Improve the Productivity of Robotics & Automation Systems with Lightweight Gears and Integrated Actuators By Alan Clements and Robert Mullins

Lightweight Harmonic Drive® Gears and Actuators Help Improve the Productivity of Factory Automation Systems fter sliding from its peak more than 25 years ago, U.S. manufacturing appears to be on the way back. More and more companies are deciding to make their products here, giving rise to a new buzzword in industry, reshoring, which represents the repatriation of manufacturing to North America from lower-wage nations. The reasons behind the renaissance in U.S. manufacturing are as diverse as the companies involved, but one key to the trend is worker productivity. As manufacturing employment declined...

Gear Characteristics Resulting Robot Performance Great Performance Fast Fast Acceleration Settling Time High Accuracy Excellent Repeatability Zero Backlash High Torsional Stiffness High Torque Density Smooth Trajectory High Payload Capacity Backlash, inherent in most gear technologies, makes it impossible to achieve this level of repeatability without using expensive high-resolution absolute encoders on the output of each axis. What then are the performance requirements for a gear or servo actuator to achieve high-performance automation? These requirements can be summarized as High Accuracy,...

Drive® motion control products incorporate this technology to produce lighter and more compact gear and servo actuator designs that enable robots to perform at their best. (See the sidebar Harmonic Gear Operating Principle to learn more about the technology used in Harmonic Drive products.) The majority of the world’s leading robot manufacturers use Harmonic Drive gears and actuators to take advantage of their superior performance including: • High Accuracy – Standard accuracy of Harmonic Drive gears is <1 arc-minute, but they are commonly manufactured with <30 arc-second accuracy per customer...

Harmonic Gear Operating Principle The harmonic gear principle of operation is both unique and simple. It is based upon non-rigid body mechanics and employs just three concentric parts to produce high mechanical advantage and high reduction ratios. Flexspline Wave Generator The Circular Spline Operating Principle Wave Generator The Wave Generator is a thin ball bearing fitted onto an elliptical hub. This is generally mounted onto the input or motor shaft. As the hub is rotated, a pair of moving waves is produced on the outside of the non-rotating outer race of the bearing. The Flexspline is a...

the velocity and position loops can be closed using a single encoder. Unlike other gearing, harmonic gears offer a high reduction ratio in a single stage. This helps reduce the size and weight of both the gear and motor. The high ratios available in Harmonic Drive® gears reduce the amount of output load inertia reflected back to the motor so the motor is able to respond quickly. The torque density of Harmonic Drive products is exceptionally high. This is a significant benefit when the gears are used on a robotic arm. The low weight of the gear reduces both the mass and inertia of the arm, allowing...

SHG-LW & SHF-LW SHG-LW and SHF-LW are compact hollow-shaft gearheads that are 20% lighter than standard SHF units. In addition to the hollow shaft feature, the gearhead incorporates a high-capacity cross roller bearing and an output flange to mount the load directly without the need for an additional support bearing. SHD-LW is a compact, lightweight, hollow shaft precision gear unit. The gearhead incorporates a Harmonic Drive® component set in an aluminum housing. It is 15% shorter and 30% to 40% lighter than the SHD-LW SHF series. It features a highcapacity cross roller bearing and flanged output...

Gears and Actuators in Action Harmonic Drive® gears and actuators are used in a wide range of applications, each of which takes advantage of a different characteristic of the gear technology. Some applications depend on zero backlash and high positional accuracy. Some require a high torque-to-weight ratio. Others depend on the unique configurations available. A few installations utilize all of these attributes. Industrial robotics is one of the major application areas for Harmonic Drive gear components. These applications require zero-backlash gears with high torque capacity, high torsional stiffness,...

Single-Stage, High-Reduction Ratio In the typical harmonic gear configuration, the Wave Generator is the input element, the Circular Spline is static, and the Flexspline is the output. When using this configuration the reduction ratio can be calculated from: Where: N f = Number of teeth of the Flexspline N c = Number of teeth of the Circular Spline The reduction ratio can be changed simply by changing the number of gear teeth on the Flexspline and Circular Spline. Gear ratios typically available include: 30:1, 50:1, 80:1, 100:1, 120:1, and 160:1. These ratios are offered in a single stage without...

design of these devices that serve people in need. Machine tool manufacturers often rely on Harmonic Drive products for their high-accuracy, compact form, and hollow shaft features. Common applications are in the fourth and fifth axes of milling heads for vertical machining centers and routers. Here, machine designers consistently use the hollow shaft to route wires to the spindle drive motor. Manufacturers of waterjet machines also use Harmonic Drive® gears and actuators for the linear axis and to compensate for the natural tapered cutting angle caused by dispersion of the waterjet stream. Harmonic...

Component Sets and Gearheads Harmonic Drive® products are divided into three basic categories: gear component sets, gearheads (gear units), and actuators. The features and form factors differ, but all provide the performance benefits and reliability for which Harmonic Drive is known. Component Sets are the core gear mechanisms used in Harmonic Drive products, and they offer the greatest design flexibility. Several component set product lines are available featuring different sizes, reduction ratios, and configurations, including ultra-flat and hollow shaft designs. This selection allows designers...