rom drug development through to medical diagnostics, automated liquid dispensing systems are vital. Handling small volumes
of liquid for purposes such as analysis or sample preparation, these machines rapidly deliver precise microliter (µl) quantities of liquid with a contamination-free approach. While each liquid dispensing system– including
its capability to handle specific types of liquid as well as its degree of automation – depends on end user requirements, these all rely on a coordinated motion system, responsible for aspirating, moving and dispensing the media with high throughput and repeatability. The liquid handling head comprises multiple channels, controlled by a multi-axis drive architecture. Two individual motors control movement of the channels in the X and Y directions via linear stages or belt systems, while individual channels move up and down along the Z axis, each driven by its own drive system. Each motor includes a gearhead and a servo controller per channel, coordinated by a higher-level motion controller or master PLC. The output of each motor is connected to a mechanical transmission specific to the OEM’s design, such as a timing belt, rack-and-pinion, or spindle drive. To aspirate and dispense the liquid, an additional drive controls the pipetting or syringe pump. This design is typically based on a motor-driven syringe or positive displacement pump, powered by a brushless DC (BLDC) motor, gearbox, and controller, commonly connected to a lead screw or ball screw mechanism.
Automated liquid dispensing systems often need to cover as many application requirements as possible while still achieving precision, throughput and robustness. For the OEM, this expands the market for each design while, for the end user, a machine with broader capabilities reduces the amount of equipment they need. When it comes to drive systemspecification,
high torque density will enable a compact design, allowing a configuration such as eight channels in parallel within a smaller pipetting head. To drive the pipetting channel in the Z direction, as well as the syringe pump, brushless DC (BLDC) motors are usually specified. By eliminating the physical brush–commutator
systeminherent to a brushed DC (direct current) motor, a BLDC design reduces mechanical losses, friction and heat generation, achieving greater
maxon ECX8 BLDC motor
torque density and enabling a smaller footprint. Motor design techniques such as optimised copper windings, high-quality magnetic materials, and advanced electronic commutation control, contribute to improved torque density and energy efficiency. An 8mm diameter
BLDC motor is commonly used to actuate the pump. This size motor is also used to
control channels with a 9mm grid spacing, while a 16mm motor
is required for 18mm pitch configurations. Combined with a BLDC motor, attention to
gearbox design can also improve torque density and efficiency with features such as low-friction bearings that reduce resistance under load and increase support for axial and radial forces, as well as usingmaterials that enhance thermal dissipation. To drive the syringe piston pump, the spindle can also be upgraded to ceramicmaterial rather than steel, which minimises friction – increasing efficiency and extending lifetime. Additionally, ceramics don’t require lubrication, reducing the contamination risk.
Overcoming forces such as friction also enables the motor to accelerate faster. The quicker an automated liquid dispensing machine can operate, the higher its throughput, which can be vital to reduce patient waiting times for diagnostic results or to increase productivity in laboratories. As well as offering higher torque, a BLDC
motor can operate at significantly higher rotational speeds (rpm) and achieve more dynamic bidirectional motion profiles, compared to its brushed counterpart. Although throughput is often important,
it must be matched with precise motion control, especially considering the dynamic nature of the system’s motion profile. While positional precision is important for controlling the pipetting head, it is critical for the pump, directly determining the dispensed volume. Every degree of variation in the plunger’s linear speed can causemeasurable deviation in the delivered volume. The greater the repeatability and reliability of dispensing, the faster the machine can safely operate, up to the limits of the motor–gearbox–lead screw combination. To control the pump, we usually specify a servo
position controller in combination with a high- resolution encoder, which directly determines plunger displacement and the resulting volume
Multi-channel liquid handling head
of liquid dispensed. With this system, repeatability can reach ±3 µm (micrometres) deviation across a typical operational lifetime of 10,000 hours. Although the motion requirements for the pipetting head are less stringent, a position controller is also specified here for consistent multi-axis coordination. To ensure long-term precision and
repeatability, mechanical design aspects must also be considered. For example, with a linear spindle drive system, axial play can develop over time due to wear. To prevent this andmaintain repeatability, a ceramic or preloaded ball screw can be used. Similarly, a gearbox design that minimises backlash, such as a strain wave, further improves precision and systemstability.
The ability to customise drive components and subassemblies is critical to achieving specific performance goals, and this is a requirement when working with automated liquid dispensing OEMs. The foundation of such collaboration is a clear understanding of the design objectives, such as repeatability targets, torque demands, or motion speed requirements. At this stage, it’s essential to fully assess the interaction between mechanical load, drive characteristics, and control dynamics, including feed force and cycle speed. This determines which parameters are fixed and which can be optimised. Typical areas of customisation for liquid dispensing machine design include motor winding adaptation to match available supply voltage and target speed, gear ratio selection, and lead screw pitch optimisation. To enhance system integration, it’s
advantageous to develop the drive solution as a complete electromechanical sub-system, including the motor, gearbox, encoder, controller, and transmission components such as the lead screw or
pulley.maxon can alsomanufacture a complete pipetting channel assembly based on the OEM’s design, with engineering refinements to make it lighter, stiffer, and easier to integrate. The influence of the drive systemon overall
liquid handling performance means that careful co-design and integration as a sub-assembly, or even as a complete cassette, is vital. Incorporating drive system engineering early in the design phase ensures all mechanical and control considerations are addressed, enabling faster time-to-market and improved systemefficiency.
31
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
