The handling of sample vials – in particular opening and closing – is a special challenge in the field of laboratory automation. The goal is to unite high levels of process reliability with minimal complexity. You’ll find out here which factors are important in finding the right solution.
The basic component is a rotary gripper unit which is combined with, for example, a 3D handling system. The point of departure for finding the right solution involves the dimensions of the sample vial and the required torque. Whether or not different vials will need to be handled is also decisive.
The sample vials themselves dictate the technical requirements. It has to be determined how much torque is required to open and close them. The amount of required torque should always be tested in advance with the vials which will be used later on – under conditions which are as realistic as possible. If the sample vials are manually filled the thread may be contaminated with, for example, glucose or salt-containing media. After the vial has been closed, the liquid dries out and become sticky or crystallizes. Considerably higher forces are required for opening in this case. If testing is conducted exclusively with brand new vials, one runs the risk of not making the technical requirements strict enough.
Force can be reduced significantly at the gripper if a positive-locking connection is used. On the other, friction-locked gripping necessitates much higher forces.
Torques of up to 5 Nm and gripping forces (depending on arrangement) of up to 200 N can be implemented with standard solutions from Festo. Other torques are available upon request.
The size of the vials
The necessary strokes can be determined on the basis of the height and diameter of the vials. In the case of vials of varying size, a larger gripper stroke is advantageous in addition to a longer Z stroke for the handling unit, in order to be able to fulfill all requirements with a single system if possible. This greatly reduces the complexity of the overall system.
Different thread pitches
When different sample vials are handled in a single application, not only can dimensions vary greatly in some case, the threads in the caps may differ as well. Simultaneous synchronization of rotation and stroke motion during opening and closing can be very complex, if it’s managed by means of software.
A mounting adapter with Z compensation was developed for Festo’s rotary gripper module EHMD for this reason. The adapter automatically compensates differences of up to 10 mm for cap thread pitch during opening and closing. Thanks to this simple mechanical solution with a passive slide, controlled motion for the Z-axis is unnecessary during rotation. There’s no need to program synchronization and the process sequence becomes significantly simpler.
Securing the vials
The file has to be held in place while the cap is being screwed on or off, in order to counteract closing or opening torque. A clamping unit or a second gripper, for example, can be used for this purpose, which can be adapted to different vial sizes by means of various strokes. Depending on the vials, simple positive locking with passive clamping may also be adequate.
When the cap is closed, two threads have to be aligned. It’s conceivable that the cap will be set onto the vial askew. Due to this misalignment, predefined closing torque is reached during tightening although the cap has not been correctly closed. In order to rule out this risk without expensive sensor technology, Festo integrates a “thread engagement step” into the process.
After the cap has been set onto the vial, it’s initially turned 360° counterclockwise with only slight pressure in order to align the threads on the cap and the vial. The cap is then tightened while monitoring the angle of rotation. Indirect torque testing is then conducted by means of a motor current measurement within a defined window. If no error messages are generated during the course of this process, the vial has most probably been reliably closed.
Decapping solutions from Festo
Alone the great number of different sample vials results in a large spectrum of technical requirements for automated opening and closing. Festo offers a broad range of solutions to this end as part of its compact handling systems – from complete rotary gripper modules to solutions comprising individual standard components, right on up to customer-specific new and further developments.
Rotary gripper module EHMD - for small sample vials
The EHMD is the most compact rotary gripper module in its class and is especially well-suited for opening and closing small sample vials like the ones used in HPLC applications.
The maximum torque value of 0.3 Nm is enough for opening vials with capacities of up to 15 ml. An optional module compensates for the cap’s thread pitch during rotary motion – for simple adaptation to a great variety of cap types and thread pitches.
The rotary gripper module is available in two versions: fully electric or with pneumatic gripper. Both permit infinite rotation.
Hybrid rotary/linear module DSL-16- ... -SA - for high torque
The DSL-16- ... -SA is ideally suited for applications which necessitate high torque values and gripping
forces. Vials with round throat and sealing cap or cover can be reliably and gently opened with the compact, thin module – with adjustable torque of up to 1.7 Nm. The combination consisting of pneumatic stroke and gripping motion with precisely adjustable and easy-to-monitor electric rotary motion makes sample handling reliable and reproducible.
Combination of EHPS and ERMO - for different requirements
Numerous different requirements can be fulfilled by combining electric standard gripper EHPS and electric rotary actuator ERMO. With the EHPS you can choose from amongst three types with different stroke lengths for small to medium-sized vials. The ERMO is available in four sizes – with maximum torques from 0.15 to 5 Nm. The rotary actuator is comprised of a mechanical system with permanently mounted motor and drive system (motor controller), integrated web browser technology and matching connecting cables.
Customer-specific developments - for specific challenges
A great variety of requirements can be covered cost-effectively, in extremely small spaces and with top-quality using standardized components from Festo. In the case of highly specific requests or challenges, Festo modifies existing products or develops entirely new solutions. The sooner we get involved in the planning process the greater the advantages are for the customer. For example, Festo USA developed an extremely compact solution for sample handling which was perfectly integrated into the customer’s system – with Festo standard components and a modified rotary gripper module. This approach resulted in minimal complexity with maximized productivity and process reliability.
About the author
Development Sample Handling LifeTech
Festo AG & Co. KG