The reader can operate in a number of modes from a presentation scanner to a triggered reader. The Read Cycle defines how it will operate. Setting up the read cycle type and parameters will involve a series of decisions based on your particular application:
The following two settings are common settings for all read cycle modes:
Look for # of symbols – This is the number of codes that the reader should find in each decode cycle. If the reader finds all codes, the decode cycle will pass. If it does not find all codes the cycle will fail an only the codes it finds will be output. The remaining codes will be listed as NOREAD. (This value can be set from 1 to 255, but 70 is typically a practical limit in an average complex scene).
Timeout after – This is the amount of time the reader is allowed to spend for the entire read cycle, acquiring and processing images until all codes are read. Users should set this value long enough to be able decode in all circumstances, but short enough to prevent camera from taking longer that the allowed cycle time of the production line. (20 msec to 65 seconds).
The different Read Cycle types are listed below.
In Presentation mode, the reader is in a continuous free running state. Parts can be presented to reader at will. During the cycle, the reader will continuously acquire and process images until all symbols are found or until the Timeout is reached. A Green Flash at the end of a cycle indicates a successful read.
The cycle time will include the Capture, Decode and Overhead Time and the Green Flash Duration.
In Continuous mode the reader is in a continuous free running state. Parts can be presented to reader at will. During the cycle, the reader will continuously acquire and process images until all symbols are found or until the Timeout is reached.
There is no Green Flash at the end of the cycle, so the cycle time is faster than Presentation mode.
In the various triggered modes, the read cycle starts with a trigger. The cycle will end and the reader will output data after decoding the expected number of codes, or after reaching the end of read cycle condition. The cycle time includes one or more Capture Times and Decode Times depending on the setup.
In all modes, the units are set respond to both Serial Triggers (through RS-232 or TCP), and to physical input triggers. The user is able to set the Serial Trigger characters. The physical trigger is typically set to Edge Based looking for a transition, but in some cases is Level Based, either high or low.
In all of the triggered modes, acquisition and image processing can occur in parallel. As images are acquired, they are put into a buffer pool. When processing is ready, it takes the image out of the buffer pool and analyzes it. This allows for faster overall processing.
It also allows for an initial burst mode where the reader can capture all required images from a fast moving part and then analyze each in turn as it has time. This is accomplished by setting the Delay Between Images to 0.
The size of the buffer pool is finite however (see note), so if all required images for the read cycle can not fit in the buffer pool, the Delay Between Images must be set to a value high enough so that processing can keep up with acquires (typically set to slightly longer than the average processing time).
Note: The maximum size of this buffer is dependent on the maximum image size in the system. It can contain 32 WVGA images before overrunning, six SXGA images, and two 5 MP images. If a WOI is used to get even smaller images, the maximum number of captures that can be contained in the buffer pool before over writing is 64.
This mode is useful in motion applications with slower line speeds or where symbol position or spacing may be random or not time-dependent. The read cycle starts with a trigger. Image captures are taken throughout the read cycle in a multi-buffered format (see diagram below). The reader begins processing the first captured image at the same time that it captures the second image. The reader will continuously acquire and process images until all symbols are found as the part moves by, until the timeout is reached, or until a new trigger is received.
Serial Trigger Character – Sets serial input trigger character. The reader will also respond to an Edge change on the physical trigger input.
Trigger Delay – This is the amount between when the trigger is received and when the unit will take the first picture. This is useful for adjusting code position on a moving line.
Capture Mode = Continuous – The reader will continuously acquire and process images. Acquisition and processing are overlapped.
Delay Between Images – This parameter is not used in continuous mode and is typically left at 0. The system will capture a small burst of initially, and then actively control the timing of subsequent acquisitions. This mode is guaranteed not overflow the image buffer pool.
Timed Rapid Capture is useful in fast-moving applications in which symbols are only in the field of view for a short time and precise timing is required to read all the codes. In this mode the read cycle starts with an initial trigger. During the cycle, the reader will continuously acquire new images based on the time interval and place them in a buffer. Each buffered image will be processed in turn until all symbols are found, all frames are processed, or until the Timeout is reached.
The acquisition timing can be set for a short burst to capture all images on a small or very fast moving part (Diagram A below), but is normally set to a longer interval to be able to catch all codes in larger parts, or slower moving lines (Diagram B below). Please refer to the Image Buffering and Pipeline Processing note above.
Serial Trigger Character – Sets serial input trigger character. The reader will also respond to an Edge change on the physical trigger input.
Trigger Delay – This is the amount between when the trigger is received and when the unit will take the first picture. This is useful for adjusting code position on a moving line.
Capture Mode = Rapid Capture – The reader will continuously acquire and process images. Acquisition and processing are overlapped.
Num Captures – This is set to number of captures required to see the codes after the initial trigger.
Rapid Capture Mode = Timed Capture – Reader will acquire images on a time basis.
Delay Between Images – 0 for burst mode. Set slightly longer than the processing time for normal operation.
Triggered Rapid Capture is useful in applications where each decode must be treated as a discrete event, regardless of symbol data. In this mode the read cycle starts with an initial trigger. During the cycle, the reader will continuously acquire new images based on subsequent triggers and place them in a buffer. Each buffered image will be processed in turn until all symbols are found, all frames are processed, or until the Timeout is reached. (See diagram.)
Each new trigger should be sent when the code is expected to be in the field of view. The trigger spacing should be set so the processing can keep up with the acquisition to not overrun and overwrite the buffer pool. Typically this is set slightly longer than the processing time.
In this mode, the reader will go into continuous read mode when the start trigger is received, and exit when the stop trigger is received or when timeout is reached. Even if the Timeout stops the cycle, the Stop trigger must be sent to completely close out the cycle. Data is output as soon as possible, but can be set to output only at end of read cycle through advanced parameters.
Serial Trigger Non-Delimited Off - When Serial Trigger is set to Off, the reader will respond to the IO trigger External Level. High will start the read cycle, low will end it.
Serial Trigger Non-Delimited On - When Serial Trigger is set to On, the reader will respond to Serial Triggers. It will also respond to the IO trigger External Level. By default, the start and stop characters are set to S and E.
Note: Start and Stop Characters cannot be the same.
Trigger Filter Duration (Leading/Trailing) – Amount of time the trigger must be present to be detected (debounce).
Serial Tigger Delimited – Sets if /IO or Serial Trigger and I/O mode are used.
Start/Stop Characters – Characters used for Serial Trigger.
This mode allows you a wider variety of read cycle scenarios, including Continuous Read Auto. Use this mode to select Trigger mode and to set Serial Trigger Character and Trigger Delay; to select Capture Mode and to set Number of Captures, Rapid Capture Mode, and Delay between Images; and to select the End Cycle On setting as well as Timeout and Number of Symbols.
Please see Appendix F of the MicroHAWK V320-F / V330-F / V420-F / V430-F User Manual for fuller explanation.
Note: The user can set up one of the modes described above, and then set the Cycle to Custom. This will show all of the exact setting for that mode.