Seven Questions to Selecting a Measurement System

July 30, 2007
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A robotic measurement system (RMS) is made up of a noncontact sensor mounted to an industrial robot. Typically one sensor is used per robot, with systems including anywhere from one to six robots. In an RMS configuration, the industrial robot moves the sensor sequentially to each measurement location on the part. The sensor measures at each location and then the robot moves to the next measurement location. Source: Perceptron Inc.


Through the years, there have been many innovations in in-line, noncontact measurement, not the least of which is the variety of measurement system configuration options offered to customers. To be a world class, in-line, noncontact measurement supplier, a company must offer several combinations of configuration in order to meet a customer’s ever evolving process control needs.

In order to meet the very basic measurement system configuration requirements, customers must make sure that their in-line, noncontact measurement supplier or potential supplier can, at a minimum, offer the following measurement system configurations:

  • Robotic Measurement Systems (RMS). An RMS consists of a noncontact sensor mounted to an industrial robot. Typically one sensor is used per robot, with systems including anywhere from one to six robots. In an RMS configuration, the industrial robot moves the sensor sequentially to each measurement location on the part. The sensor measures at each location and then the robot moves to the next measurement location. In an effort to make the integration easier for the end customer, companies that deploy RMS should be able to use any brand of industrial robot. Robot independence allows customers to select a robot that they already use in their facility saving on training, maintenance and spare parts.

     

  • Multi Sensor Systems (MSS). A MSS includes structure-mounted noncontact sensors that can be placed at the end of a process or can be distributed throughout a process. The MSS uses noncontact sensors that fire in sequence or in unison, depending on the configuration, and can measure parts at a much higher rate than an RMS.

     

  • Hybrid Sensor Systems (HSS). An HSS is a combination of RMS and MSS in the same measurement station. This combination allows customers to measure common features with the MSS while taking advantage of the increased flexibility offered by RMS for the features that are not common.

    For all of the configurations listed, it is recommended that customers have the chosen supplier take the customers to see an active installation. A world-class in-line, noncontact measurement supplier should be able to provide valuable insight into the configuration selection process.

     



A multisensor system (MSS) includes structure-mounted noncontact sensors that can be placed at the end of a process or can be distributed throughout a process. The MSS uses noncontact sensors that fire in sequence or in unison, depending on the configuration. Source: Perceptron Inc.

Work Back from the Process

Each configuration of measurement system has a specific application to which it is best suited. For example, an RMS fits best when the customer has a high mix of vehicle models or parts, with little or no commonality, with lower production line rates and more cycle time for measurement.

MSS is best suited for applications that require a faster measurement speed for parts with more common features.

HSS is ideal if the part has a mix of common and unique measurement features, but there is insufficient measurement cycle time to measure all of the required features with an RMS.

In order to make the best possible system selection the customer must work actively with their in-line, noncontact measurement supplier, or potential suppliers, to answer the following questions:

  • How many different parts or vehicle models will be produced?
  • How much commonality is there between the parts or vehicles being produced?
  • How many parts or vehicles per hour will the manufacturing process produce?
  • How much of the manufacturing line cycle time will be allowed for measurement?
  • How many measurement features will be needed to adequately control the manufacturing process?
  • Will the parts or vehicles be changed frequently?
  • What is the primary goal for the use of the in-line, noncontact measurement system?
How many different parts or vehicle models will be produced? The number of parts or models that will be assembled on the production line in question will have a large impact on which system is best suited to measure the manufacturing process. The right combination of flexibility, measurement speed and cost will be greatly affected by part or model mix.

Typically, higher part or model numbers running down the same line will increase the need for measurement flexibility. However, high part or model mix can be achieved with high feature commonality, so high part or model count alone does not always mean the customer must use an RMS. High part or model mixes with high commonality between measurement features also could be effectively measured with MSS or HSS. Part and model mix alone is not enough information to pick an in-line, noncontact measurement system configuration.

How much commonality is there between the parts or vehicles being produced? Although part or model mix is an important criterion for system selection, the answer to the measurement feature commonality question will shed more light on a customer’s measurement needs.

In general, the lower the commonality between parts or models, the higher the need for a more flexible in-line measurement system. Higher commonality between parts or models allows for less flexibility in the configuration of the measurement system. Generally, high model mix with low commonality will be a strong candidate for an RMS. If there is a high model mix with high commonality, any of the three configurations mentioned could be recommended.

How many parts or vehicles per hour will the manufacturing process produce? How much of the manufacturing line cycle time will be allowed for measurement? An accurate answer to the line rate question will help to create a much clearer picture of which configuration to select for the measurement system. Higher line rates typically leave less time for measurement. High line rates and less measurement cycle time are more conducive to a MSS or HSS. Lower line rates and more measurement cycle time is a better fit for RMS.

How many measurement features will be needed to adequately control the manufacturing process?
The number of required features to be measured also will impact the overall measurement cycle time required. Measuring a large number of features requires more measurement cycle time. If there are a large number of features that need to be measured, the fastest measurement cycle will be with an MSS.

Will the parts or vehicles be changed frequently? Frequent changes to the parts or process also should be considered as a selection variable. Changing tooling on a frequent basis can be time consuming and costly. The higher the frequency of changes to the parts that are being measured, the better fit RMS will be for the customer’s process as changes to the measurement system require only programming and configuration changes and no new hardware.

What is the primary goal for the use of the in-line, noncontact measurement system? Customers can use their in-line, noncontact measurement systems for several purposes. Two of the most common ones are process control and containment.

Process control is the proactive use of measurement data to keep the process well maintained so that parts are built correctly. All three measurement system configurations are appropriate for process control.
Containment uses in-line, noncontact measurement systems to identify parts built out of specification. A system purchased primarily for containment must be able to measure every part on every cycle. If the number of features exceeds the measurement cycle time for an RMS, then a MSS or HSS should be investigated in order to meet the containment goal of the customer.

Hybrid sensor systems are a combination of robotic measurement systems and multisensor systems in the same measurement station. This combination allows customers to measure common features with the multisensor system while taking advantage of the increased flexibility offered by robotic measurement systems for the features that are not common. Source: Perceptron Inc.

Trade-Offs

Customers also must be aware of trade-offs associated with each type of measurement system configuration. Although RMS may be the most flexible, it also may be the most complex solution to operate and maintain.

Budget constraints must also be considered. Although all three configurations of in-line measurement system cost about the same amount when first installed, cost of ownership will vary greatly over the life cycle.

Other factors such as repeatability, accuracy and robot reach also need to be considered when picking an in-line, non-contact measurement configuration.

World class, in-line, noncontact measurement suppliers should be able to configure gaging systems that fully meet their customer’s needs. If both the supplier and the customer begin with a common understanding, the result of the selection process will most closely fit the requirements of the customer’s manufacturing process. Buying the best tool for the required job will benefit the customer for many years to come. Q

Tech Tips

  • A robotic measurement system is the best solution when the customer has a high mix of vehicle models or parts, with little or no commonality, with lower production line rates and more cycle time for measurement.

     

  • A multisensor system is best suited for applications that require a faster measurement speed for parts with more common features.

     

  • Hybrid sensor systems are ideal if the part has a mix of common and unique measurement features, but there is insufficient measurement cycle time to measure all of the required features with a robotic measurement system.

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