How Minimum Stroke Affects Position Sensor Performance in Hydraulic Cylinders

Why Very Short Strokes Can Cause Incorrect Position Detection

In hydraulic injection molds, position sensing is just as important as the hydraulic cylinder itself.

Modern molds rely on position sensors to verify that sliders, core pulls, locking elements and moving plates have reached the correct position before the next production step begins. Reliable position feedback is essential for machine safety, repeatability and process stability.

However, one design aspect is often underestimated:

the cylinder stroke must be long enough to allow the sensors to distinguish between the fully retracted and fully extended positions.

A real engineering case handled by the Vega Technical Department illustrates why extremely short strokes can create unreliable position detection and why relocating a sensor is not always the correct solution.

The Customer’s Request

A customer was using a CM032EGHGM020 hydraulic cylinder installed inside an injection mold.

The actual operating stroke of the cylinder was only 2 mm.

Believing that the problem could be solved by changing the sensor position, the customer asked whether it would be possible to move one of the sensor holes approximately 18 mm deeper into the cylinder body.

At first glance, the request appeared simple.

Move the sensor.

Detect the position.

Continue production.

However, the engineering analysis showed that the problem was much more complex.

Position Detection Depends on Stroke Length

The Vega Technical Department immediately identified the critical issue.

The problem was not the location of the sensor.

The problem was the extremely short cylinder stroke.

According to the technical evaluation, with a stroke of only 2 mm, both position sensors would detect the piston at the same time, making it impossible to distinguish correctly between the retracted and extended positions.

This is a fundamental principle of position sensing.

Sensors require sufficient piston movement to generate two clearly separated switching points.

If the movement is too small, the detection zones overlap.

Why Two Millimetres Are Not Enough

Many mold designers focus only on the mechanical movement required by the application.

From a mechanical point of view, 2 mm may be enough to move a small locking element or release a core.

From the perspective of position sensing, however, the situation is completely different.

Every position sensor has a switching zone rather than an infinitely precise switching point.

If the piston moves only a very short distance, both sensors may remain inside their respective switching ranges simultaneously.

Instead of receiving one clear signal, the control system may receive two valid signals at the same time.

This creates uncertainty in the automation system and may lead to incorrect machine logic.

The Importance of Minimum Stroke

Rather than recommending a simple modification, the Vega Technical Department explained that the minimum practical stroke for correctly using two sensors is approximately 4–5 mm.

This recommendation is based on engineering experience.

It ensures that:

  • the extended position can be detected reliably;
  • the retracted position can be detected independently;
  • the switching zones remain separated;
  • false simultaneous detection is avoided.

This type of engineering guidance helps prevent operational problems before they occur.

Engineering Is About Understanding the Entire Application

Another interesting aspect of this case is that the Vega Technical Department did not immediately approve the requested modification.

Instead, the engineers asked the customer to provide the mold drawing showing where the additional hole would be located.

This demonstrates an important engineering principle.

A hydraulic cylinder cannot be analysed independently from the mold in which it operates.

Sensor positioning depends on:

  • available installation space;
  • piston movement;
  • mold geometry;
  • accessibility;
  • mechanical clearances.

Only by understanding the complete application can engineers determine whether a proposed modification is technically feasible.

Cylinder Selection Also Includes Stroke Selection

The V450CM product documentation shows that hydraulic cylinders are available with a range of standard strokes and that intermediate requirements may be achieved by selecting the next longer standard stroke together with a stroke reducer, while special strokes are also available upon request.

This highlights an important design concept.

Choosing the correct cylinder does not simply mean selecting the required bore diameter.

The stroke must also be compatible with the sensing system, installation space and operational requirements.

A mechanically correct stroke may not always provide sufficient travel for reliable position detection.

Reliable Automation Begins with Good Mechanical Design

Reliable position sensing is not achieved simply by adding more sensors.

It begins with proper mechanical design.

When engineers determine the cylinder stroke, they should consider not only the required mechanical movement but also the space needed for accurate position detection.

A few additional millimetres of stroke can significantly improve sensor reliability, reduce troubleshooting and prevent unnecessary modifications after the mold has been completed.

Correct Stroke Design Ensures Reliable Position Detection

In Part 1, we saw that reliable position detection depends not only on the quality of the sensors but also on the mechanical design of the hydraulic cylinder.

The engineering case handled by the Vega Technical Department demonstrated that the customer’s request was not simply a matter of relocating a sensor.

The real limitation was the 2 mm operating stroke, which was too short to guarantee reliable and independent position detection.

Why Both Sensors Would Detect the Piston Simultaneously

One of the most important conclusions reached by the Vega Technical Department was that relocating the sensor would not solve the problem.

With only 2 mm of stroke, the piston would remain within the sensing range of both position sensors at the same time.

As a result:

  • both sensors could generate an output signal simultaneously;
  • the control system would be unable to distinguish the fully retracted position from the fully extended position;
  • machine logic could become unreliable.

Rather than improving the application, relocating the sensor could therefore create even greater uncertainty in the automation system.

Why 4–5 mm Is Considered the Practical Minimum

Instead of approving the requested modification, the Vega Technical Department explained that approximately 4–5 mm of cylinder stroke should be considered the practical minimum when two independent position sensors are required.

This recommendation provides sufficient piston travel to:

  • create two clearly separated sensing positions;
  • avoid overlapping switching zones;
  • improve signal stability;
  • reduce false detection;
  • increase machine reliability.

Although the exact switching characteristics depend on the sensor technology being used, providing adequate mechanical travel greatly improves overall system performance.

Position Sensors Must Be Considered During Mold Design

This engineering case demonstrates that position sensing should never be treated as an afterthought.

Many mold designers first determine the mechanical movement and only afterwards attempt to position the sensors.

Professional engineering follows the opposite approach.

Mechanical movement, cylinder stroke and sensor locations should all be evaluated together during the design phase.

This prevents costly modifications after the mold has already been manufactured.

Why the Mold Drawing Was Essential

Another interesting aspect of this case is that the Vega Technical Department did not approve the requested machining operation immediately.

Instead, the engineers asked the customer to provide the mold drawing showing the intended position of the additional sensor hole.

This request illustrates an important engineering principle.

Even a small modification to the cylinder body may influence:

  • structural integrity;
  • available wall thickness;
  • hydraulic passages;
  • sensor installation;
  • accessibility for maintenance.

Only by reviewing the complete mold assembly could the engineers determine whether the proposed modification was technically acceptable.

Choosing the Correct Stroke Is Part of Cylinder Selection

The V450CM Technical Catalogue shows that hydraulic cylinders are available with several standard stroke lengths and that intermediate requirements can often be achieved by combining a standard stroke with a stroke reducer, while special stroke versions are also available when required.

This demonstrates that cylinder selection involves much more than choosing the correct bore diameter.

Engineers should evaluate:

  • required mechanical movement;
  • available installation space;
  • sensor positioning;
  • automation requirements;
  • maintenance accessibility.

A cylinder that performs perfectly from a hydraulic standpoint may still create automation problems if its stroke is too short for reliable position detection.

Reliable Automation Depends on Good Engineering

One of the strongest messages of this engineering case is that automation reliability begins with sound mechanical design.

Adding more sensors or relocating existing ones cannot compensate for an insufficient cylinder stroke.

The most reliable solution is to design the hydraulic cylinder, sensor arrangement and mold geometry as one integrated system.

By considering these factors together, engineers can:

  • improve process repeatability;
  • reduce false machine alarms;
  • simplify troubleshooting;
  • minimise maintenance;
  • increase production reliability.

Conclusion

This engineering case demonstrates that reliable position detection cannot be achieved simply by relocating a sensor.

The Vega Technical Department showed that the real limitation was the 2 mm operating stroke, which was insufficient to separate the sensing zones of two independent position sensors. The engineers therefore recommended a practical minimum stroke of approximately 4–5 mm and requested the mold drawing before approving any modification, ensuring that the complete mechanical design was evaluated before changes were made.

This case reinforces one of the most important principles of hydraulic cylinder design:

Reliable position sensing begins with correct mechanical design. Cylinder stroke, sensor location and mold geometry must always be engineered together to achieve accurate and repeatable position detection.

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