Gearhead Selection

Learn how to select the best gearhead for your application needs with Dr. Urs Kafader of the maxon academy

maxon’s Heavy Duty Drive Solution for Extremely Harsh Operating Conditions

maxon motor's Brushless 22mm HD motor and gear combo

maxon motor’s Brushless 22mm HD motor and gear combo

Brushless 22mm HD motor and gear combo

maxon motor launches its EC22 HD (Heavy Duty) motor, a 22mm-diameter brushless motor that outperforms any other commercial electric drive on shock, vibration and temperature tolerances. This motor was developed for the exceptionally high requirements in deep drilling technology and resists the most extreme operating conditions. Also available in combination with the GP22 heavy duty gearhead in 1 to 5 stages for use in oil or air operation.

As part of the motor’s development program, a high-temperature test facility was built, and extensive field trials were undertaken. The motor operated at temperatures up to 240°C and under atmospheric pressure conditions from high vacuum to 25,000 psi. It has also been proven to resist impulse and impact forces of 100G. It can operate while submerged in oil, trebling its 80W output rating to 240W because of the improved heat dissipation.

Although developed to perform critical downhole actuation functions, maxon believes the new motor will also appeal to other industries where reliability is essential. The motor’s efficiency of 88% in air (and above 70% in oil) makes it particularly suitable for battery-powered applications.

maxon 32 mm planetary gearhead for high radial loads.

maxon's 32 mm planetary gearhead for high radial loads.

maxon’s 32 mm planetary gearhead for high radial loads.

New design ensures smooth and true running.

maxon motor, the worldwide leader in high precision drives, has added two new gearheads to the already successful GP 32 program. Significant improvements have been made to the single-stage planetary gearhead: The planetary carrier has been reinforced, the bearings have been repositioned, and a ceramic version is now available.

With these new gearhead versions for high radial loads, maxon is now offering single-stage gearheads with extremely heavy-duty radial bearings. These versions are designed for applications such as toothed belt drives, applications that place enormous stress on the output stage due to the radial forces at work. The design of the GP 32 AR and GP 32 CR gearheads takes these forces into account. Both bearings of the output stage have been positioned as far apart as possible. As a result, radial forces of up to 140 N can be optimally compensated. The planetary carrier has been reinforced and given separate bearings. The axles of the planet gears are securely fixed in both halves of the planetary carrier. To achieve the maximum torque and life span, customers can select these axles in ceramic. The short-term permissible torque reaches up to 1.25 Nm.

The gearheads are available with output shafts in 6 mm and 8 mm diameters. These gearheads also feature smooth running and minimal fluctuation in friction characteristics. The planetary gearheads can be combined with various brushed, brushless, or flat motors in the maxon modular system.

For more information, visit our website at www.maxonmotorusa.com

Machine Optimization Through DC Motor Selection

Selecting the right DC motor is an important aspect of optimizing medical machine performance.

There are so many motors on the market today, from heavy-duty AC motors to tiny DC brushless and stepper motors. To use any of the motors users must have a full understanding of the application parameters, including power, speed, torque, physical size, efficiency, lifetime expectations, and other requirements. There have literally been books published about each of these aspects, and to define them all accurately in a short article would be difficult to say the least.

What this article will do is spell out the primary differences between DC brushed and brushless motors, what they can do, where they fit best, and how to decide which to use in your application. DC motors are being used in more and more industrial applications because of their flexibility and long life. Therefore, DC motor selection is often one of the most important steps in providing motion control of a medical machine, whether for prosthetics, medical tools, robotics, or medical training aids

Defining the Application

The medical market is unique in that most devices and machines are operated in a clean environment and around people as opposed to an industrial application. This means that long life and low noise (see Sidebar 1 on Maxon’s new low noise gearhead called the Koax Drive) are key characteristics the drives need to have in order to fit the requirements of many medical machines. DC motors are noted for their life-spans, particularly DC brushless motors which can last tens of thousands of hours in continuous operation, and much longer when operated intermittently.

Key criteria for selecting a DC motor for a medical machine application includes finding out what voltage is readily available for the application and what physical size the motor needs to be. Speed and torque can be determined once these two parameters are determined.

Voltage availability is a critical element in motor selection. Prosthetics, for example, are battery operated, while many rack-mounted devices and surgical tools operate from a 24 V power supply. DC motors are available for use at voltages as low as 1.5V and as high as 48V dependent on required power.

Physical size is often one of the limiting factors in motor selection for medical machines. Often a compromise needs to be made between which motor to use and the available space it needs to fit into. The prosthetics talked about earlier would need a small frame motor, while rack-mounted devices can be designed to accommodate larger devices.

Efficiency becomes a primary concern when you need to worry about power consumption to maximize battery life in a prosthetic hand or in a portable surgical tool like a drill or saw. Such concerns are not so evident in robotic machines used to perform many surgeries today.

As mentioned before, torque and speed also have an affect on motor frame size. High torque motors are often larger in size than their low-torque counterparts, which means that larger mounting hardware and larger housings may be a requirement of the machine. For example, it takes a larger motor to rotate the magnets in an MRI than it does to run the infusion pump for drug delivery. (See Sidebar 2 for more torque and speed information.)

Motor duty cycle could be one of the most telling aspects of a medical machine. Intermittent operation not only reduces the wear and tear on the motor and increases the life of the motor, but it also means that a smaller motor size can be used without depleting the positive characteristics of the machine itself.

Brush or Brushless

Key specifications quickly show that brushless motors last much longer than brushed motors, which rely on a mechanical connection for operation. And brushless motors run much faster as well. If you’re using a brushless motor for reliability, you won’t want to add a gearhead to the mix, though. The mechanical nature of a gearhead automatically means that it’ll have a shorter life cycle. Using a gearhead with a brushless motor will only negate the longevity of the combined system, and therefore reduce the longevity of the medical machine it was designed into. On the other hand, there are times when using a gearhead on a brushless motor is advised. For example, if the environment is such that noise is a concern or that a higher torque is needed, a gearhead will do the job very well.

Brushed motors would need a mechanical gearhead to increase speeds close to those of brushless motors. Using a gearhead with a brushed motor won’t change the life cycle to any great extent. Both are mechanical components that are subject to wear and tear. For medical machines, though, you don’t have to be concerned with dirt or grime mucking up the system. The cleanliness of the hospital allows you to get the most out of your mechanical components.

A real issue in selecting between a brushed and brushless motor is the expertise of the machine builder. Brushless motors either come with built in electronics or with external electronics to operate the motor. It takes some experience to provide the custom electronics many machine builders choose to provide. But for high sales volumes, the costs are easily regained.

Brushed motors, on the other hand, don’t need electronics to run the motor, offering a plug-and-play option to the designer. This means that if the machines are expected to sell in low quantities, a brushed motor will save on the overall cost of the system. A final concern is the power needed for the motors. Maxon motors are available in power ratings up to 250 Watts for brushed motors and 400 watts for brushless motors.

Overall, many medical machine builders are selecting to use brushless motors whenever possible. Long life and high speeds make these motors applicable to a broader array of applications. But as development costs increase and quantities decrease, brushed motors come to the rescue.

maxon's KD 32 Low Noise Gear

maxon's KD 32 Low Noise Gear

 Quiet Drives

The Koax-Drive, KD 32, manufactured by Maxon Precision Motor is a high-torque, but extremely quiet drive designed and manufactured specifically for medical technology (including surgical tools). The drive was designed to make handing instruments a more pleasant experience for users and patients alike.

The drive’s unique torque conversion system is a breakthrough for noise-sensitive environments, even under high loads. The KD 32 has a diameter of 32mm and a coaxial arrangement on the drive and output shaft that makes it ideal for use in applications where space is at a premium. 

maxon's DC Motor Torque / Speed Curve

maxon's DC Motor Torque / Speed Curve

Speed vs. Torque

Although speed and torque are independent requirements in many applications, typically speaking when the torque increases the speed will decrease – if the voltage stays the same. This connection is based on the slope of the speed/torque curve (called the speed/torque gradient), calculated using the formula below and shown in the sample curve shown here.

 Torque = {power [kw] • 30,000} / p • rotational speed [rpm]

For information:
maxon precision motors, Inc.
101 Waldron Road
Fall River, MA 02720
P: 508-677-0520
F: 508-677-0530
S: http://www.maxonmotorusa.com

Choosing the Right Drive Technology

Coming up with the right drive technology for your application often depends on the options before you. Here are five of the most common drive configurations being used today, along with their benefits and drawbacks.

Although there are a number of variations of drive technologies for motion applications, there are a few that are used for the majority of systems being built today. These most common drives do take a bit of understanding before applying, though.

Common among manufacturers are the application of gears to create flexibility in drive capabilities and characteristics. Gears come in a lot of shapes and configurations, including bevel gears, helical gears, worm gears, and the most common, the spur gear. The spur gear is also one of the simplest in form and simplest to implement. You’ll find spur gears used in everything from turbine plants to grinding mills, and from the medical equipment to construction machinery. When compared with other gear types, the spur gear offers high precision at both high speeds and with high loads. They are some of the most efficient gears on the market.

Maximum efficiency of a spur gear is approximately 90 percent per stage, which applies for loads that are typically one-half the rated torque (continuous torque) and greater, where it is essentially independent of the load. For some highly specific applications additional concerns may include a maximum rated load, maximum rated speed of rotation, and possible backlash. Temperature range can be a concern because special lubrication may be needed.

Planetary gears are also common among motion control systems. A planetary gear can provide movement with very low backlash, which is ideal for positioning systems used in the semiconductor and electronics packaging industries. These gear boxes are highly efficient as well, operating close to the 98 percentile even at low speeds. Some of the reasons planetary gearheads are used include their compact size and low weight, their low maintenance needs, and their design flexibility. One of the greatest reasons to use a planetary gear configuration is the fact that they are fully reversible while maintaining its efficiency.

Toothed belts are similar to gearheads in terms of their function. In comparison, they are smoother running and offer greater flexibility in the arrangement of the input and output shafts. Large pulley diameters with a correspondingly high reduction ratio and multiple drives can easily be realized. Further, toothed belts require no lubrication and little maintenance. Backlash can be kept small, although the elastic play is generally higher.

One of the drawbacks of using belt drives is that they are more sensitive to brief impact loads. Belt drives also have to be tensioned, and the resulting radial forces must be absorbed by an appropriate bearing design. In the operation of toothed belts electrostatic charging can also occur if the components are not properly grounded.

An interesting alternative to drive technology is the drive spindle, which transforms rotary motion into linear motion. The two most common designs include the recirculating ball screw and the threaded sliding spindle.

Threaded sliding spindles are characterized by high surface pressure, which means that positions can be maintained in vertical operation without a current supply. These are low-cost solutions, typically used as actuators. They provide smooth operation, but users must pay attention to the temperature of the nut, which means that operating time should only be up to about 60 percent of the duty cycle. Spindles are low efficiency devices (between 30 and 50 percent) to be run at maximum speeds of up to 0.7 meters per second. The suitability of threaded sliding spindle drives depends on the material pairing of the lead screw and the nut.

The other drive spindle configuration, the recirculating ball screw, provides linear motion through bearings that roll (or recirculate) between the nut and the guide grooves in the lead. The profile of the lead is rounded to improve the fit with the recirculation balls. The coefficient of rolling friction is approximately 0.02. These types of ball screws offer high repeatability when preloaded, and efficiencies near 99 percent. They also operate without running hot, which means that operating cycles with duty times to 100 percent can be realized.

The drawback of the recirculating ball screw is that they do not self-lock, which means that a holding break is usually needed. It is important to remember when applying threaded sliding spindles, that the value of the preload can have a significant influence on torque, friction, and operating life of the device. Some applications may need certain points verified, including the maximum loading of the spindle (including operating cycle and heating), maximum speeds of displacement, backlash (for positioning systems), and temperature ranges.

The drive systems mentioned here are a few of the most commonly used in the industry. Unless your application is highly specific, these drive technologies are the most cost effective and most readily available. Nonetheless, they must still be understood so that you get the necessary response to your needs. Always for special applications, it is wise to contact the supplier for the specific characteristics of the device you are attempting to use.

Type Efficiency Pros Cons
Spur High Parallel shafting. High speeds and loads. Can have back backlash, especially at low speeds or in a reversible situation. Low flexibility in input and output shaft configuration. Needs lubrication.
Planetary High Very low backlash. Compact size and low weight. Low maintenance. Fully reversible. More complex design. Higher cost than simple spur gearheads. Low flexibility in input and output shaft configuration. Needs lubrication.
Toothed Belts Medium Smoother running. Flexibility in arrangement of input and output shafts. Require no lubrication. Elastic play is high. Sensitive to impact loads. Must be tensioned (resulting radial forces must be absorbed through design). Open to electrostatic charges.
Threaded Sliding Spindle Low High surface pressure. Low cost. Smooth operation. Operates at 60 percent duty cycles. Speed limitations.
Recirculating Ball Screw Spindle High High repeatability (when preloaded). Operates at 100 percent duty cycles. Do not self-lock (needs a holding break). Be cautious of load values, maximum speeds, and temperature ranges.

For Information:
maxon precision motors, inc.
101 Waldron Road
Fall River, MA  02720
P: 508-677-0520
F: 508-677-0530
S: http://www.maxonmotorusa.com

Coaxial Drive KD 32 – Silent and Powerful

maxon's KD 32 (Koax Drive) - Low Noise Planetary Gearhead

maxon's KD 32 (Koax Drive) - Low Noise Planetary Gearhead

Low-noise planetary gearhead

The low noise coaxial-drive (Koaxdrive) KD 32 planetary gearhead from maxon motor is setting new standards in operating noise and torque levels. Measuring 32 mm in diameter and with a torque of 6.5 Nm, it is ideal for use in noise-sensitive, highly demanding applications.

The new Koaxdrive KD 32 combines the best of two proven gearing technologies, namely worm and planetary gearing. Special attention has been focused on the first gear stage, as this is where the greatest peripheral speeds occur and therefore noise. Our completely new, patent-protected design has enabled us to substantially reduce this noise. The worm-formed motor pinion drives the three offset planetary wheels interlocking with the internal gear which has straight cut teeth. The plastic planetary wheels are largely responsible for reducing noise levels.
All additional stages are set out as a completely “normal” straight-cut planetary gearhead. This unique torque conversion makes operation very quiet – even with high loads.

With an outer diameter of only 32 mm and a coaxial arrangement on the drive and output shaft, the Koaxdrive is designed for compact applications. A number of efficiency levels with the same reduction ratio increases the wide variety of applications. In the 11:1 to 1091:1 range, many reduction ratios are available as standard. maxon motor also offers high reduction ratios in one stage. A new, innovative coupling element is assembled on the motor side so that the motor shaft is not subjected to axial load. Input speeds of up to 8,000 RPM can easily be reached.

maxon’s modular system enables the Koaxdrive KD 32 to be assembled with various maxon motors. These low-noise combinations are ideal for hand tools and instruments that are used principally on or near patients in the medical technology sector.

%d bloggers like this: