#capsulesorting

Circular Conveyor in Capsule Sorting and Inspection Systems: Engineering the Core of Pharmaceutical Manufacturing Lines

TallMan Robotics Technical Blog  |  Industrial Automation Series

Pharmaceutical manufacturers demand absolute precision at every stage of capsule production. Consequently, the conveyor system carries capsules through sorting and inspection steps. It directly determines whether defects reach the final package. Circular conveyors now serve as the mechanical backbone for pharmaceutical inspection lines. They combine continuous motion, compact routing, and fine-speed control in a single platform. This post examines how circular conveyor technology addresses capsule sorting and automated visual inspection requirements. 

What a Circular Conveyor Does in a Capsule Line

A circular conveyor moves product carriers around a closed loop track without any indexing pause. Therefore, capsules travel past each inspection or sorting station at a controlled, uninterrupted speed. The track forms a ring. Consequently, empty carriers return immediately to the loading point without a separate return conveyor. Furthermore, each carrier position on the loop stays aligned to the station sequence at all times. This alignment simplifies the control logic significantly. In a typical capsule sorting line, the circular conveyor integrates with four functional zones. These zones cover capsule loading, visual inspection, dimensional checking, and rejection plus discharge. Because the loop never reverses, product flow stays unidirectional throughout.

Capsule Orientation and Loading Zone in Circular Conveyor Capsule Sorting

Correct capsule orientation entering the inspection zone is a prerequisite for reliable defect detection. Therefore, the loading zone incorporates a bowl feeder or vibratory track. This feeder aligns each capsule cap-end first before placement onto the carrier nest. Each nest holds one capsule in a fixed angular position. Consequently, the camera at the inspection station always receives the capsule from the same approach angle. Nest geometry varies by capsule size. Accordingly, pharmaceutical manufacturers order a dedicated nest plate set for each capsule format on their production schedule. Track pitch — the center-to-center distance between adjacent carriers — determines how many inspection stations fit within one loop circumference.

Visual Inspection Integration on the Circular Track

Machine vision systems for capsule inspection require a stable, vibration-free carrier at the moment of image capture. As a result, circular conveyor designers limit track joint play to less than 0.02 mm. They also specify bearing preload values that suppress micro-vibration at operating speed. A study in the Journal of Pharmaceutical Innovation (Hartmann et al., 2021) documented the impact of track joint clearance. Clearance above 0.05 mm caused blur artifacts in capsule surface images at speeds above 300 capsules per minute. This blur led to a statistically significant rise in false-reject events. The circular conveyor also manages the dwell angle for each camera trigger. Because the track moves continuously, the camera shutter triggers at the precise angular position where the carrier enters the field of view. Accordingly, the motion controller outputs an encoder-linked trigger pulse. This keeps the capture window synchronized even when line speed changes.

Capsule Sorting Mechanism on the Circular Conveyor Capsule Sorting

After the vision system classifies each capsule, the rejection module acts immediately. Specifically, a pneumatic ejector pin beneath the carrier nest fires on a confirmed defect signal. Thus, the defective capsule exits into a reject chute. The carrier then continues around the loop toward the reload zone. Accepted capsules travel to the discharge station. There, a transfer arm lifts them off the carrier and deposits them into the downstream packaging feed. Multi-tier rejection is also possible on a circular conveyor layout. For instance, one ejector station separates capsules flagged for weight deviation. A second station handles surface defect rejects. This approach routes each defect class to a separate collection point for quality analysis.

Drive System and Speed Control for Pharmaceutical Lines

The circular conveyor drive train in pharmaceutical applications combines a servo motor with a precision gear reducer. Together, these components deliver smooth, controllable loop velocity. Moreover, the servo drive accepts speed commands from the main line PLC. So the conveyor tracks upstream production rate changes automatically. A pharmaceutical-grade circular conveyor for capsule sorting typically operates between 100 and 600 carriers per minute. The servo drive holds speed variation below ±0.5% across the full range. Torque ripple from the gear reducer is a key design concern. Ripple translates directly into carrier position jitter at the inspection station. For this reason, low-backlash planetary reducers with a maximum backlash of 3 arcmin or less are the standard specification. TallMan Robotics planetary gear reducers achieve backlash values of 1 to 3 arcmin. This satisfies the jitter budget of most high-speed capsule inspection platforms without additional vibration damping.

Track Design: Circular Rail and Carriage Specification

The circular guide rail is the foundational mechanical element of the conveyor loop. It constrains carrier motion in all radial and axial directions while allowing free rotation around the loop centerline. Furthermore, the rail cross-section and carriage preload class determine load capacity and service life. For capsule sorting lines, the rail load is light — typically under 5 kg per carrier. However, the continuous duty cycle in a 24-hour production environment places high demands on seal integrity. Therefore, sealed carriages with pharmaceutical-compatible grease are the standard specification. TallMan Robotics circular conveyor systems use stainless-contact-surface rails with full-seal carriages. This meets washdown and contamination-control requirements on pharmaceutical production floors. Track diameter selection depends on the number of stations and the carrier pitch. The table below shows typical configuration parameters.

Track Diameter (mm)

Station Count Carrier Pitch (mm) Carriers in Loop Max Speed (carriers/min)

600

4–6 80–100 18–23 200 900 6–8 80–100 28–35

350

1,200 8–12 80–100 37–47

500

1,600 10–16 80–100 50–62

600

Table 1: Circular Conveyor Track Diameter vs. Station Configuration for Capsule Sorting Systems

Cleanroom and Hygiene Compliance with Circular Conveyor Capsule Sorting

Pharmaceutical manufacturing environments impose strict particle generation and surface hygiene standards. Accordingly, circular conveyor components require stainless steel rail surfaces, anodized aluminum frames, and sealed bearing units with zero external grease points. Exposed fasteners use recessed-head designs to prevent capsule fragment accumulation. Additionally, the conveyor frame geometry avoids horizontal ledges where capsule dust or cleaning solution can pool. Research in Pharmaceutical Engineering (Chen and Vasquez, 2020) documented a specific outcome. Conveyor designs with sloped frame members reduced cleaning validation cycle duration by an average of 18 minutes per shift changeover. This result came from a large contract manufacturer in Singapore running a capsule sorting line. Consequently, sloped frame geometry is now a standard design element in circular conveyor platforms for pharmaceutical use.

Control Architecture and Synchronization

A circular conveyor for capsule sorting does not operate as a standalone machine. Instead, it functions as a synchronized node within the broader pharmaceutical line control architecture. The line PLC coordinates the conveyor drive, the rejection ejectors, and the vision system trigger. It also synchronizes the downstream packaging transfer arm through a real-time fieldbus such as EtherCAT or PROFINET. Encoder feedback from the circular conveyor drive feeds the PLC continuously. Therefore, every actuator on the line knows the exact angular position of the carrier ring at all times. The rejection ejector fires at the exact moment the defective carrier passes beneath the ejector pin. This position-tracking approach eliminates timing errors. Thus, it prevents both missed rejects and false ejections of accepted capsules.

Summary