Laser Drilling Enables Advanced Drug Delivery Systems - Coherent

Recommendations

Info

Bowl Feeder Conveyor Presence Sensor Color Sensor Laser Drilling System Vision System Rejects Blow Off System Presence Sensor Color Sensor Inverter Laser Drilling System Vision System Rejects Blow Off System Collection Drum To begin the process, tablets are first introduced on to a single line conveyor from a bowl feeder. A color sensor views each tablet to determine which side is facing up. In the specific case of osmotic pumps, tablets typically are colored brown on the push layer side with a pink or yellow drug layer side. The hole thus needs to be drilled only in the yellow (or pink) side. Next, a presence sensor detects the passage of a tablet and then triggers the laser drilling process if the results from the color sensor were that the tablet was facing right side up. Tablets then pass through a machine vision inspection system. A digital image of each passing tablet is acquired and compared against the four possible outcomes, listed in the table. Two of these outcomes constitute a “pass” and two are considered a “reject.” Pass Reject Dilled and top side up Dilled and bottom side up Not drilled and bottom side up Not drilled and top side up Rejected tablets are removed from the conveyor by an air activated blow off system. Because of the speed at which the conveyor moves and the physical response time of the blow off system, the reject mode is activated as soon as a failed tablet is sensed by the vision system. This typically causes one or two tablets ahead of the rejected unit to be expelled as well. Then, the reject state is usually left on until the system sees five tablets in a row that meet either of the two pass criteria. An additional presence sensor downstream from the blow off verifies that no tablets are passing through the system when the reject condition is set to “on.” Despite the fact that some good tablets are rejected by this necessarily rigorous approach, the system still typically operates at 98% efficiency (tablets in/tablets out). Coherent Article for Pharmaceutical Manufacturing – – printed 01/18/07 Page 2
After transiting the first laser drilling station, tablets pass single file through an inverter, and then continue on the conveyor through a second laser drilling station. This second laser drilling station operates in exactly the same way as the first. Its function is to drill any tablets that were wrong side up when they passed through the first drilling station. Alternately, to drill both sides of a tablet, the color sensors in both stations are set to trigger the drilling process regardless of tablet orientation. Also, in that case, the vision inspection system is programmed to reject tablets only when no hole is detected. At the end of the line, processed tablets are fed into a collection drum, ready for final coating and printing. Laser Requirements Virtually any type of industrial laser can easily produce holes with the sizes and tolerances required for tablet drilling. Therefore, the primary selection criterion for the laser source is the throughput speed it can support. Secondary to this are considerations such as operating costs and uptime. The maximum achievable throughput speed for tablet drilling is influenced by several laser characteristics. For example, if all other factors are equal, throughput increases when using a laser whose output wavelength is well absorbed by the material to be processed. Also, high absorption in the processed material ensures that no significant laser power penetrates through to other layers in the delivery system, where it might cause damage. The organic materials used in drug delivery systems nearly all display strong absorption in the infrared, so the carbon dioxide (CO2) laser, with nominal output at a wavelength of 10.6 µm, is well matched for this task. In contrast, many organics are transparent at the near infrared output wavelength (1.06 µm) of industrial lasers based on Nd:YAG. From a practical standpoint, industrial CO2 lasers represent a very mature technology offering excellent reliability characteristics and low consumables costs. In fact, they offer lower overall cost per watt than any other type of industrial laser. Most organics are also strongly absorptive in the deep ultraviolet, and could therefore be processed using excimer lasers. However, the material removal mechanism in the ultraviolet is substantially different than in the visible and infrared. Specifically, visible and infrared lasers remove material in a thermal process. In contrast, deep ultraviolet lasers directly break interatomic bonds, atomizing the material in a process called photoablation. Generally, heating removes material much faster than photoablation, making the former method better suited for high speed tablet drilling. Photoablation is more advantageous in high precision applications, in which either the amount of material to be removed is small or processing speed is a secondary concern. Coherent Article for Pharmaceutical Manufacturing – – printed 01/18/07 Page 3
Page 1: Laser Drilling Enables Advanced Dru
Page 5 and 6: processing using galvanometer beam
Page 7: delivers processing capabilities no

Laser Drilling Enables Advanced Drug Delivery Systems - Coherent

Create successful ePaper yourself

Delete template?

Save as template?