Why You Want to Know About Inertia Mismatch

Achieving lean manufacturing standards or increasing production is important for you. An automated system, like one that achieves packaging rates of up to 300 parts per minute, looks like the answer. Industrial automation is an engineering marvel.

For manufacturing companies, systems are becoming easier to operate. Yet, behind-the-scenes in the development and testing stages there are complex challenges to overcome.

High-speed systems depend on the synchronized interplay between parts. It's helpful to educate yourself and understand what specialists have to tackle. This understanding allows you to ask the right questions if you're going to invest in new equipment or upgrade.

Take a moment and read up on inertia mismatch.

The Problem

Have you seen the television commercial of a pickup truck pulling a jumbo jet along a runway? The focus is on the truck's power. However, this feat involves more than just power and torque. The coupling also plays a key role.

If the truck started off with a taut bungee cord connecting it with the jet, then the cord's elasticity contributes to inertia mismatch.

When a motor and a load are coupled together, the ratio of load inertia to motor inertia determines how well the motor can control the load during acceleration and deceleration.

A 1:1 ratio is theoretically perfect, but trying to achieve this ratio in the real world may not be possible. There are many rules of thumb for load to motor ratios but specific solutions depend on systems-level characteristics.

The topic is explored in-depth in the write-up Uncovering the Mysteries of Inertia Mismatch on the website motioncontrolonline.org.

The Role of Servo Motors and Axes

Reducing cycle times is important. Every second counts and saving time is one way you justify your investment.

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Let's say you have a six-axes robot, popular in industrial automation because it's easy to program and it's flexible in the types of tasks it can perform. It can handle loads from 5kg to 1000kg.

An operator starts up the robot and it swings into action. The movement is driven by servo-motors that produce motion in proportion to a signal received from a controller.

The regulated power comes from a computer that sends the signals and allows the arm to make precise movements. A servo-axes has a closed loop feedback so the properties of the drive signal can be tuned to optimize the performance of the axis.

The ratio of the load inertia to motor inertia affects the cycle times.

Tackling Inertia Mismatch

For robotics, acceleration and deceleration can be a time waster. A variance in speeds is common in flexible automation since the robots may be handling different size loads and not always performing at the same speed. That's a challenge manufacturers have to meet.

Let's say you want more power and speed in your equipment. Installing a bigger motor may be your first inclination, but that can work against you. The desired load and motor ratio is achieved through collaboration of cross-disciplines.

As stated in the Mysteries of Inertia Mismatch article, a best practice is for the mechanical design team to work with the electrical and controls engineers. A team can establish the parameters that will best serve the application.

Testing how motion affects the use of robotics is one way manufacturers develop solutions for customers. A qualified integrator and a manufacturer will help you understand the impact on your operation.

For links to expertise on this and other topics in industrial automation, continue to visit A3automate.org.

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