Motorized Stages & Others -CHUO PRECISION INDUSTRIAL CO.,LTD.-

Motorized Stages & Others

Types/Mechanisms/Guidance Method

■Types/Mechanisms/Guidance Method

Comparison Chart of Guidance Methods
V-Gap and Cross-Roller (HG-VCR Method)
V-Gap and Cross-Roller (V-CR Method)
V-Gap Rail and Steel Ball (VB Method)
Roller-Way
Ball-Way
Ball-Bushing
Rotary Bearing

■ Tilt Stage Drive Mechanisms

An Overview of the Complex Coupling Mechanism
Issues with Conventional Technology
Features of the Complex Coupling Mechanism
Positioning Errors
Patents
The Tilt Stage V-B Method Guide Rail

Comparison Chart of Guidance Methods

Guidance Method	Movement Accuracy	Load Capacity	Rigidity
V-Gap and Cross-Roller (HG-VCR Method)	☆	☆	☆
V-Gap and Cross-Roller (V-CR Method)	◎	◎	◎
V-Gap Rail and Steel Ball (VB Method)	◎	○	○
Roller-Way	◎	◎	◎
Ball-Way	○	○	◎
Ball-Bushing	△	△	△
Rotary Bearing	◎	○	○

Table 1 Guidance method comparison. ☆: Superior　　◎: Great　　○: Good　　△: Possible

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V-Gap and Cross-Roller (HG-VCR Method)

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Our original guidance method which is developed aiming at further performance improvement of V-CR method.
This method is named “HG-VCR”.
Rollers are retained with the retainer by making interval of arrays between the rollers as narrow as possible and increasing the number of arrows. High pre-load can be imposed to it. It is compact in size and has high stiffness.
It was adapted to our new Auto and Manual Stages, and can support not only precise positioning of various sensors and cameras but also precise positioning and measurement of various production machinery and inspection equipment.
In addition, since it has stiffness, it can be used at ease even for the applications where certain degree of unbalanced load is imposed.

We have applied for a patent for this “HG-VCR”.
Patent Application No.: 2006-070036

V-Gap and Cross-Roller (V-CR Method)

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Two mutually-facing V-gap rails contain rollers that crisscross each other at a 90° angle to make up one set. It is designed so that two sets are used together.
After being quench hardened, the V-gap rail orbital plane has been ground to high precision to allow an extremely high level of straightness.
The use of rollers allows a large load carrying capacity in both the horizontal and vertical directions. This method is perfect for applications that require a heavy duty stage with high precision.
Tilt Stage Drive Mechanisms
We have a new lineup of products that uses a brand new drive mechanism for tilt stages that are used in a wide variety of fields that require angle adjustment such as optical pickup adjusting devices or disc manufacturing equipment.
This new drive mechanism is our independently developed “Complex Coupling Mechanism CCM” that can resolve many of the traditional issues with tilt stages and allows improved precision, high resolution, durability, and driving torque.

V-gap Rail and Steel Balls (VB Method) Straight Movement Type

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Two mutually-facing V-gap rails contain the steel balls arranged in line to make up one set. It is designed so that two sets are used together.
This method is used for applications that require a tilt stage with high precision and light load.

V-gap Rail and Steel Balls (VB Method) Curve Movement Type

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Unlike the straight movement stage, the V-gap rail describes an arc.
For this, if the guide rail of which structure is same as that of the straight movement stage, then displacement occurs between the V-gap and the steel balls, and abnormal pressure is imposed to the V-gap.
This will cause decreased durability as well as the retainer (The part which consists of the steel balls and the plates putting the balls between them) will be displaced and no longer function.
In order to solve this problem, we developed a new type of guide rail with quite new ideas.
In this guide rail, orbital distance is corrected inside and outside the arc at 4 points to which the steel balls are contacting to prevent deteriorated durability and decrease displacement of the retainer extensively.

This guide rail has obtained a patent.
Patent No. 2762055

Roller-Way

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Two circulating roller bearing and one V-gap rail are made up as one set. It is designed so that two sets are used together.
The V-gap rail has been ground to high precision to allow an extremely high level of straightness.
The use of rollers allows a large load carrying capacity in both the horizontal and vertical directions. In addition, as the circulating roller bearing is used, the surface of the stage is compact in size regardless of the strokes.
This mechanism is used for applications that require a heavy duty stage with high precision.

Ball-Way

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Two circulating roller bearing and one V-gap rail are made up as one set. It is designed so that two sets are used together.
Although the guide rail has been ground to high precision, precision may slightly vary depending on the precision of the surface to install the stage.
In the circulating ball bearing, since many steel balls are on contact with the R-gap of the guide rail, it provides a large load carrying capacity in both the horizontal and vertical directions.
As the circulating ball bearing is used, the surface of the stage is compact in size regardless of the strokes.
This mechanism is perfect for applications that require a heavy duty stage with high precision.

Ball-Bushing

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Two ball slide bearings and one shaft are made up as one set. It is designed so that two sets are used together.
Although the shaft has been ground, this mechanism has the normal precision since it is liable to change depending on the precision of the surface to install the stage or load.
This mechanism is for light load usage since the steel ball and the shaft are on point contact.
As the ball slide bearing is used, the surface of the stage is compact in size regardless of the strokes.
The main unit of the stage is lightweight as it is made of aluminum alloy. This mechanism is used for applications that require a stage with normal precision and light load.

Rotary Bearing

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This mechanism is designed so that the rotary bearings such as the angular bearing and the cross-roller bearing are used for guidance.
It has high precision and provides rattle-free rotation since the high precision pre-load angular bearing and the cross-roller bearing are used.
In addition, it provides a large load carrying capacity in both the horizontal and vertical directions, as the roller is used for the cross-roller bearing.
This mechanism is used for applications that require a heavy duty rotary stage with high precision.

An Overview of the Complex Coupling Mechanism

Instead of the traditional worm gear, we have adopted a feed screw mechanism for out complex coupling mechanism that is used to drive tilt stages.
By coupling this feed screw and the tilting part to a device that switches over between translatory and angular movement, this mechanism is able to pass on the straight line trajectory of the feed screw to a circular trajectory of the tilting part.
This mechanism takes advantage of the preciseness of using screws, resulting in high resolution, smooth motion, and superior durability.

An Overview of the Complex Coupling Mechanism

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Issues with Conventional Technology

■ Worm Gear Method
This is a general drive mechanism that uses a worm gear and worm-wheel. In this arrangement, part of the tilt stage upper table is made into part of a worm-wheel which is then driven by a worm gear. This mechanism has a fixed amount of backlash and if sufficient lapping adjustment is not performed, during operation, the worm gear can become heavy or uneven rotational torque can come about due to eccentricity.
In addition, the small area of contact between the worm gear and wheel can lead to problems with abrasion resistance.

■ Actuator + Spring Method
This is a mechanism used for general microscope stages that works by using an actuator and spring.
This backlash-free mechanism uses an actuator that pushes on the upper table and a spring that tries to return it back in the direction of the actuator.
There are several identified problems when using this mechanism. For example, the load on the actuator becomes quite high if a very powerful spring is used, the table can become unresponsive if it experiences a high load when being driven, or the table may not return to its original position if the spring force is to weak.

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Features of the Complex Coupling Mechanism

The complex coupling mechanism is driven by a feed screw and a specially designed coupling part. When compared with conventional technology, this design has the following features:

• Higher resolution when compared with the worm gear method.
• A specially designed coupling part allows free movement which absorbs any rotation irregularities.
• The small drive torque enables smooth movement.
• Durability is improved due to having a larger contact surface area than worm gears.
• Reliable movement control is possible due to the spring-free design.
• By changing the feed screw lead, the resolution and movement speed can be varied.

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Positioning Errors

When the straight line motion is converted into angular motion, there are angular positioning errors along the tangent curve between the amount of feed screw movement and the tilting part that actually moves, as well as along the sine curve of the distance between the feed screw and the tilting part. However in reality, microscopic positioning errors are within ±3° of the amount of movement which is much less that the ±5° you get with worm gear positioning. It is also possible to achieve high positioning precision by performing error compensation.

The above values were given from the following formula.
　　• The positioning error of the distance between the feed screw and tilting part (n = The feed screw displacement amount.)
　　　　　Positioning error = sin-(1 1mm/100mm)×n－sin-(1 n/100mm)
　　• The positioning error between the displacement amount and the actual moving tilting part (n = The feed screw displacement amount)
　　　　　Positioning error = tan-(1 1mm/100mm)×n－tan-(1 n/100mm)

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Patents

The “Complex Coupling Mechanism” has been registered under patent number 3848304 as a “Table position adjuster”.

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The Tilt Stage V-B Method Guide Rail

The tilt stage moves in an arc rather than in linear direction as with the X, X•Y, Z, and V stages. Therefore, if a guide rail with the same groove used for linear motion is adopted, there may be displacement between the V-gap and the steel balls which can lead to added stress.
In addition to reducing durability, the retainer (the assembly consisting of steel balls and the plates that they are held between) may also become misaligned causing loss of function.
In order to prevent this, we have developed a new type of guide rail based upon an entirely different concept.
For this guide rail, which is used in all tilt stage models of MM stages, we have redesigned the distance between the inner and outer arcs for the four points of contact with the steel balls. This helps maintain durability and greatly reduces retainer misalignment.

This guide rail design has been patented.
Patent number 2762055.

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