's position. The cut removes a contact-lens-shaped piece of tissue with a specific refractive power to correct the patient's vision impairment.
| Did you know... 53.3% of all engineers surveyed specifiy 1- to 10-hp motors. Source: Design News Market Beat survey. Did you know... 69.6% of engineers surveyed specify permanent- magnet motors. Source: Design News Market Beat survey. Did you know? 50.9% of engineers surveyed specify single-phase induction motors. Source: Design News Market Beat survey. |
The 30-micron-diameter waterjet uses 1 ml of "immaculate" water to break only the bonds required to part the tissue in a natural way. A ruby orifice supplied by Bird Precision (Waltham, MA) is the heart of the nozzle.
A servo-controlled test system was instrumental in the technology's development, according to Gordon. Medjet used the final positioning parameters, determined experimentally, to design the miniaturized rack-and-pinion system and lead screw for the completely mechanical prototype.
The test system employs a Compumotor 6250 2-axis servo controller that commands the dual axes. Yaskawa (Japan) SGM brushless dc motors with integral encoders turn lead screws to drive each axis.
Air-powered rifle. Powering the mechanical motion system is a stock Leeland liquid-CO2 cartridge obtained from the North Plainfield, NJ-based supplier. "When the doctor's foot depresses the pedal, a CO2 charge is released, much like pulling the trigger of an air-powered rifle," says Gordon. An Aerodyne Controls (Ronkonkoma, NY) regulator curbs the line pressure at 700 psi.
Carbon dioxide gas at 700 psi flows through a plastic tube to the instrument and into a water intensifier. The force of the gas exerted on a 1-inch-diameter piston pressurizes water up to 20,000 psi. At that pressure, the 0.36-micron ruby orifice limits the water's flow rate to about 1 ml/sec.
The constant flow rate of the essentially incompressible water makes the intensifier act like a dash-pot, maintaining constant piston velocity. A rack-and-pinion gear system converts the piston's linear movement into rotary motion that is transmitted to a lead screw by a steel belt from Agawam, MA-based Belt Technologies.
The lead screw drives the cutting head at a speed of 10 mm/sec and the average scan length is about 8 mm. A typical cut will take less than a second and use just under 1 ml of water. dn
--John Lewis, Northeast Technical Editor
Servos solve complex motion problems
Seal Beach, CA--Packaging machinery for some applications can involve extremely complex motion. Just ask Arkady Livitz, electronic engineering manager at Arpac LP (Schiller Park, IL). Describing the servo-driven functions within the company's new fruit-juice packaging machine, Livitz says, "It's hard to visualize, it's like a circus in there."
The new machine has to package unstable 8-oz. juice bottles into eight packs by wrapping them with plastic film.
The process begins by grouping eight bottles to a pack. A flight bar, driven by a variable-speed motor, then pushes the pack along a conveyor. An encoder provides feedback, and the flight-bar's motion serves as the master input for two slaved axes.
One slave is a vacuum conveyor that runs under the machine. It makes a sinusoidal motion, alternating between low and high speeds by means of a Compumotor (Rohnert Park, CA) 6000 Series controller. The second slave axis drives the film feed, which moves in unison with the conveyor. When the film gets to a certain length at a registration mark, the controller signals to cut the film.
The 6000 Series' phase shifting and position-based following features makes the complex sinusoidal motion possible, but a new feature, cam motion, makes the application practical, Livitz says.
Cam motion incorporates pre-compiled, position-based following to reproduce mechanical cam motion. This allows the master to move forward or backward while the slave axis moves forward or backward through its cam motion. The result: The new machine can recover from an error without having to home.
Drive simplifies parts cleaning
Seal Beach, CA--Take a close look at this page. Its crisp text and uniform graphics may be the result of a printing-press roller cleaned with Micro CleanTM, a pneumatic blasting system made by Temple Associates (Rancho Cordova, CA) that uses a proprietary beaded-plastic medium. The machine leverages an integrated drive/controller called Smart Drive to simplify its design, programming, and operation.
Micro Clean consists of a blast cabinet containing an adjustable lathe to which the print roller is mounted. During cleaning, a pneumatic spray head passes the length of the roller while shooting media. At the end of the stroke, an ac motor rotates the roll a specified amount, and the head passes back the other way.
The Smart Drive controls a step motor that powers the traversing spray head, the rollers rotation, blowers, solenoids, and the pneumatic system.
"One black box controls the entire machine," says Rick Knox, product marketing engineer at Industrial Devices Corp. (No-vato, CA), manufacturer of the Smart Drive. "The customer didn't have to integrate a PLC, I/O, or operator interface from another manufacturer."
Don Temple, vice president of Temple Associates, was already a fan of IDC's rodless actuators when he came across the company's Smart Drive. In fact, an R2 Series cylinder drives thespray-head traverse. Its sealed design prevents dirt and media from gumming up the actuator. "This was a major step forward," Temple says. "Before, the mechanism all had to be driven from outside the cabinet."
Controller maximizes pick-and-place performance
Seal Beach, CA--Take three mutually exclusive criteria for a motion system--speed, precision, and smoothness--and specify that each be optimized. That's a description of Bill West's job.
As electrical engineering manager for Quad Systems Corp. (Horsham, PA), West headed up the design of the motion-control system for Quad's family of surface-mount-technology (SMT) circuit-board assemblers. The company's model QSP-2 can place a maximum of 14,000 components per hour. The cost-effective controller had to handle 50-100 commands in 700 msec.
"The name of the game is components per hour," West says. "We looked for a controller with a balance between the software and controls aspects--some products are great at one or the other; MEI's were good with both." MEI stands for Motion Engineering, Inc. (Santa Barbara, CA). Two of the company's four-axis DSP cards are used in Quad's QSX-1 and QSV-1 models, while three cards handle the QSP-2's twelve axes.
The machines work by moving a vacuum nozzle on an X-Y gantry to select parts from a tape feed, and then orienting and placing them on circuit boards. Linear dc brushless motors power the QSX-1, while the QSP-2 model uses a belt drive. Positional resolution exceeds 0.001 inch, even while placing about four parts per second (QSP-2). "It has to be smooth and settle quickly," says West. "Some parts are expensive, and customers don't want jerky motion."
He based much of his decision on an internal contest between four cards, but also favored MEI's design philosophy. "They had a lot of features that I would have put in myself," he says.
Breakthrough designs with motion control
Miniature step motor
Empire Magnetics' (Rohnert Park, CA) Size 5 step motor emerged from a cooperative research and development agreement (CRADA) with Lawrence Berkeley Laboratory (LBL). About a half-inch in diameter, it boasts a true 1.8-degree step size, unlike the 15- to 90-degree steps of competing designs. The secret? Precise, tiny features courtesy of deep-etch X-ray lithography.
Unlike conventional lithography, the LIGA X-ray process can expose and develop resists 5-mm or more thick, not just microns. Parts are electroplated in nickel-iron into the developed resist, requiring an X-ray exposure each time. LBL researcher Keith Jackson ultimately plans to use LIGA to create molds--instead of the parts themselves--that could then be used to mass produce the components.
Fifty rotor and stator laminations 1-mm thick stack to form a complete motor. Possible applications include satellites, cameras, and surgical instruments. Challenges? Wire-winding the tiny prototypes that will be available early this year.
--Mark A. Gottschalk, Western Technical Editor
Application Tips
How to match servo amplifiers to brushless dc servo motors
Terry Auchstetter, Product Mktg. Engineer, Bodine Electric Co., Chicago
Many manufacturers offer motor/amplifier packages, but performance gains often result from specifying servo-system elements from different manufacturers. The following considerations will help match a servo amplifier with a particular brushless dc motor.
- Amplifier should produce a square wave current for brushless dc motors.
- The amplifier must be configurable to accept feedback from the motor's commutation sensor configuration.
- Check that the amplifier's mode of operation is configured to match the application--either current mode, velocity mode, or open-loop mode.
- Select a motor using the applications' load and speed requirements. Then calculate the required supply voltage. The amplifier's output voltage should be at least equal to the calculated voltage.
- The amplifier's continuous current limit must exceed the calculated RMS current required to drive the load. And the amplifier's peak current limit should exceed the motor's current draw during peak loading conditions, while staying below the motor's demagnetization limit.
To speak with a Bodine Electric applications engineer, call (773) 478-3515.
Application Tips
How to smooth out CCD scanners
Philip Santarelli, Manager of Marketing & Sales Promotion Oriental Motor USA Corp., Torrance, CA
Charged Coupled Device (CCD) scanners, in their simplest form, turn light into a signal. Typically, CCD scanners use a step-motor system because a one-to-one correspondence can easily be made between a discrete number of motor steps and a desired number of lines to be exposed on the moving CCD.
Smooth motion is crucial, as any system vibration will blur the picture.
Although a step motor's cardinal step is always the same, this is not the case when microstepp-ing, since electronic manipulation of current is usually not constant.
A solution is the standard five-phase system, run at half step, which allows for the same smoothness as a two-phase microstep system while maintaining equal step sizes.
Many images require even higher resolution. Reduction gearing works, but slows the sys-tem down, possibly adds backlash, and takes up ex-tra space. A better wayto increase resolution isto use a five-phase mi-crostepping system that has equal-sized steps. The New Pentagon technology used in drivers, such as the NanoStep(R) systems from Oriental Motor USA Corp., allow for accurate control of the position vector so variations in input current (or voltage) will only change the magnitude of the signal--not the angle--leading to equal step size.
To speak with an Oriental Motor applications engineer, call (310) 325-0040.
Products to watch
Drivers, controllers, motors
Six-page color brochure on the new DeltaMax line of integrated driver controllers and motors provides complete details on 25 compact, all-digital controllers and motors, plus design and specification information, including power output, rated and maximum speed and torque, rotor inertia, motor and shaft dimensions, and more. DeltaMax features an active servo axis with one-half axis follower, fiber-optic input combined with a range of high power-density motors.
Industrial Indexing Systems, 626 Fishers Run, Victor, NY 14564, FAX (716) 924-2169.
State language tutorial
Take a 61/2 minute tour of QuickstepTM for WindowsTM State Language. A free demonstration disk and 12-page booklet show how fast and easy-to-use state-language programming can be. Going through an actual recorded programming session for a bottle capper application shows how state-language can help integrate various machine-control environments. Complete integration of motion control, sequencing, analog I/O and communications all programmed in one language may change your approach to machine automation. "Integration means plug-and-play with existing equipment and less operator training," says CTC's Marketing Manager Scott Pete. "Greater access to process information helps to optimize control."
Control Technology Corp., 25 South St. Hopkinton, MA 01748, FAX (508)-435-2373.
Single-axis controller fits in tiny spaces
Need limited motion control and pinched for space? Consider the DMC-1411, a controller card for one-and-a-half axes. It uses a 32-bit specialized microprocessor and controls both servo and step motors. Measuring just 3.6 by 3.8 inches, the DMC-1411 meets the PC/104 specification that has become a de facto standard in the embedded-control industry, the company says. Control is provided by a 16-bit motor-command DAC and PID filter. The program memory--250 lines by 80 characters--allows the control of custom applications without using the host PC. Possible motions include jogging, point-to-point positioning, electronic gearing and CAM, and contouring.
Galil Motion Control, 203 Ravendale Drive, Mountain View, CA 94043, FAX (415) 967-1751.
Open CNC interface works in Windows
The 9/Series Open CNC Interface (OCI) is a PC-based data-access window that provides full operator interface in a Windows NT environment. It's said to give OEMs an open-systems option for machine customization using standard development tools. For example, the 9/Series standard operator displays are written in Visual Basic, allowing complete freedom to optimize the contents, says marketing manager Mark Devonshire. "Users have a flexible platform to implement third-party manufacturing and communications products."
Allen-Bradley Response Center, Dept. 0254, 10701 Hampshire Ave. S., Bloomington, MN 55438, FAX (800) 500-0329.
No need to program this controller
Just point, click, and move, says the company about the Si5580 Step Motor System. Designed for precision, power, and ease of use, the controller uses the MS Windows graphical user interface to take advantage of today's most advanced software tools. It does the programming; the user need only input the move parameters. The Si5580 consists of a microstepping drive, 80V-dc linear power supply, and state-of-the-art controller, all packaged in a compact enclosure. Motor resolutions range from 2,000 to 50,800 steps/rev. Software is Windows 3.1 and Windows 95 compatible.
Applied Motion Products, 404 West-ridge Dr., Watsonville, CA 95076, FAX (408) 761-6544.
One small step for mankind
The PMU Series five-phase hybrid step motor is said to be the world's smallest, and it's matched with the world's smallest 115V-ac driver. The PMU33AH motor (0.72-degree full step) produces a constant 3.3 oz-inches of torque over a speed range of 100 pps to 40,000 pps (4,800 rpm). It measures just 1.150-inches sq. by 1.22-inches long, occupying just 1.10 cubic inches. It's matched with a driver measuring 1.38 x 4.34 x 5.32 inches. The 115V, 60-Hz, ac input is converted into 4- or 5-phase New Pentagon excitation scheme for full- and half-step operation. It incorporates a special low-vibration circuit for quiet operation.
Oriental Motor USA, 2580 W. 237th St., Torrance, CA 90505, FAX (310) 325-1076.
Rodless actuators handle high loads
Newly designed rodless linear actuators handle higher loads, higher power, and higher speeds. Called the R Series, they feature ready-to-mount motor and actuator systems in travel lengths up to 108 inches, and speeds up to 120 inches/sec. The actuators handle thrust loads of up to 1,200 lbs. Three models are available: R2, R3, and R4. The smallest, R2, has a 2 x 2-inch crossection, whereas the largest, the R4, has a 4 x 5-inch crossection. All can be had with choice of acme screw, ball screw, or high-speed steel-reinforced belt drive.
Industrial Devices Corp., 64 Digital Dr., Novato, CA 94949, FAX (415) 883-2094.
Slim controller stands onits own
Otek's HI-Q123 programmable intelligent controller is designed for hazardous duty. A NEMA 4x Lexan overlay protects an analog bar graph that quickly relays vital process information to the operator at 1% accuracy. The seven-segment, six-digit display gives digital precision while the colorful backlighting and blinking visual alarms trim the built-in keypad. The controller has dual processors, real-time clock, isolated 16-bit A/D and four-channel analog multiplexers. The 4.5-inches sq. by 1-inch deep controller also includes signal conditioners and serial I/O. An optional I/O module adds an additional 1.5-inch depth. The explosion-proof model comes in cast aluminum or a 94 VO-rated ABS polycarbonate.
OTEK Corp., 4016 E. Tennessee, Tucson, AZ 85714, FAX (602) 790-2808.
Driver leverages Windows NT features
MEI has a Windows NT driver for its complete line of C-programmable motion controllers. The new driver enables system developers at volume OEMs to leverage the full multitasking and interrupt handling capabilities of Windows NT in complex motion-control applications. With the driver, designers can use Windows NT's multitasking capabilities to maximize resource use and ensure real-time performance for multiple motion controllers. "Windows NT has become volume OEMs' system of choice for sophisticated motion control applications," says CEO Matt Cheresh. "MEI is the only motion-control vendor to offer such broad support for it."
Motion Engineering Inc., 33 S. L Patera Lane, Santa Barbara, CA 93117, FAX (805) 681-3311+6.
Touch screen needs no programming
The TS-3200-FP color touch screen reportedly offers brilliant graphics and excellent machine-control functionality in a low-profile design. The 10.4-inch TFT active matrix display provides a graphical machine interface that requires no screen integration or programming. Within hours after unpacking, users can auto-tune and run servo axes, configure and test I/O, and diagnose hardware using the touch screen and the company's MachineWorksTM Controller.
Berkeley Process Controls,1001 W. Cutting Blvd., Richmond, CA 94804, FAX (510) 236-1186.
Controllers boost performance
New hardware and software enhancements raise the upper limit of performance and increased capabilities for the PMAC and PMAC2 families of motion controllers. Option 5C provides an 80-MHz Motorola 56002 DSP, zero wait-state RAM, and flash-memory backup for programs and tables. This yields more than five times the computational rate of the base version PMAC. New version 1.16 firmware provides new capabilities, such as: non-uniform cubic B-spline interpolation, automatic go-until-trigger moves, torque-limited homing and triggered moves, teach/learn, backlash and torque compensation tables, and more.
Delta Tau Data Systems Inc., 9036 Winnetka Ave., Northridge, CA 91324, FAX (818) 998-7807.
Package simplifiesprogramming
Industrial Indexing Systems' DeltaPro is a 11/2-axis motion solution that includes positioner, power supply, and motor in a single, easy-to-spec configuration. Applications include indexing, positioning, profiling, electronic camming, and others. Two RS-232 ports make programming via touchpad or pc simple and straightforward. Communications capabilities include programmable controller, pc, or DeviceNet. While designing operational programs, built-in default ranges warn the programmer of errors. Hardware such as dual 32-bit RISC processors, flash ROM and NOVRAM memory, controller display, and all-digital electronics provide a cost-effective solution for simple motion applications.
Industrial Indexing Systems, 626 Fishers Run, Victor, NY 14564, FAX (716)924-2169.
Harmonic drive gear offers compact design
HD Systems Inc. has added a new zero-backlash harmonic drive gear to its SHF Series. The design offers a spacious through bore, yet is 40% shorter than its predecessor. The larger through bore makes more compact designs possible because wires, cables, or other shafts can pass directly through the center of the gear set. Its patented "S Tooth'' gear profile provides double the life and torque capacity of conventional harmonic drive gearing. Continuous output torques range from 5.4 to 745 Nm. Ratios from 50:1 to 160:1 provide positional accuracy better than 1.5 arc minutes.
HD Systems Inc., 89 Cabot Ct, Hauppage, NY 11788, FAX (516) 231-6803.
Microstepping motor fits in tight spaces
Phytron's 25.500 stepper motor fits into tight spaces. The 25-mm diameter motor has 500 full steps/rev for high resolution and accuracy. Holding torque is 10 or 20 mNm depending on the motor's length. Three different winding configurations are available for each length, and speeds up to 4,500 rpm are possible. Gearboxes can be eliminated in some applications, reducing wear, noise, and space. Microstepping provides even better accuracy. Applications include industry, research laboratories, and developing equipment.
Phytron Inc., 1345 Main St., Waltham, MA 02154, FAX (617) 647-3526.
Vibration can't shake this connector
This low-resistance connector is finding more applications in severe industrial environments. The re-designed Brad HarrisonTM Micro-ChangeTM connector averages less than five milliohm resistance on a pair of mated contacts. Gold-over-palladium/nickel plating improves conductivity, while an epoxy-coated coupling nut increases its corrosion resistance. The design is tested for submersion, power/temperature cycling, and humidity, and has a patented anti-vibration feature that prevents it from disengaging in severe dynamic or vibratory environments.
Daniel Woodhead Co., 3411 Woodhead Dr., Northbrook, IL 60062, FAX (860) 651-4708.
Circuits handle current surges
The ISP200/ISP300 are low-cost, high efficiency, 75V-dc, unregulated switching power supplies that deliver 2.0/4.0A of continuous current and 200/300W peak. Their circuits reportedly absorb and modulate the inductive current surges and maintain a more even power output. The ISP200 measures 3.9 x 4.0 x 1.5 inches and the ISP300 is 4.4 x 4.0 x 1.6 inches. Line voltage options include 120 or 240V ac, 50/60 Hz. The supply is protected against shorts, over-voltage, and over heating, and is priced at $149/$198 in unit quantities.
Intelligent Motion Systems, 370 North Main St., Marlborough, CT 06447 FAX (860) 295-6107.
NEWS FLASH
Piezo actuators isolate vibration
Harris Government Aerospace Systems Div. working with MIT engineers have integrated Polytec PI (Auburn, MA) piezo actuators into their active isolation fitting. The design maintains nanometer-level path length stability in the presence of vibration with a load cell set in the load path. A strain gauge and a pair of accelerometers mounted on either endof the strut provide force, position, and velocity information to the controller.
Vacuum-compatible motor has no magnetic fields
Anorad has codeveloped a piezo-ceramic linear motor (PCLM). It's constructed of select materials formulated for high vacuum compatibility. Designed to be mounted inside the vacuum chamber of the prototype ion-beam lithography system, the motor eliminates the intricate sealing system that is usually required for externally mounted drives. PCLM drives power the compact, vacuum-rated motor, devoid of intrinsic magnetic fields.
Control system meets government specs
The U.S government ap-proached Pacific Scientific to develop a control system for a test stand. It required a speed of 8,000 rpm; torque to 25.3 lb-ft rms, 108 lb-ft peak; and an acceleration of 266.7 rev/sec 2. Pac-Sci engineers chose their Pactorque(R) rare- earth motors and Millennium Drives(R). In-tegrating these components with PLC controls met the required specifications.