| Principles of Positioning |
These tutorials will show you how to use locating pins and guides. The first tutorial will describe the principles of positioning, and will be followed by examples of the application of locating pins and guides.
(1) Principles of positioning
- What is positioning?... Positioning means maintaining a positional relationship between two objects with a high degree of precision. Either object: Serves as a locating base... (Example: Locating jig)
The other object: The object to be positioned onto the locating base... (Example: Workpiece)
- Place two objects in a configuration where their positional relationship is set in an effective manner (refer to [Fig. 1]).
Example:
1) Keep two dowel pins for positioning as far apart from each other as possible
2) Set the dowel pins in symmetrical positions
- Position the workpiece using three-directional constraint. (Four-directional constraint makes it impossible to insert or eject the part.)
- Select a positioning method based on the operation to be carried out (manual, automatic, prototyping, mass production, etc.) and the features (precision level, appearance quality level, material, etc.) of the workpiece.
- Do not fail to take measures against deteriorations in positioning performance due to wear or deformation.
(2) A variety of positioning methods
(Positioning methods are classified as shown below (refer to [Fig. 2]).
| Positioning Type |
Description |
| [1] Method that adjusts the position of the workpiece to the fixed datum plane |
Positioning of a workpiece by pressing its face against the datum plane. |
| [2] Method of adjusting the positioning face (point) |
Allows for adjustments of orientations using adjustable locating pins. |
| [3] Method using locating pins |
Positioning of workpieces using cylindrical or conical locating pins. |
| [4] Method using a V-groove |
Positioning of cylindrical workpieces in the longitudinal direction along V-grooves. |
| [5] Centering |
Positioning of cylindrical workpieces to their centers. |
| [6] Indexing |
Positioning of workpieces at specified distances over a linear distance. |
Locating Pins
How to use locating pins
- Two pins are generally used to position a workpiece on a locating fixture.
- One of the pins is round, whereas the other is diamond shapedand oriented as seen in Fig.3. This configuration will allow easier insertion and compensate for small dimensional misalignment when it comes to the distance between the two mounting holes in both plates.
- The two pins are of differing heights. The longer pin preliminarily positions a workpiece, and the shorter one provides accurate positioning when the workpiece is inserted onto it (refer to [Fig. 3]).
- The end of each pin has a round or conical shape or is chamfered for the purpose of maintaining workability (e.g., ease of insertion) and quality (e.g., prevention of damage) (refer to [Fig. 4]).
- If insertions are performed frequently, select a locating pin with a considerably large inserting guide at the end (spherical shape at the end + conical shape).
- The taper lead angle is large, 60 degrees or less, for light workpieces and manual operation, but it is frequently between 10 and 30 degrees for large-size workpieces that are difficult to handle, or when an automatic machine is used.
- Set the length of the pin locating portion based on the precision of (parallelism between) two parts and operation frequency.This lecture describes the key points of positioning methods using pins.
- As both the locating pin and the positioning hole into which it is inserted wear out and deteriorate in precision, adopt a mounting method that allows these parts to be replaced (refer to [Fig. 6]).
| Examples
- Parts that are not parallel to each other: Reduce the length of the locating portion.
- When insertions are performed frequently: Increase the length of the locating portion.
- For automatic machines: Increase the length of the locating portion, and allow larger clearance so that the contact length of the fitting portion can be reduced (refer to [Fig. 6]).
|
Positioning Adjusting Screws
How to Use a Positioning Adjusting Screw
Workpieces are positioned by the face of a positioning adjusting screw. By turning the adjusting screw, the positioning point in the screw axis direction can be adjusted.
[Photo. 1] and [Fig. 8] show an example of the adoption of a positioning adjusting screw for adjusting the height of a workpiece setting table.
- After positioning, lock the adjusting screw with a nut in order to keep it tightened. This operation needs to be repeated because the adjusted point moves out of position when this nut is tightened. It is advisable to make fine adjustments with the nut temporarily tightened, and perform positioning so that the final adjustment will end with slight deformation of the screw.
- When the material of an adjusting screw is not stainless steel, its end is heat-treated to a hardness level of approximately 45 Hrc or higher in order to reduce deformation and wear.
- Adjusting screws are available in two types, fine pitch threads and coarse pitch threads, in order to ensure conformity with the degree of precision in positioning.
- It is advisable to insert a stop pin into the opposing face of the workpiece with which the end of the adjusting screw comes into contact, as this face should possess a high level of plane precision and be made of a hard material (refer to [Fig. 9]).
- Using two positioning adjusting screws ensures efficient adjustment of the parallel precision of long workpieces (refer to [Fig. 10]) Positioning adjusting screws. This lecture describes positioning adjusting screws.
Locating Pin and a Locating Bushing in a Pair
How to Use a Locating Pin and a Locating Bushing in a Pair
Locating pins and locating bushings are used in pairs for the following purposes:
- Locating pin and a Locating bushing in a pair
- This lecture introduces examples of locating pins and locating bushings used in pairs.
Explanation 1
Free flow type automatic machines use many carriers. To reduce their weight and maintain their precision for over long periods of time, insert locating bushings into aluminum substrates.
Explanation 2
[Fig. 11] shows an example of item <3>. With a twist cylinder, linear and rotary motion can be obtained using an air drive. In this example, a small-size substrate is transferred using a vacuum pad. The locating pin and the locating bushing reduce the backlash (play) of the shaft structure of the twist cylinder. When a long pin is inserted, the pin and the bushing will become difficult to separate if there is no air release groove present. Make a relief hole in the bushing or a groove in the pin.
Explanation 3
[Photo. 2] shows a game machine comprised of a transfer robot employing an X-Y axis direct-acting unit and a rotary mechanism. These two units are mounted on independent base plates so that unit modification following a design change can be completed in a short period of time. Each unit is fastened to the frame of the machine body with a locating pin and a locating bushing. 1. In order to reduce deterioration in positioning precision attributed to wear, and maintain stable precision over long periods of time by making locating bushings (or locating pins) replaceable. 2. In order to increase positioning precision of actuators (e.g., twist cylinders for pick and place), and reducing the sizes of pin and bushing pairs.
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