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Case Studies
Harmonica Servo Drive Application
Elmo Motion Control’s Harmonica Digital Servo Drive
was integrated into an automated print inspection machine. Mounted in the optical head of the system, the Harmonica controls the
position of the camera as it scans the newly printed area. |
| The ChallengeThe printing industry has developed highly sophisticated
mechanisms to automate the various print processes. A complementary challenge has been to introduce automatic
process and quality controls in order to significantly reduce waste of time and materials when defects are found
– usually by the customer, after the printed material has already been delivered. Advanced Vision Technology
(AVT) Ltd. is a leader in developing sophisticated machine-vision technologies for inspecting printed substrates for both
random and process flaws. The company’s line of PrintVision machines enables printing personnel to automatically detect
and analyze defects as part of the printing process, alerting the print operator on-thespot in order to save valuable
time and wasted material. The AVT systems can be used with all types of continuous web printing (including labels),
and detect certain defects that are not always visible to the human eye, including color variation, misregistration,
streaks and mears. |
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| The Harmonica servo drive is compact and flexible enough to be mounted in the moving optical head of the inspection unit |
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| The actual vision
mechanism is a high resolution process control camera mounted
in the printing press apparatus. The optical head in the inspection
unit scans each millimeter of the printed material, back and
forth. When a defect is detected, the image of the printed area
is frozen on one of the two monitors of the control workstation
and an alarm is activated. The defect is marked and classified
immediately. At the same time, the inspector/operator is alerted
by a special beeper so that the problem can be analyzed and
fixed before a large amount of additional material is printed. The high-resolution
optical head operating in the inspection unit must be flexible
enough to operate with top accuracy, while the printing press
is operating at fast speeds. What is required is a highly responsive
drive that controls the position of the head, and yet is small
enough – in both weight and size – to be mounted within
the head without hindering the actual head motion. |
| Elmo's SolutionTo
meet the demanding requirements of the PrintVision system, AVT
installed Elmo Motion Control’s compact Harmonica digital
servo drive in the optical inspection head of the machine in
order to control the position of the camera. In this application
the Harmonica operates in position mode with RS-232 serial communication.The
drive’s small size and weight, as well as its programmability
(for internal scripts and homing)were the critical reasons for
devising this solution. Once the Harmonica was installed and
operating in the AVT machine,Elmo personnel suggested implementing
a CANopen network environment to further enhance the flexibility
of the application and extend the drive’s programming capabilities,
while at the same time reducing the complexity of the entire
machine. This option is currently being investigated. |
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AVT’s
Print Inspection Unit |
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| Compact Drive for
Top Accuracy and FlexibilityThe Elmo Harmonica
digital drive provided the ideal solution required for the high-resolution,
moving optical head in the print inspection mechanism. Easily
mounted and powerful in terms of its programming capabilities,
the Harmonica is managing all required position control of the
inspection camera. Furthermore, because the Harmonica could
be installed in the moving head, machine size and cabling were
greatly streamlined. |
| Harmonica
Digital Servo DriveThe Harmonica is a fully
digital servo drive that delivers up to 1 KW of continuous
power (and 2 KW of peak power) for DC brush, brushless
and linear motors. It can operate in current, velocity
or position modes and functions with a wide variety of
feedback options including Incremental Encoders, Resolvers,
Interpolated Analog (Sine/ Cosine) Encoders, tachometers
and potentiometers. The tiny drive packs one horsepower
into a 150 gram (5.3 oz) package. It features sinusoidal
vector control, trapezoidal vector control, trapezoidal
six-step and DC commutation methods. The Harmonica has
an auxiliary feedback port for ECAM, Follower, Dual Loop
and Pulse-and-Direction applications. Digital and analog
ports are also available. Integrated into the drive is
highly efficient power switching technology aligned with
Elmo’s especially fast implementation of CANopen
networking (DS-301/DS-402) protocol. One CANopen port
is installed along with one RS-232 serial port for communications.
The Harmonica is fully programmable with Elmo Motion Control’s
programming language (32 KB of memory is available for
storing programs). Using Elmo’s Composer setup tool,
Harmonica users can perform drive setup, configuration,
tuning, analysis and drive programming quickly and easily. |
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Harmonica Digital
Servo Drive
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