THINFILM
Figure 3. High performance, direct- drive scribing axis that is used with an
30
independent step axis (not shown) to form a high throughput, split- axis system
also important to minimize the turn-around time by quickly decelerating the payload and re- accelerating it to the full scan speed of 2.5 m/s.
One challenge when using linear motors is the issue of protecting them from process generated debris. This can be overcome by using creative mechanical designs that place the linear motor and bearing elements out of the direct path of falling debris. As an example, the design above places the linear motors so that they are protected by overhead horizontal structures that virtually eliminate exposure to processing debris.
When correctly applied, linear motor technology can provide dramatic throughput for scribing platforms. As an example, a top-tier solar panel manufacturer increased throughput by 300% using an Aerotech SolarScribe platform that utilized direct-drive linear motors. In a typical example, a single high-throughput scribing tool equipped with Aerotech linear motors replaces three or more standard scribing stations saving time, money, and manufacturing floor space.
Thermal Management
Because of the high accelerations and duty cycles, PV scribing applications require very high continuous currents in the linear-motor drive mechanism. These currents can generate a significant amount of heat that can affect both the accuracy and lifetime of the machine. To maximize the life of the motor when running in these conditions the system must incorporate thermal management techniques. A quick and efficient way to do this is to utilize air-cooled linear motor forcers that use a continuous stream of air over the coil to reduce its operating temperature.
In addition to active cooling of the motors, continuous temperature monitoring is also used. A
typical installation will include thermal sensing devices that are connected to the system controller to provide real- time motor temperature data. This information can also be used by the controller to shut the system down in the event that coil temperature becomes too high for safe operation. This helps to increase the life of the machine by providing failsafe operation and by providing the user with information that can be used to adjust the system parameters to optimize both the throughput and tool lifetime. Both active cooling and thermal sensing features support maximizing the life of the system.
Dynamic Performance
Beyond providing very high speeds and accelerations, the motion platform must provide good dynamic characteristics. Although all system geometric performance characteristics can be tested dynamically, PV panel-scribing applications are most concerned with scan-axis dynamic straightness and dynamic straightness repeatability.
Dynamic straightness and dynamic straightness repeatability show both the error motion that is transverse to the primary scan axis direction as well as the repeatability of that motion when scanning forward and reverse. The dynamic straightness number provides insight into what the form of the overall scribe lines will look like. This is an important parameter as this form will be repeated each time a scribe is made. Dynamic straightness repeatability will further quantify the amount of line-to- line variability or line parallelism across the panel. Dynamic straightness numbers are typically tens of microns with dynamic straightness repeatabilities less than 10 microns over a typical 1300 mm panel length. The key to providing this level of accuracy is to utilize high quality, precision machined components along with precision assembly methods. A well-versed motion partner will have the infrastructure as well as the experience to be successful in these areas.
Motion Controller
Another feature that is essential for increasing panel throughput and dynamic performance is the motion controller. Although most modern controllers can produce the basic trajectories
www.solar-pv-management.com Issue III 2010
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