Measurement List
Displacement sensors/measurement systems make many different types of measurements possible. Typically the application environment and the measurement target determines the type of measurement method that should be used for optimum results.
There are several types of measurement systems that you should become familiar with:
Dimension Measurement
- Thickness
- Width
- Height/Step
- Outer Diameter
- Angle
- Radius / Inner Diameter
Displacement Measurement
- Run-out/Vibration
- Eccentricity
- Stroke
- Positioning
- Edge Position
- Gap/Clearance
Profile Measurement
- Warpage and Flatness
- 2D Shape
- 3D Shape
Thickness
For those searching for Thickness Measurement Systems
If you’re searching for the best method of measuring thickness, the process may not be as simple as you may think. There are multiple factors that you need to take into account. These include first,the measuring system that will be employed during the measuring process and second, the shape and material of the object being measured. You’re going to need equipment that meets your needs sufficiently. Otherwise, you’ll just be flushing extra man-hours down the toilet during production. Therefore it’s crucial that you select the correct equipment the first time. (Read more about thickness measurement equipment.)
Measure Thickness in Sheet Form
When measuring the thickness of a target that is thin, such as a sheet, there are two steps you need to perform:
- Determine whether or not the item being measured is a thin sheet or another shape.
- Examine each of the methods that are outlined in each item to determine what the best measurement method is.
Here are a few sample applications:
Measurement 1: Thickness measurement of transparent films
When making a measurement, light is directed at a transparent object, and the light reflects from both the top and bottom surfaces. In this instance, you can measure thickness by examining the difference in location of where the light is reflected from in relation to the top and bottom surfaces.
Measurement 2: Thickness measurement of plastic sheets
The measurement of plastic sheets is performed by passing the target between two sensor heads. During the measurement process, sensors are positioned so that they are facing both the front and back of the target.
Measurement 3: Thickness measurement after roll press
This particular measurement is a bit more involved. The sensor heads used to make the measurement will be installed so that the surfaces on the top of the target and the roller are perceived as a single plane on the captured image. The thickness is found by performing a measurement that starts from the roller and ends at the top of the target.
Both the transparent and opaque targets can be measured for thickness. Because the thickness of a target is measured in reference to the roller, ensure that there is no clearance between the target and the roller.
Measurement 4: Thickness measurement of rubber sheets
In this instance, the thickness of a target is measured by its variance in height and its close proximityto the roller. Just like the previous example, both the transparent and opaque targets can be measured for thickness. Because the thickness of a target is measured in reference to the roller, make sure that there is no clearance between the two.
How to measure thickness (miscellaneous work pieces)
Here are a few sample applications:
Thickness measurement of coating films
If a transparent target has light directed at it, the light will be reflected from the top and bottom surfaces. When measuring thickness, calculate the difference in position of the light that was reflected from the top and bottom surfaces.
One question that you need to ask yourself is “does the displacement sensor have enough range to see both the top and bottom surfaces?” If the answer is no, it’s likely that you won’t have an accurate measurement.
Thickness measurement of sealing material
The thickness of sealing material is found by concurrently measuring both the target and base surface by using a 2D laser displacement sensor and measuring step from the profile that was obtained. An error can occur when there is a gap between the reference surface and the target.
Thickness measurement of wafers
A measurement is obtained by passing a target object between two sensor heads. The sensors used to measure the object are attached so that they face both the front and back of the target.
About optical-axis alignment
When a work piece is measured between two sensor heads, the determined thickness will remain the same. In other words, it won’t undergo any variations, even if the work piece vibrates during the measurement process. However, an error can occur if the optical axes of the two sensor heads aren’t aligned properly so that they’re not in a straight line. Now, if the work piece vibrates, bends, or moves in any form or fashion measurement errors may occur. The following instructions will guide you on how to correctly install the optical axes so that they are properly aligned.
The first rule of installation: Apply a massive amount of tension to the work piece. Weak tension can lead to disaster. If the tension isn’t high enough, the roll and the work piece will not come into full contact with each other. This can leave room for a gap that can range from a couple of centimeters to perhaps tens of micrometers in length. It’s recommended that when you perform a measurement that you use a tension of 50 N or more. You do have to factor in the tensile strength of the work piece being measured. During the measuring process, you should be in a location where the work piece tension will be as stable as possible.
Roller Eccentricity
Unfortunately, there will always be a rogue variable that will cause measurement errors. Roller eccentricity would be considered one of those rogue variables. Measurement errors may occur when a roller rotates due to the eccentricity of the roller. Here are a few tips on how to negate the effects of roller eccentricity.
1) When both edges of the work piece are utilized to measure thickness, you must measure both the surface of the work piece and the surface of the roller simultaneously. This will allow you to determine the thickness from the step value.
2) When using a roller as a reference when measuring a work piece on a roller, measurements can be made at an identical rotation thus canceling out the effects of eccentricity. This works even if the roller is moving around erratically.
Width
When searching for the best method to measure the width of a target, there are several key factors you need to keep in mind, including the installation environment, the shape of the target, and the type of measurement system. Selecting the wrong type of equipment that doesn’t meet your specific needs can lead to increased man hours during the production process as well as inaccurate precision while measuring.
Here are a few sample applications:
Width measurement of electrode foils
It only takes a single sensor head to measure a narrow target. This changes, however, when performing a measurement with two sensor heads. This is because two sensor heads are needed to perceive the left and the right edge positions of the target in question to determine its width.
Ultimately, it’s possible to obtain much higher precision measurements than with reflective measurement devices. Even hard to measure targets (such as transparent objects) can be measured in a stable manner.
Width measurement of elastomers
Width measurements and 2D cross-sectional area can be found much easier. Measuring elastomers can be convenient because even if a laser light cannot penetrate the width of a particular location, the object can still be measured because the measurement system is a reflective model. Even if the target moves to the left or right, an accurate measurement can still be obtained.
Width measurement of building material boards
In this instance, the width of an object is achieved by passing the target between two sensor heads. Keep in mind that the measurement spot must be smaller (regarding width) than the end face of the target.
Measuring Height/Step Height
Locating the Correct Solution for Height/Step Measurement
If you’re searching for the best method of measuring height or step height, the process may not be as simple as you may think. There are multiple factors that you need to take into account when measuring thickness. These include the type of measurement system being used, the installation environment, and the shape of the target. You’re going to need equipment that meets your needs sufficiently. Otherwise, you’ll just be flushing extra man-hours down the toilet during production. Therefore it’s crucial that you select the correct equipment the first time. Otherwise, you might be in for a world of headaches.
Solutions for height/step height
Here are a few sample applications:
Height measurement of dispensers
When measuring the height of a single point, you should use a reflective laser displacement sensor to get the most effective measurement. Multiple locations can be measured for height in the same instance by either scanning over the target with one sensor or communicating across multiple sensors.
Height measurement of connector terminals
A laser line indicates the profile of the surface being measured. Essentially, where the laser line hits a profile of the surface is obtained. This makes it possible to obtain measurements such as step height. Amazingly, it doesn’t matter whether or not the target is tilted. The step can still be measured accurately due to an alignment adjustment function in the sensor head.
Step measurement of electrode terminals
During the measurement of electrode terminals, two things occur. First, the silhouette of the target is projected. Then, the step height of two features (specified beforehand) is calculated. Similar to the case of the height measurement of connector terminals, step can still be measured accurately even if the shaft is tilted. This is due to the alignment adjustment feature. Also, the color of the target surface does not affect the measurement.
Height measurement of vehicles
When measuring the height of a vehicle, especially if it’s a single point, you must use a reflective laser displacement sensor. Multiple locations can be measured for height in the same instance by either scanning over the target with one sensor or communicating across multiple sensors.
Precautions during Height Measurement
More information about the tilt of the sensor head
Certain measurements have to be quite precise. The optical axis of the 2D displacement sensor must be perpendicular to the target being measured. Otherwise, a measurement error (caused by the angle) will occur in the step value. The larger the distance between the two points of measurement to determine the step, the greater the error. This is why tilt correction is used primarily when a step measurement is being performed.
Mirrored objects and transparent objects
Surfaces that have a mirrored or transparent surface require a bit of tweaking on the side of the sensor. In the occurrence that at least one target has a mirrored or transparent surface, the sensor head must be tilted at an angle that is at least half the angle of the projected and received light. Another important factor you must keep in mind that the head must have a single, dedicated use for objects with mirrored surfaces and transparent objects.
In addition, targets that are transparent must have a specific value to obtain accurate measurements. On the other hand, if the object is thin, there may be a lower measured value for the front surface height than is typical because of the effect of light reflecting from the back surface area of the transparent object.
There are a number of factors that need to be taken into account when determining the limit of the thickness of an object before affecting the accuracy of a measurement. These factors include the transparency of a target, the sensor head type, and the reflective status of the back surface. Before conducting any measurements, you should check with a manufacturer to obtain the most accurate information.
Measuring soft targets
Soft targets run into issues while being measured due to their inability to stay completely intact while they’re under heavy pressure. This is why when a soft target comes into contact with a probe. The target receives an indent thus causing a measurement error. What do you do then to measure targets that deform when touched (such as water)? A non-contact measurement provides the solution needed for such a situation. Because non-contact measurement doesn’t need to make physical contact with an object to obtain its measurement, the issue of indentation and the corresponding measurement error will no longer be a problem.
Measuring light targets
Understandably, the laws of physics play a significant role when it comes to measuring thin and light targets. In many cases, a light target has to be held down so that it does not float away (think of a piece of paper). If a light target is not stable, you will not be able to obtain an accurate measurement. When using the method of contact measurement, the probe presses down and holds the target surface in place. When this is done the stationary light object can now be naturally measured. This is the reason that the contact method should be used for this type of measurement as opposed to the non-contact method.
Measuring indentations
In most cases when you’re using a non-contact laser displacement sensor, the area being measured, which varies by range, is mainly smaller in size than the probes employed in the contact measurement process. Ultimately, this makes it capable of obtaining more accurate measurements while using the non-contact method.
Measuring Outer Diameter
When measuring outer diameter, there are many factors you have to take into account. These include the type of measurement system, the shape of the target being measured, and the environment where the object is being installed. Inadequate equipment will only lead to inaccurate measurements and wasted man hours during the production process. Choosing the correct equipment is key.
Here are a few sample applications:
Outer Diameter Measurement of high-speed wires
To measure this type of object, the target must be passed through a beam of collimated light. This is done to gauge the size of its shadow.
When measuring the outer diameter, you should select the measurement system that’s best suitable to the target diameter. In this manner, you’ll gain the highest precision measurements. In most cases the faster the sampling cycle, the more stable the measurement.
Outer diameter measurement of injectors at multiple points
To obtain this measurement, you’ll need the 2D optical projection method. This approach makes it possible to perform measurements of the outer diameter of various points. This includes the minimum and maximum values over a range that has been pre-specified. By using the position correction function, outer diameter can be measured accurately even if the target is tilted.
Outer diameter measurement of large steel pipes
The outer diameter of a target is measured by being placed between two sensor heads. It’s important to keep up certain functions of the sensor heads so that they’re able to operate at full capacity. Specifically, you want to ensure that the parallel alignment is working properly to inhibit values from changing if the target moves (typically to the left or right).
Angle
Angle Measurement Systems
When measuring an angle, there are always extra factors to consider which include the type of measurement system as well as the environment in which the system is being measured. As stated before, choosing the wrong type of equipment can lead to set backs due to imprecise measurements and increased man hours during the production process. Neither one of these scenarios is a good thing.
How to Measure Angle
Here are a few sample applications:
Angle measurement of bevel during welding
This process performs measurements by obtaining the cross-sectional shape of the location where the laser hits. At that point, the shape is used as a benchmark to measure the angle.
There are a couple of key points to take away from this section. First, angles can be computed internally. Second, angles can be measured by only one head.
Angle measurement of drill tips
Multiple specified points can be measured from the image that is acquired using the 2D optical projection method. Besides angle, other parameters can also be measured for multiple locations simultaneously. These include step, the outer diameter, and several more.
Measuring Radius (R) / Inner Diameter
Finding the right solution for radius measurements
There are a number of essential factors to take into consideration when trying to find the best method of measuring radius/inner diameter. These include the installation environments and the type of measurement system being used. When you use equipment that doesn’t fit your criteria not only do you lead to imprecise measurement, but also increased man hours during the production process. Utilizing the right kind of equipment is essential.
How to measure radius and inner diameter
Here are a few test applications:
Radius measurement of drum seaming
This object is measured by using a line laser that focuses on a target and irradiates it thus gaining a profile of the surface. This is then used to calculate radius.
Measurement radius can be measured directly without the need of calculating the estimated radius externally from individual point data. This is done by using 2D.
Inner diameter measurement of bearings
A measurement of the inner diameter can be made from the image attained using the 2D optical projection method. With the position correction function, the radius of a target will always be correctly measured even if the target shifts in place.
Inner diameter measurement of cylinder blocks
To measure the hole diameters of a cylinder block, the optical axes of two sensor heads must be bent at a 90-degree angle.
A key point to keep in mind is that the laser beams travel in a parallel manner. They pierce through the center of the hole and eventually cast a reflection upon the opposite inner walls. During this process, the rotation of the work piece can help to determine eccentricity and to measure roundness.
