Special gear design is at the heart of clear image in multi-axis tomography device.
For the rotational machines used to gather dental X-ray images, motion chatter can produce a fuzzy image, which is not suitable for diagnostic purposes.
Panoramic radiography is a branch of rotational tomography where the creation of images are through the movement of a source and receptor in such a way as to cause the foreground and background structures to blur, leaving a defined focal trough.
As a panoramic radiographic device, the Vantage Panoramic X-ray System, designed and manufactured by Progeny, Lincolnshire, IL, incorporates a DC X-ray source, CCD digital receptor, distributed processing circuitry, and an LCD touchscreen control panel for ease of use. What makes the Vantage system unique is that it is adjustable to the patient’s height via a motorized, 3-speed, telescoping column. The use of multiple lasers is to locate the patient and configure the device to the patient’s morphology. In addition, a workstation coordinates the individual processors.
The system incorporates an overhead, swing arm (lateral Y-axis) that supports a C-arm, which is the rotating member that moves around the patient’s head. The C-arm includes a tube-head, which produces the X-ray beam, and a removable CCD sensor, which is the digital image receptor. If this arm does not operate smoothly, a distorted image results.
The swing arm pivots on bearings located in the mounting casting fastened at the top of the column. Producing its motion is a ball screw drive, one end of which connects to the mounting casting and the other end to the swing arm. A step motor mounts at the column end. Both mechanical connections of the drive assembly are through ball bearing assemblies.
Suspension of the C-arm is on a pair of bearings mounted to the underside of the X-axis translation plate. The C-arm casting incorporates a 10" ID internal tooth ring gear that meshes with a pinion gear on a step motor mounted on the stationary X-axis translation plate. The motor is spring-mounted to maintain positive mesh and to minimize slop. The internal ring gear and pinion are sized and shaped to engage on the inside surface of the C-arm. With activation of the motor, the stationary pinion engages the teeth in the internal ring gear causing rotation of the C-arm.
The engineering team at Progeny worked with Intech to help design the C-arm casting and its interface with the gear drive for the C-arm’s rotation. Design of the company’s Power-Core products is specifically to reduce noise and vibration and run without lubrication, an important factor (a must) for medical equipment designers. Intech components are far lighter in weight than metal parts and offer longer life (less wear) and lower maintenance costs. Intech engineers used a proprietary gear load/life calculation to verify that the gears designed into the dimensionally restricted place would last at least 8,000 hours of operation or about 15 years in field use.
The challenge was to design a backlash free gear to produce a steady rotational movement of the image producing components. There was no room to employ the traditional split gear design. To eliminate backlash, installation of a spring, on slight angle relative to the axis connecting the gear centers attached to the pinion, pulls the pinion toward the 10" ID internal ring gear. The spring arrangement did eliminate the backlash, but caused the gear teeth to bottom out, resulting in chatter. The chatter registered on the X-ray image.
|The precision gearing for the Vantage Panoramic X-ray System uses Intech’s Power-Core nylon materials for reduced chatter, resulting in clearer images from the system.
Drawing on its expertise in gear design, Intech engineers designed and precision-machined the pinion and the internal gear to incorporate a special contact surface, which allowed the components to control the center-to-center distance between the inner tooth gear and the motor pinion. Adding the center-to-center distance management element presented a method for precise gear positioning in the mesh, and drastically reduced system vibration generated by the spring force and the resulting bottoming out of the gear teeth in the earlier design.
This configuration provides precise control over gear mesh vibration and backlash, resulting in high image quality in both a clockwise and counterclockwise rotation of the C-arm. It also adds a robust design element, which helps to increase product life so that image quality does not degrade with component wear and tear. With no fuzzy imaging due to chatter, dentists can make better diagnosis and provide better service to their customers.
Shown is the Vantage Panoramic X-ray system with the C-Arm that holds the lasers as well as the removable CCD receptor..
This article was featured in Today's Medical Developments magazine and can be viewed at http://www.onlinetmd.com/TMD-0912-motion.aspx
Lubricating a rack and pinion gear drive is often done manually. In industries, such as in food processing or packaging, where frequent washdowns are required, or where the gears are difficult to access, lubrication may be done only infrequently. Automated lubrication systems represent additional cost and require regular monitoring as they can clog up.
Intech Power-CoreTM gears do not require lubrication, reduce noise, and transmit motion with higher efficiency. The gears are precision machined from Intech’s Power-Core material with integral metal core for a secure shaft attachment. For wash down applications the core is available in stainless steel.
An important factor in designing today’s high speed machines is low inertia especially in systems where reversing motion is required. Intech Power-Core gears are up to 7x lighter compared to steel, absorb shock and vibration when movement in one direction is reversed, allowing higher machine speeds without sacrificing performance or wear life.
Intech engineers review each application and using a proprietary gear calculation, will advise the customer about the expected life of the gear. In many instances engineers are able to suggest design modification significantly improving the gear’s wear life. Intech rack and pinion gears can be found in bakery conveyors, position devices on packaging machines, cutting mechanisms on plastic bottle blow machines or on long gantry motion systems, to name a few.
Power-CoreTM gear for bakery conveyor system
To increase the capacity of their metal deposition furnaces with typically one cathode and one anode, we were approached by a metal refining company to design an electrically insulated gearbox that would rotate a multitude of electrodes suspended in a electrolyte solution. The design called for three stationary and one rotating cathodes and three rotating anodes. In the electrolytic process, exotic metal is transferred from the cathodes to the anodes and the rotating movement ensured an even deposition of the metallic particles.
The task was twofold, to rotate and electrically insulate in the gear box cathodes and anodes suspended in the electrolyte solution. Picture 1 shows the final solution. Intech engineers designed a planetary gear arrangement using Intech Power-Core™ gears with 316 stainless steel core, mating with a stainless steel sun gear. The drive gear was connected to one of the planetary gears. The electrodes are inserted through the extended, hollow gear hubs and clamped in place.
Picture 1) Intech Power-Core™ lower and upper plate (not shown) were used to anchor shafts with bearings and to electrically insulate them.
The electrical current is applied to the protruding electrical ends. To provide precise gear mashing and good gear life, precision SS bearings were pressed onto the hubs. While Power-Core gears have insulating properties, the electrical current could still escape through the hub/bearing/housing connection. To insulate the current, two Power-Core cover plates were precision machined to construct a housing for the gear box. The Power-Core gear box was then mounted on the metal cover of the furnace, see Picture 2.
Picture 2) Power-CoreTM electrically insulated gear box is mounted on the metal cover of the furnace.
In an earlier design, Picture 3 below, with a central drive and anodes and cathodes rotating, ceramic bearings were used to insulate the gear carrying plate. Using Power-Core plates and sealed SS bearings to anchor the gears in the gear box housing proved less costly and more reliable in the harsh conditions present in the electrolytic metal deposition environment.
Main electrical properties of Intech Power-Core™
- Volume resistivity at 10e10 to 10e14 (ohm.cm)
- Dielectric strength at 16-17kV/mm
- Dielectric constant of 4.0 (air dry), 50Hz)
Picture 3) In an earlier design ceramic bearings were used to insulate the gear carrying plate
One of our customers, who use an aggressive liquid bath in a plating process for coating metal parts, was experiencing a frequent breaking of the stainless steel chain drive which was corroding in the highly aggressive environment.
The parts are loaded into a large plating drum with a mesh exterior, which is then lowered into a tank containing a highly corrosive solution and heated to high temperatures between 120°F – 150°F. After coating, a series of cleaning and coating cycles are repeated across a battery of baths. A motor engages the drum drive, which needs to rotate slowly and steadily while carrying a high load into each step of the cleaning and coating process. The heavy metal parts in the drum can shift suddenly as the drum rotates, causing heavy shock load to be absorbed on the drive. The stainless steel chain, weakened by corrosion would give up under the shock load.
Intech engineers designed a large lubrication free Intech Power-Core™ gear and included a circular series of 2” diameter cast in ports made of Inconel™ in order to securely attach the gear to the drum. They also integrated a Power-Core bearing block in the shaft.
The Intech gear is resistant to the corrosive environment and was designed to absorb the sudden shock load, and proved to offer substantial savings to the customer.
When Dexter Magnetic Technologies introduced a dual axis robotic manipulator to control sputtering in the manufacturing of computer hard drives, it was an instant success that relied upon a sophisticated drive and pulley system that all too quickly developed a troublesome, excessive wear problem that was resolved with a solution presented by Intech Corporation.
Chris Ras, Product Development Manager at Dexter Magnetic Technologies, describes the drive system as “consisting of two single sided timing pulleys configured into two independent drive sections, each of which utilizes two single-sided timing belts.“ During tests at a customer’s plant, the faster of the two compact belt drives required frequent and precise tensioning to eliminate belt stretching and excessive wear.
Ras, in exploring a gear design as an alternative to the belt drive, contacted Tody Mihov, our Engineering Manager at Intech Corporation, to discuss how self-lubricating plastic Intech gears might work into his design. The application offered limited space, featured both high torque and reversing torque, and the gears needed to be retrofitted into existing equipment on location at the customer’s facility.
Upon reviewing load data using a proprietary gear calculation developed by Intech in conjunction with a leading university, Mihov determined that the Intech gear would work. He then decided to maximize the load carrying capacity of the Power-Core™ gears by applying an innovative Intech developed plus/plus gear mesh modification to the gear train. With the addition of two stainless steel drive gears, an Intech Power-Core™ idler gear that has an integral stainless steel core and a proprietary backlash-free plastic gear design, the desired smooth manipulator motion was assured. In addition, a special idler gear shaft was designed to provide an easy, field-ready retrofit.
An in-house test was constructed to determine how the Intech solution performed relative to visible wear patterns and drive efficiency. As per his expectation, Ras determined that drive efficiency increased by a full 15%! He reasoned that this was achieved in part by eliminating the radial stresses that belt tensioning transferred to the bearing. With the Intech Power-Core™ gears running stress-free, the only force transmitting onto the mating gear teeth was the torque, which traveled on a precision-machined pitch line.
With the retrofit Intech gear replacement system in place to manage reliability of the rotary axis, Dexter Magnetic Technologies has gained even greater industry attention.
Self-lubricating, Anti-backlash Gear Solution
One of our customers, who manufactures packaging machines for the pharmaceutical industry to produce caplets, sought to improve its competitive standing by eliminating the need to lubricate the 16” cast iron main drive gear and replacing it with a lubrication free Intech Power-Core™ gear.
Upon installation of the lubrication free Intech gear, the engineers ramped up the output to 600 caplets per minute (cpm), the industry standard, and discovered that there was no vibration previously experienced with the heavy cast iron gear. Encouraged by the performance of the low inertia Intech Power-Core™ gear, they increased the output to 700…800…, all the way to 1200 cpm. Even at this speed the machine was running smoothly and without vibration.
This was in contrast with all the previous experience using the cast iron gear which reached its critical RPM around 700 RPM, at which point the machine shook violently, and the reason why the output had been established at 600 cpm.
The customer settled on an output of 800 caplets/min as a standard for the company’s brand, a 25% increase over competitive machines. The first reward came shortly after introduction of the new machine. A company producing caplets used in automotive air bags sought to increase its capacity by 2400 caplets/min. Our customer was able to satisfy that demand with three machines that don’t require lubrication, where all its competitors quoted four machines that required constant lubrication and frequent shut down for maintenance.
Low inertia often becomes the dominant, albeit unexpected benefit of changing to self-lubricating Power-Core™ gears. The main drive in the DaVinci surgical robot is another good example.
A high frequency reciprocating gear and pinion being used in a feeder to insert postcards into magazines was suffering frequent breakdowns. Sealing the gearbox to permit lubrication that would prevent wear was not an option, and so Intech was approached to design a non-lubricated solution that could accommodate shock loads 5 to 10 times higher than the running torque of the application.
Intech Power-Core™ gears exhibit a high load sharing factor, an important quality when handling e-stops or shock loads. The load sharing factor, a measure of multiplying the load-bearing capacity of an individual tooth, is optimized for each application. Because the key way is cut into the metal hub and not the plastic, Power-Core eliminates the weak spot inherent in conventional plastic gears.
The metal hub absorbs all key way stresses, transferring maximum torque to the composite gear teeth. The teeth are made of a lightweight plastic composite, weighing just 0.037 pounds per cubic inch.
A non-lubricated plastic pinion replaced a metal gear, eliminating breakdowns in a high-speed card feeder.
Torque of Power-Core gear approximates that of cast iron, but without the brittleness, weight, lubrication, and teeth breakage. As a result, Power-Core gears can reach higher speeds, increasing the throughput of your equipment. We can precisely calculate torque capacity, allowing Power-Core gears to replace metal gears in many applications.
Power-Core gears can operate without lubrication at pitch line speeds up to 15 feet per second. When a special friction-reducing coating is added, you can double gear speed to 30 feet per second.
Power-Core™ gears have been used to upgrade the design of a latex dipping gear cassette assembly in a unique arrangement that replaces standard gears in order to meet critical performance and cleaning challenges.
The original gear box design resembled a tightly fitting cassette made with standard off-the-shelf gears. Unfortunately, as the latex material was being processed, the gears reacted with the latex material and expanded in size until the ceased turning. Cleaning required a complete disassembly of the cassette, followed by awkward and time-consuming hand scrubbing of individual components to yield less-than-satisfactory results.
In addition to requiring an easier cleaning process, the medical device manufacturer wanted longer wear-life and improved performance from the gears. Frequent cleaning and premature gear failure caused by gear swelling resulted in wear stress that resulted in system downtime and replacement on average every few months.
As part of a failure analysis, Intech provided an engineering design review that included a custom gear life calculation. Our engineering team recommended a system design modification to address performance uptime, improve wear life, and to create a user-friendly non-hazardous cleaning process.
The gear box modification design features custom Intech Power-Core™ gears with a larger pitch diameter, wider face width, and an integral stainless steel shaft that extends on each side of the gear and rotates directly within the load bearing cover plates. The open sandwich design, which can be seen in this image, allows for easy cleaning.
Compared to the previously used injection molded gears which vary in size due to internal stresses and moisture absorption, the precision machined Intech Power-Core™ gears provide consistent, smooth-running operation at reduced torque. Uniform Power-Core material will not distort or change size, so individual gears can be interchanged easily without matching pre-existing gears for a uniform fit, whereas injection molded gears had to be matched to other gears in order to function.
Intech Power-Core™ gears are machined from an inert, stress-free non-hygroscopic material with integral stainless steel shaft that offers outstanding performance where corrosion, abrasion, noise, lubrication, vibration, shock, and moisture create hostile operating environments.