When to use a Hollow shaft or Thru-shaft Rotary Encoder

When specifying a rotary encoder, should you opt for a Hollow Bore or a Thru-bore housing?  Usually, either design can work equally well. However, in some situations there are important reasons to choose one over the other.

https://www.amazon.com/CALT-Precision-Elevator-Encoder-GHH100-Tractor/dp/B01GJ457SK?ie=UTF8&*Version*=1&*entries*=0

In the parlance of Encoder Products Company, a Thru-Bore (or Through-bore) housing has a bore opening that passes completely through the encoder body.  The encoder is more or less a donut.

With a Hollow Bore (or Blind-Hollow bore) housing the bore does not pass completely through the encoder, with the shaft end residing inside the housing.  The depth of the bore varies from model to model, with some units only having a cap or cover on one side of the housing.

A Thru-Bore housing offers the most flexibility for shaft attachment.   Provided a means of securing the anti-rotation tether is readily available, a Thru-Bore encoder can be affixed to any point on the shaft in question.  Of course it's a good practice to confirm that runout and endplay limits are within the published tolerances of the encoder.

Here are three factors that favor use of a Hollow Bore encoder:

1. Environmental seal.  If your application is in an area where dirt, dust and moisture are in abundance, then consider applying a Hollow Bore encoder.  A Thru-Bore encoder has two exposed shaft seals that offer potential paths of contaminant ingress.  By opting for a Hollow Bore solution, one seal is protected from contaminants and potential leakage.  If the encoder is exposed to washdown or direct water spray, we recommend a Hollow Bore housing if possible.

2. Starting Torque.  Again, because a sealed Thru-Bore encoder has two shaft seals, the friction created by the additional shaft-seal interface is usually greater than that of a Hollow Bore housing.  This can translate into greater starting torque for Thru-bore encoders vs. Hollow Bore.  For example, the EPC Model 260 with an IP64 seal has 2.50 oz-in for Thru-Bore vs. 2.0 oz-in for the Hollow Bore. 

https://www.amazon.com/Hollow-Incremental-Encoder-1024PPR-Voltage/dp/B01GDTHIQU?ie=UTF8&*Version*=1&*entries*=0

3. Safety.  A Hollow Bore encoder minimizes hazards presented by an exposed rotating shaft.  Be sure to consult your relevant regulatory authorities regarding safety requirements.

For most applications the items above may be relatively minor points to consider when specifying a rotary encoder. However, failure to properly address them could contribute to less than optimum encoder longevity and performance, especially when an application pushes encoder performance requirements toward the limits.

Topics: rotary encoder, Encoder Products Company

When You Would Need A Hollow Shaft Rotary Encoder

When specifying a rotary encoder, should you opt for a Hollow shaft or a Thru-bore housing?  Usually, either design can work equally well. However, in some situations there are important reasons to choose one over the other.

https://www.amazon.com/Hollow-Incremental-Encoder-1024PPR-Voltage/dp/B01GDTHIQU?ie=UTF8&*Version*=1&*entries*=0https://www.amazon.com/Hollow-Incremental-Encoder-1024PPR-Voltage/dp/B01GDTHIQU?ie=UTF8&*Version*=1&*entries*=0

In the parlance of Encoder Products Company, a Thru-Bore (or Through-bore) housing has a bore opening that passes completely through the encoder body.  The encoder is more or less a donut.

With a Hollow Bore (or Blind-Hollow bore) housing the bore does not pass completely through the encoder, with the shaft end residing inside the housing.  The depth of the bore varies from model to model, with some units only having a cap or cover on one side of the housing.

A Thru-Bore housing offers the most flexibility for shaft attachment.   Provided a means of securing the anti-rotation tether is readily available, a Thru-Bore encoder can be affixed to any point on the shaft in question.  Of course it's a good practice to confirm that runout and endplay limits are within the published tolerances of the encoder.

Here are three factors that favor use of a Hollow Bore encoder:

1. Environmental seal.  If your application is in an area where dirt, dust and moisture are in abundance, then consider applying a Hollow Bore encoder.  A Thru-Bore encoder has two exposed shaft seals that offer potential paths of contaminant ingress.  By opting for a Hollow Bore solution, one seal is protected from contaminants and potential leakage.  If the encoder is exposed to washdown or direct water spray, we recommend a Hollow Bore housing if possible.

2. Starting Torque.  Again, because a sealed Thru-Bore encoder has two shaft seals, the friction created by the additional shaft-seal interface is usually greater than that of a Hollow Bore housing.  This can translate into greater starting torque for Thru-bore encoders vs. Hollow Bore.  For example, the EPC Model 260 with an IP64 seal has 2.50 oz-in for Thru-Bore vs. 2.0 oz-in for the Hollow Bore. 

https://www.amazon.com/CALT-Precision-Elevator-Encoder-GHH100-Tractor/dp/B01GJ457SK?ie=UTF8&*Version*=1&*entries*=0

3. Safety.  A Hollow Bore encoder minimizes hazards presented by an exposed rotating shaft.  Be sure to consult your relevant regulatory authorities regarding safety requirements.

For most applications the items above may be relatively minor points to consider when specifying a rotary encoder. However, failure to properly address them could contribute to less than optimum encoder longevity and performance, especially when an application pushes encoder performance requirements toward the limits.

Topics: rotary encoder,Encoder Products Company

Choose couplings accordingly to applications

Though couplings are well known and commonly used components in many rotary motion applications, the sheer variety of couplings can make selection rather daunting. While coupling usage is straight forward, most of the design time is spent in selecting the correct coupling type for an application.

Whether you’re building a new machine, or considering making modifications on an existing machine, check out the applications below and see how some industry professionals have applied couplings into their own builds. Though you may need to make adjustments before implementing these into your own designs, you can ensure these applications have already been tested and therefore function reliably.

Oldham Coupling Application

The Oldham Coupler is named for Irish engineer John Oldham who invented the three disc coupler in 1821, to resolve a paddle placement problem in a paddle steamer design. In this particular example we have a coupling used to connect a motor shaft to the drive roller of a conveyor. The Oldham coupling is a good choice for this application since high accuracy and zero back lash are not requirements. At the same time Oldham couplings have good misalignment characteristics and can transmit high torque.Flexible Coupling Application

Flexible couplings are used to transmit torque from one shaft to another when the two shafts are slightly misaligned. In this example, the test fixture is using torque transducer as torque senor for measuring torque. In this example, the flexible couplings are used to connect the motor and torque sensor with the work piece. These two couplings need to minimize any misalignment error since the torque sensor needs to lay as flat as possible. They also need to protect the sensor from overloading. Major characteristic of the flex couplings are very low or zero backlash, good torsion rigidity as good lateral and angular misalignment capabilities making them very suitable for this application.Disc Coupling Application

By definition, a disc coupling is a high performance motion control (Servo) coupling designed to be the torque transmitting element (by connecting two shafts together) while accommodating for shaft misalignment. It is designed to be flexible, while remaining torsionally strong under high torque loads. In this example, the coupling is used as part of the slide table in the welding station. The coupling connects the servo motor to ball screws that move the work piece table to the required position or positions. The disc coupling used here was recommended to be used with servo motors due to its low backlash, high torsion rigidity, and good allowable misalignment and torque capabilities.Couplings are standard machine components that require correct selection based on application requirements and user preference, installation and regular inspection.

During operation, the user should watch for external signs such as abnormal noise and vibration that indicate premature coupling failure. This helps with understanding what caused the failure and how and what to correct prior to installing a new coupling. During their life span, couplings should also be checked for signs of wear and fatigue.

For questions or assistance in selecting a coupling please contact me at amanda@china-encoder.com for assistance with our online configurator for coupling sizing and selection.