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The Right Speed Reducer To Increase Your Robot's Efficiency

As energy prices heavily fluctuate and resources become more scarce, efforts have to be made towards the usage of renewable resources and reducing energy consumption, especially in industrial settings. The primary reason a manufacturer would consider a robot with higher efficiency in terms of energy losses, such as in the drive units, is cost savings. Often, enhancing the efficiency of current systems is more feasible than creating new methods to exploit renewable energy.

The challenge is enabling a higher energy efficiency without imposing significant compromises on load-carrying capacity, precision, component size, or noise levels. This article will explore why efficiency matters, compare speed reducer efficiency, specifically in delta robots, and discuss various strategies for enhancement.

 

Why Efficiency Matters in Robotic Applications

Efficiency is one of the most critical factors that engineers consider when designing and building machines. It is the ratio of the output power to the input power, usually expressed as a percentage, where power is the product of torque and speed.

This results in the following expression for efficiency:

Considering that efficiency is a factor of how much of the energy consumed is directly utilized in a useful manner in a system, the primary reason a manufacturer would consider a more efficient solution would be cost saving. But there is more to it than that:

  1. Reduced Costs: A more efficient robot consumes less energy to perform the same task. Over time, this can lead to significant savings in energy costs, especially in energy-intensive industries or applications.
  2. Longer Lifespan: Robots that operate more efficiently typically generate less heat and vibrations, and undergo less wear and tear. This can reduce downtime, extend the lifespan of the robot and reduce maintenance costs.
  3. Lower Footprint: With an increasing focus on sustainability and reducing carbon footprints, using energy-efficient robots can help companies meet their environmental goals and potentially qualify for green incentives or certifications.
  4. Improved Battery: Mobile robots can utilize the battery more efficiently, which leads either to a smaller battery or a longer run time.
  5. Human-Friendly Environment: More efficient systems produce less heat and noise, making them more suitable for use alongside humans.
  6. Better Control Performance: Decreased vibration and friction result in smoother motions, allowing for better control and repeatability.

Overall, while an energy-efficient robot may cost more upfront, the long-term savings in energy costs, increased productivity, and potential reductions in maintenance can make up for the price in the long run.

Factors Influencing Efficiency in Speed Reducers

A speed reducer, often known as a gearbox, drive or transmission, is an integral component in many machines. It transfers power from a motor to an output device, making it an ideal component to use for energy efficiency.

The efficiency of a speed reducer is influenced by various factors, including internal geometry, friction, lubrication, and load distribution. The design and materials used in the gearbox also have a significant impact on its efficiency. Internally, power is mainly lost due to friction between the internal moving parts (i.e. gear teeth), which can generate heat, vibrations or noise. The goal of a Mechanical Designer is to minimize friction losses while ensuring that the gearbox can transmit the required torque to the output device.

Ways to Increase Efficiency

Delta robots are parallel robots that are widely used in high-speed light-load pick-and-place applications, such as packaging, assembly, and inspection. They consist of three arms connected to a common base, which allows them to move in a three-dimensional dome-like space.

Delta robots require high-speed and high-precision movement, where a high amount of energy is lost to stop the robot in the braking phase. Instead of spending that energy in the braking resistor, the energy can be stored in a capacitor or fed to another motor through a DC bus. A higher speed reducer efficiency in this case would mean that more energy can be regenerated. High efficiency in delta robots leads to faster cycle times, higher accuracy, reduced energy consumption, and less wear and tear. Friction between the parts could cause vibrations, which greatly affects the precision of the operation. Specifically for uses in small component manufacturing, such as electrical chips, for example, precision is of the utmost importance.

The most popular choices of gearbox for delta robots are either planetary or strain wave gear. Planetary gearboxes bring higher efficiency and torque at the expense of complexity and precision, while harmonic versions offer high precision at the expense of efficiency. But what if there was a way to get the best of both worlds?

Efficiency in Delta Robots

There are different ways to increase efficiency in speed reducers, including reducing friction or altering the design. One way to reduce friction is by using high-quality bearings, which can reduce the amount of energy lost. Improving lubrication can also increase efficiency by reducing friction and wear. Using more efficient materials, such as ceramics and composites, can also improve efficiency by reducing weight and friction.

Altering the design of the speed reducer to reduce friction can also be a way to increase efficiency, albeit this requires much more time and resources. Efforts have been made to design gearboxes with better meshing parts, or with smooth surfaces, in an attempt to reduce or eliminate power loss due to the meshing of gear teeth.  

One application which can benefit from higher efficiency and where such changes are more easily implemented due to the straightforward design and low loads are delta robots.

The Archimedes Drive: A Highly Efficient and Precise Solution

The Archimedes Drive is a highly efficient speed reducer with over 85-95% efficiency. It uses a patented compound planetary traction system with smooth and hollow traction rollers. This design ensures that the speed reducer has low friction and high torque density, making it ideal for high-speed and high-precision applications, such as usage in delta robots.

The usage of traction rollers instead of traditional toothed gears results in the full elimination of backlash, as well as less wear and tear on the parts due to the continuous rolling tractive contact. Vibrations and noise are greatly minimized and more of the input power is translated into useful output movement.

In the Archimedes Drive, a small amount of output speed is “lost” due to creep in the traction rollers. This behavior differs from most speed reducer mechanisms, where friction causes most of the efficiency loss. Due to smooth rolling contacts in the Archimedes Drive, the friction losses are small and the ratio of the output torque to the input torque (or torque efficiency) is high. It has demonstrated efficiencies of up to 95% under full speed and full load conditions, with a high ratio in single-stage reductions.

Figure 1. Compound planetary traction system inside the Archimedes Drive

Comparing Different Types of Drive Technologies

There are different types of speed reducers, each with its efficiency-related advantages and disadvantages.

  • Spur gears are the simplest type of speed reducer, and they have a high efficiency ranging from 94% to 98%. However, they are noisy and not suitable for high-torque applications.
  • Helical speed reducers are less efficient than spur, with efficiency ranging from 92% to 96%. They are also quieter, smoother, and suitable for high torque applications, however, their precision is not very reliable due to slipping of the teeth.
  • Precision planetary gearboxes have high efficiency, ranging from 94% to 97%, and they are compact and can handle high torque. The downsides are they are expensive and complicated to manufacture.
  • Strain wave gear speed reducers have high precision and accuracy, but they come with lower efficiency, ranging from 70% to 80%.
  • An alternative solution would be to use a Direct Drive motor to directly drive the load, surpassing the need for a speed reducer. This motor has an overall efficiency level of 98%, but can only handle lower payload and requires a complex set-up between the motor and the load. Find a concise overview in Table 1 below.
TypeEfficiency (%)Accuracy (arc. min)Advantages
Precision Planetary94-971-10Compact, high torque, low backlash
Strain Wave Gear70-800.5-3High precision and accuracy, low backlash
Archimedes Drive85-950.2Zero backlash, extremely high accuracy, low noise
Figure 2. Comparison of accuracy and efficiency

Conclusion

Efficiency is critical in speed reducers, and it is essential to consider it when designing and building machines. The efficiency of a speed reducer is influenced by various factors, including gear tooth geometry, friction, lubrication, and load distribution. Different types of speed reducers have varying efficiencies, each with its trade-offs, be it complexity, precision, torque density etc. Delta robots require high efficiency to achieve high precision and speed, ensuring energy is not lost in friction or vibrations. The best way to achieve those requirements is to employ an Archimedes Drive, which can handle high speeds and extremely high precision, with over 90% efficiency thanks to its novel “compound planetary traction” design.

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