How Many Displacement Sensors Does One Injection Molding Machine Need? A Complete Plan for Injection, Clamping and Ejection
The injection molding machine is one of the most typical applications of magnetostrictive displacement sensors. Many customers ask: "How many displacement sensors does one injection molding machine actually need?" The answer is: a standard machine usually needs 3 (injection 1 + clamping 1 + ejection 1); fully closed-loop and multi-station machines need more. This article breaks it down by station so that it is clear in one pass where each sensor is fitted and which model to choose.
Station 1: injection position (screw displacement)
The stroke position of the injection cylinder / screw directly determines shot size and product quality. This station needs high-response, high-accuracy displacement feedback. The common choices are the Series 17 hydraulic-cylinder integrated (six outputs including 0-10 V, 4-20 mA and Start-Stop) or Series 12 (resolution 0.0015%, update as fast as 0.2 ms). The injection-position sensor is the core of closed-loop control; its accuracy directly affects shot-weight repeatability.
Station 2: clamping position (clamp stroke)
The clamping mechanism (toggle or direct-pressure) needs to detect clamp stroke and lock position, to prevent incomplete closing or over-travel. The clamping-position sensor is usually fitted in the clamp cylinder; choose Series 17 or the Series 16 flat electronics housing (saves radial space, suited to U-clevis hydraulic cylinders). Combined with clamp-force control, this gives an accurate closed loop on platen position.
Station 3: ejection position (ejector-rod stroke)
The ejector mechanism pushes the part out of the mould and needs to detect ejector-rod stroke, to avoid under-ejection or damaging the part. The ejection-position sensor likewise uses Series 17 (the all-digital electronic scale for injection molding machines: injection / clamping / ejection). The range is short and mounting space is small, so a compact type is more suitable.
Need more? It depends on the machine type and the degree of automation
| Machine type | Position-detection points | Quantity |
|---|---|---|
| Standard hydraulic injection molding machine | Injection + clamping + ejection | About 3 |
| Servo / fully closed-loop injection molding machine | Injection + clamping + ejection + wall-thickness / clamp-force auxiliaries | 4–6 |
| Two-platen / all-electric retrofit | Feedback on each motion unit separately | Add by station |
| Injection-molding peripheral robot | Positioning of each robot axis | 1 per axis |
All-electric injection molding retrofits, multi-component injection molding, high-speed precision injection molding and similar applications demand more channels and higher accuracy of displacement feedback. Contact us for a complete scheme by machine type.
