Portable CMM Machine – Fixed or Portable?

Posted on Apr 27, 2021

Portable CMM machine

A coordinate measure machine is a substantial investment, and people are often faced with a decision between a portable CMM machine or a fixed CMM machine. Portable CMMs are especially prevailing in applications such as rapid prototyping, reverse engineering, and large-scale inspection of various sizes of parts.

What Is a CMM Machine?

A coordinate measuring machine (CMM) is used for measuring the geometry of products or physical objects by using a probe to detect whether there are discrete points on the surface or not. CMMs can be equipped with various kinds of probes, notably mechanical, laser, optical and white light. The position of the probe can either be manually controlled by an operator or controlled by a computer system.  

A coordinate measure machine is a substantial investment, and people are often faced with a decision between a portable CMM machine or a fixed CMM machine. As a matter of fact, there are quite a handful of things you need to consider to approach this. In this article, we’ll touch base on how to go about choosing between a portable unit and a stationary unit. 

What Is a Portable CMM Machine?

The key difference between the portable CMM machines and the traditional CMMs primarily lies in the measuring mechanism. While the traditional CMMs only use a probe to measure an object based on three Cartesian axes, portable CMMs adopt either articulated arms or an arm-free system that utilizes optical triangulation methods to enable greater freedom of movement around the object.

Portable CMMs with articulated arms have six or seven axes that are coupled with rotary encoders rather than linear axes. The articulate arms of the portable CMMs are light enough to be carried anywhere; one typically weighs less than 20 lbs. Though the previously less prevalent arm-free CMMs have become increasingly popular in the industries. They are equipped with compact linear or matrix array cameras and are even smaller and more portable than the CMMs with arms. Optical CMMs are also characterized by the no-wire design, enabling the measurement of all kinds of objects located virtually anywhere.

:: Read more: The Basics of CMM Measurement

Benefits and Limitations of Portable CMM Machine

Portable CMMs are especially prevailing in applications such as rapid prototyping, reverse engineering, and large-scale inspection of various sizes of parts. There are a great many advantages of a portable CMM, including the ease of use pertaining to taking accurate measurements in a controlled environment, and the flexibility in taking 3D measurements of a wide variety of parts in remote locations. Furthermore, portable CMMs are typically less expensive than their counterparts.  

One known downside of the portable CMMs is that they are required to be manually operated by at least one individual. In terms of accuracy, portable CMMs are deemed to be the inferior choice compared with other types of CMMs, such as bridge-type CMMs. And they also suffer from inadequate versatility as they are only suited for certain applications. 

Choosing Between a Portable and Fixed Unit

This is a common problem that bothers many because a CMM is considered one of the more expensive types of measuring unit. Before deciding which solution best suits you, it is advisable to address these questions first: 

1. What is the required level of accuracy?

2. What is the size of the part to be measured?

3. What are the requirements for the throughput?

● check the accuracy requirements

Simply put, knowing your inspection need, which is essentially embodied by the three questions, is the key to deciding whether you should opt for a portable or fixed unit. First and foremost, knowing the required level of accuracy will take more than the fundamental knowledge. You need to have a concrete understanding of the measurement parameters that you are working with. As with size capacity in a generic context, be mindful that the cost of a solution tends to increase when the accuracy also increases. If the accuracy requirement is right for your project, make sure that you have the needed budget to deliver.  

● consider what to measure

The next thing to do is to address the size of the parts to be measured pertaining to your inspection need. This includes the shape of the part while taking the volumetric into consideration. As aforementioned, the size capability of your inspection system is directly correlated with the cost that is later on incurred. So knowing whether your part is round, flat, irregularly shaped, etc. is very crucial for validating your inspection need. Generally speaking, a fixed CMM is ideal for projects that require taking the measurement of exceptionally larger parts in an automated manner. But this is also why fixed CMMs are typically more expensive than the portable counterpart. Don’t be surprised if you are offered a solution quoting over a million dollars for a bigger scale project.

● think about the total throughput

Moreover, you’ll need to consider the throughput requirements. If your project involves taking the measurement of a large volume of identical parts on a daily basis, a fixed CMM with the computer-controlled system may still be the more cost-effective choice. In other words, fixed CMMs with a certain degree of automation will be able to carry out high-volume, repeating inspection tasks a lot more efficiently with optimal cycle times. Conversely, if you do not have a tight accuracy requirement and a high-volume inspection need, a portable CMM may be the better investment. 

● other parameters to consider

Last but not least, with the core factors above address, there are other criteria of second importance you can take into account, such as the ease of operation, safety concerns, machine size, maintenance, and so on. The bottom line is that never make your decision based on the cost alone. Although you can keep the upfront cost down, having to live with a poor investment is the more dreadful thing.  

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