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Time-of-flight 3D camera technology provides multi-dimensional image solutions

Leveraging the benefits of Time-of-Flight camera technology in 3D machine vision applications

Overview
Time-of-flight cameras are a recent innovation made possible through improvements to semi-conductor technology and are a type of 3D range-imaging camera that use a collection of techniques to produce a multi-dimensional image showing the distance to points in a scene from a specific point. The subsequent image captured has pixel values which correspond to the distance, where brighter values mean shorter distances. These pixel values can then be translated into physical units of measurement.

How does a time-of-flight camera work?
Time-of-flight cameras capture 3D information by shining infrared light against an object and measuring the time delay between the emission and detection of the light. These cameras are similar to laser range scanners, except that the whole scene is captured simultaneously in real time and with no moving parts by an area scan sensor. Image acquisition is done without the usual need for scanning point-by-point as happens with a laser scanner, but, instead, the entire scene is captured with each light-pulse. This method of capture results in fast imaging and high lateral resolution combined with the depth information of the scene being grabbed.

Advantages of Time-of-Flight cameras
Simplicity Compared with other systems, the time-of-flight solution is very simple and compact, comprising no moving parts and with built-in illumination placed adjacent to the lens.
Efficiency Due to the ease with which distance information is extracted when using time-of-flight cameras, only a small amount of processing power is used.
Speed In contrast with laser scanners that move and measure point-by-point, time-of-flight cameras measure a complete scene with one shot with up to 100 frames-per-second making ToF cameras much faster then their laser alternatives.

Read more application-specific applications:
Case study #1 - Mesa SR 4000 Time-of-Flight cameras in logistics
Case study #2 - Mesa SR4000 Time-of-Flight camera in security/area control


While Time-of-Flight cameras, have decided advantages over other forms of image capture for certain applications, users should be aware of factors that, unless managed, might compromise the camera’s output.
Areas of caution
Environment The degree of the object's reflective properties, colour, gloss and complexity of the scene has considerable effects on the accuracy and co ToF cameras output a confidence map with each 3D map
Background light Background light, whether artificial or sunlight, while being suppressed, may need additional management. However modern ToF cameras are overcoming these issues with more advanced designs
Multiple reflections Unlike laser scanning systems, ToF cameras illuminate an entire scene. Due to multiple reflections, the light may reach the objects along several paths, consequently care should be taken with multiple path reflections.
Interference If several ToF cameras are running at the same time, each may disturb each others' measurements. However, there are simple fixes for this situation

Applications for Time-of-Flight Cameras
Optimised for use in industrial applications, a time-of-flight camera can be deployed in a range of environments:

Machine Vision
More general machine vision applications require highly stable and reliable sensory systems. ToF cameras provide a reliable set of depth data, increasing the robustness and flexibility of many surveillance, inspection and logistics systems

Robotics

The ability of technology to mimic the complexity of human eyes, in real time, has been anticipated for some time. TOF cameras overcome the problems of alternative robotic vision solutions such as stereoscopic cameras or laser scanners which are bulky and don’t always provide accurate information. A single ToF camera allows a single compact sensor to serve as a highly capable input device in many robotic applications such as:
• Autonomously guided vehicles, with improved obstacle identification and avoidance, for map building, localization, and path planning.
• Service robots in both industrial and consumer applications.
• Industrial robots in assembly, quality control monitoring, material handling, bin picking and automation

Security / Surveillance
Segmentation of 2D images is highly dependent on illumination conditions and is difficult to achieve in many cases. The third dimension that is delivered by a ToF camera allows for much easier segmentation of images. This allows, for example, determining the presence, location, and number of persons or objects in a target zone and to address efficiently the following applications in the field of security and surveillance:
• Person-counting at secured gates for detection of tail-gating or undesired intrusions.
• Person-counting at airports and in mass-transit systems for security or statistical purposes.
• Object surveillance or detection in sensitive areas.

Medical / Biometrics
The ability of the ToF camera to provide immediate, cost-effective images enables a diverse set of emerging medical and biometric applications, including:
• Human-machine interface for geriatric rehabilitation computer games.
• Clinical use of ToF for patient-position and patient-movement monitoring to increase the effectiveness of various therapy systems including radio-surgery.
• Laproscopic surgeons being provided with surface dimensions to assist in endoscopic surgery procedures, enabling the marriage of the real-time image to previously-generated scanned images


CASE STUDY #1: ToF cameras in logistics
The challenge: Pick-up of pallets in automated warehouses

Today’s warehouses are highly automated in order to increase the throughput capacity and reduce both transit times and the number of staff.

Conventional, manually operated forklifts are replaced by automatic guided vehicles (AGVs), which are controlled by the warehouse management system and typically travel on pre-defined routes using markers for positioning and navigation.

It remains a significant challenge for AGVs to pick up pallets with reliability as, even though the location of a pallet is well-known, the exact coordinates to which the fork must be moved to pick up the pallet are not known with sufficient accuracy. Therefore, a sensor is needed to detect the pallet and locate the exact position of the slots or pockets into which
the forks are to be inserted. (Figure, right, shows the position of the camera in red).

The solution (deploying a MESA SR4000 Swiss Ranger camera)
The automatic pallet pick-up is enabled by a ToF camera from MESA Imaging. The camera captures a 3D image that is analyzed to detect the exact position of the fork pockets of the pallet. The camera is installed on the front portion of an AGV and communicates via its Ethernet interface with the control unit of the vehicle.

The advantages of ToF cameras in logistics
Compared to alternative technologies, a TOF camera offers some key advantages: It can scan an area in a single exposure within a fraction of a second and achieve frame rates of up to 100 per second. Laser line scanners, in contrast, only scan one line at a time and they must be mechanically panned or translated to scan an area. Moreover, a TOF camera does not rely on any complex image processing to acquire distance information. In this respect it has a key advantage over a stereo vision system, where features in the left and right image must be matched to compute the distance information. This can result in long latency times, or in an incomplete depth map for image regions where no matching is possible.

TOF cameras directly measure the distance for every pixel, the depth map is, therefore, always complete and the latency time is very low.

Finally, an important advantage of TOF cameras is their ability to handle varying light conditions and the fact that no image contrast is needed to detect the fork pockets. This allows reliable detection in challenging situations, e.g. in the presence of shadows, or when pallets are dirty or damaged.

Key benefits of using the Mesa SR 4000 in logistics deployments
Reliability Very reliable fork pocket detection, eliminating need for operator maintenance or trouble shooting and minimizing down time of the system
Speedy detection Very fast detection for short cycle times and maximum vehicle efficiency
Robustness System can handle varying ambient light conditions, and is not troubled by shadows. Reliable detection of dirty or damaged pallets.
Small size With just 70x70x70mm easy to integrate in existing fork lift setup
Flexibility Communication via Ethernet interface, platform independent, compatible with any operating system
Value-adding 3D data from the camera can be used as complementary purposes, including safety, collision avoidance, and navigation


CASE STUDY #2: ToF cameras in high-security access control systems
The challenge: Securing corporate protection against criminal or terrorist activities in highly-sensitive areas
High security access control systems typically consist of an airlock, i.e. a small room with 2 doors, where only one door can be opened at a time.

In order to access a secured area, an authorized person enters the airlock through the first door and is then identified by means of biometric sensor, an RFID tag, etc. Once the system has verified the person’s identity and access permission, the second door is unlocked, and the person can enter into the secured area.

A significant challenge for access control systems is to detect when an unauthorized person tries to enter the secured area together with an authorized person, a so-called tailgating situation (see figure below). Such a situation is very difficult to detect with a conventional security camera. The situation even more complex, when the person entering the secure area may carry an object such as a briefcase or backpack). The system then needs to be able to differentiate between people and various objects.

The solution
(deploying a MESA SR4000 Swiss Ranger camera)
The solution consists of using a single camera mounted on the ceiling of the airlock (see figure right, above). The wide-angle objective allows reliable, 24/7 monitoring of a large area even when the room height is a constraint. With its compact size, discretion is assured and nor does the camera impact on the structural design of the airlock. (Figure, right, shows the position of the camera in red).

The camera communicates with the door controller unit via its Ethernet interface. Image processing can be carried out in the door controller or, as in the case of the Mesa SR 4000, in the camera itself on its embedded processor.

The advantages of ToF cameras compared with conventional security cameras
Compared to conventional security cameras that only see 2D contours of an object, a ToF camera can sense the 3D shape, enabling very robust detection of persons and objects, making it much more difficult to deceive the system.

Compared to stereo vision systems, a ToF camera needs no matching of image features, and 3D data is available for every pixel in every frame in real time at up to 50 frames-per-second (when using the Mesa SR 4000) and with very low latency. Furthermore, TOF cameras do not suffer from occlusion.

ToF cameras are active imaging systems in illumination. They are; therefore, not sensitive to variations in ambient light conditions and can even work complete darkness.

How the 3D ToF camera sees and reports tailgating    

Black-and-white, low contrast image shows a normal (left) and tailgating (right) situation

The same situation using a colour-depth image

Key benefits of using the Mesa SR 4000 in security/surveillance operations
Accuracy Very good detection accuracy of tailgating situations meeting highest security requirements
Flexibility Senses 3D shape of object, data quality allows differentiation between persons and objects
Robustness No image contrast required and there is no issue with varying ambient light conditions or shadows
Compactness Very compact device which is easy to integrate causing minimal impact on structural design of room
Simplicity of use Easy mechanical and electrical integration with embedded image-processing capability

 

Click here to learn more about the Mesa Time-of-Flight camera available through Adept Turnkey

Adept Electronic Solutions are "The Machine Vision and Imaging Specialists" and distributor of Mesa Imaging TOF products in Australia and New Zealand. To find out more about any Mesa Imaging TOF products please email us at: info@adeptturnkey.com.au or call us at Perth (08) 92425411 / Sydney (02) 99792599 / Melbourne (03) 95555621 or use our online contact us page.

 

 

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