Modern biomedical, life science and diagnostic instruments rely on automated digital microscope technologies. DNA sequencers, cell imaging instruments, and digital pathology scanners are just a few of the many applications for digital microscopy solutions.
Dover Motion’s core strength is collaborating with our clients to understand their project and configure the right motion solution across X, Y, and Z axes to fit their unique application. When designing these complex systems, there are a lot of options to consider which involve tradeoffs in performance, throughput, and cost.
XYZ stages are a unique type of 3-axis linear translation stages which provide high precision linear motion in 3 degrees of freedom, including the XY stage for sample positioning and the Z stage for objective focusing.
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We have over 25 years of experience working with OEMs to optimize motion for objective focusing, and moving samples on a slides, well plates, or flow cells. Whether your project requires a customization to a standard product or a completely custom design, we’ll collaborate with your team to ensure to hit even the most challenging design, cost, and schedule targets.
Our engineers have developed unique motion control architectures for precision motion specifically tailored to the needs of OEMs developing microscope-based systems and instruments relying on optical imaging as the analytical detection technique.
When it is time to develop your next focusing instrument, consult with our motion industry experts to determine which of the latest technologies make the most sense for your application.
Determining the XYZ Motion Systems Architecture in an Automated Microscopy Instrument
Once the optical imaging elements are selected, the XYZ stage motion system architecture can be finalized. A typical field of view is much smaller than the sample being imaged. Thus, in order to image an entire sample, either the sample or the camera/objective will need to move along two perpendicular axes (XY). In addition, in order to properly resolve the image, the distance between the magnification objective and the camera (or image sensor) needs to be precisely adjusted. This is referred to as the Z axis. The Z axis is typically vertical and motion along it, to move the sample into the imaging field of view, occurs perpendicular to the XY plane.
There are three common configurations of the XYZ motion hardware. Selecting the best one depends upon the particular application’s complexities:
1.The XY stage moves the sample below a Z stage that is moving the objective or camera.
This is the most common configuration of XYZ stage motion. The benefit of this approach is that the image becomes stable after motion more quickly because it is only moving on one axis. This means it can be mounted to a sturdy structure instead of a stack of three moving axes whose resonances need to damp.
During sample loading, the objective can be moved vertically away from the sample mounting area, which makes changing samples easier. Also, Abbe errors are reduced because the overall stack is shorter.
XY stage moving slide with separate Z axis objective
2. Three motion axes move the object being imaged in X, Y and Z directions while the camera and objective remain stationary.
In this situation, the camera is very stable because it is mounted to a rigid surface. The drawback is that the travel required for the Z axis may be longer because the objective-to-imaging sensor distance is fixed. Typically, it requires less travel to move the objective with respect to the imaging sensor or camera.
3. The objective or camera is moved in X, Y and Z directions, while the sample remains fixed.
This approach works best when imaging small parts such as a microscope slide. As part size increases, the complexity of this approach also increases. Larger travels tend to require multi-axes to support a beam that has the vertical focus axis with both the imaging sensor and objective mounted to it.
Configuring the XY Stage and Z Axis
Determining the best motion technologies to configure the XY stage and Z axis depends on carefully considering the attributes of each in light of your requirements and budget. What focusing technology (software v. tracking laser autofocus) will you be using? What are your requirements for resolution, speed, accuracy and bandwidth? What frequency of images is required (do you require a single image per step or a continuous scan)? What are the size and shape of your samples and camera?
Please keep in mind though, that if the best technology still requires modification to suit your application, that is where Dover Motion excels. We have a track record of meeting focusing challenges at the edge of current capabilities in the industry.
Find out how Dover Motion’s combined solution for X, Y, and Z axes allowed NanoView Biosciences to improve the throughput and reliability in their next generation instrument. Check out our new video and case study to see how we helped NanoView Biosciences achieve all identified instrument improvement targets.
Additional XYZ Motion Resources
1. What are XYZ linear stages?
Linear motion stages provide precise automated positioning and are typically available as either single axis, an XY stage, or XYZ translation stages. Each axis of a linear stage must constrain the six degrees of freedom (X, Y, Z, roll, pitch, and yaw) of the payload to only one, producing translation along a straight line. This is accomplished with a set of linear bearing guideways which are attached to a base structural member that provides a stiff support.
- The linear bearing guideways can be implemented in a number of ways, including:
- Ball and crossed roller bearings
- Recirculating bearings
- Cam followers or vee wheels
- Air bearings
2. How do linear translation stages work?
Once the payload has been constrained to a single degree of freedom, the system’s next mission is to actuate the payload and provide precise incremental linear motion along the guideway.
Linear actuator methods include:
- Friction screws with anti-backlash nuts
- Ball screws
- Belt and pulley
- Rack and pinion
- Piezo actuators
- Linear motors
Using a linear motor is generally considered to be optimal for high speed motion systems and is the most precise and repeatable linear motion actuation technology.
A linear translation stage with a linear motor requires a linear feedback device as well as a servo drive and control to close a position feedback loop. With a high-resolution linear encoder, linear actuators can provide position control down to the nanometer level. A typical application for high precision linear actuators is to control the focus of a microscope objective in a digital imaging system.
3. What are the advantages of direct drive linear motor stages over piezos?
- Very high, nanometer-level resolution
- Very short move and settle times
- Ample travel compared to piezo/flexure stages
- High servo bandwidth, with a critically damped response
- Very high stiffness; no out-of-plane compliance typical in flexure stages
- Extremely long service life, with no need to vary servo tuning
4. What are the limitations of using Piezo Actuators within Z axis motion control?
A typical multi-axis imaging application involves a piezo stage moving an objective vertically for focusing with a separate sample motion using an XY stage. The use of piezo and flexure-based stages for XYZ focusing in this situation has many drawbacks.
Typically, a piezo stage can only move 100 – 300 nanometers. It moves very tiny amounts, very precisely; however, the initial steps of focusing often requires larger movements. The larger moves are necessary for avoiding objective collisions with the sample or for finding the optimal focusing plane due to sample variations. Because of their movement limitations, piezo stages may have difficulty accommodating thicker samples such as tissue samples.
Also, the XY stage motions or other vibration sources such as pumps and fans in the microscope or diagnostic instrument can impart off-axis forces on the flexure which results in instability of the piezo stage. The stiffness of a system is referred to as bandwidth, and piezo stages with flexures are typically lower bandwidth compared to a stage using a linear motor or screw combined with a crossed roller bearing.
Another drawback to piezo stages is that the advanced crystalline materials (PZT) used in piezoelectric motors are expensive to produce and frequently include lead and other potentially hazardous materials. Piezo controls are also costly and are frequently complex to operate.
5. How does a digital microscope work?
This automated digital microscope consists of a programmable high precision XYZ stage. This system does automated focusing, automated XY motion, and has a CCD camera replacing the human eye. The field of view of a microscope is typically very small. It can be a fraction of a millimeter to perhaps two millimeters, and, the sample is much larger. To overcome that, an automated microscope will take many pictures of the sample across the X and Y space of the slide. For more information, visit our Automated Imaging Page.
6. What is High Precision Motion Control?
Dover Motion can address the performance requirements of your most demanding applications, and has over five decades of experience designing precision linear stages, rotary stages, and complete precision motion control systems.
Our skillset in high-precision multi-axis motion control includes:
- Precision surface grinding, both pre- and post-hard coating
- The use of advanced materials such as alumina ceramics, carbon-fiber, Zerodur, and diamond-like carbon
- Structural exterior and interior light-weighting for maximum stiffness/mass ratio
- Skills in the use of cutting-edge position and angle metrology instrumentation
- 2-D and 3-D software compensation of residual stage errors
- In-house design of both ironless and iron-core linear servo motors
- Expertise in control theory and the design of high-performance servo loops
- In depth knowledge of precision motion control system design
High precision positioning stages serve a wide array of applications and can be considered “high precision” for various difference reasons. For some XYZ stages, it is critical to minimize geometric errors and provide true XYZ stage accuracy within the working area or volume. In other cases, one or more precision motion axes are required to move with exceptionally constant velocity. These systems often require that periodic triggers be generated at extremely precise positions, and that encoder cyclical error be eliminated.
In other applications, minimizing position jitter when stopped is paramount with permissible jitter being only a few nanometers. This requirement is often coupled with a need to move very quickly from position to position. For yet finer position stability, Coulomb friction can be engaged, reducing jitter to 10 to 20 picometers.
Dover Motion has extensive experience in providing precision motion control solutions configured to fit many different applications and can address even the most challenging requirements.