Selecting a conveyor pallet stopper by the pallet’s mass alone leaves common failures unresolved: the carrier overshoots, catches during release, or wears out prematurely. The specification must combine the load and approach speed, contact face, impact pattern, required stop position, downstream handshake, and recovery from faults. This guide helps production engineering, maintenance, and purchasing teams in Thailand compare pneumatic and electric options and prepare an RFP and FAT/SAT. A small workpiece pallet circulating through an assembly line is fundamentally different from a heavy shipping pallet handled by a forklift. A rating for one must never be copied to the other.
Define which pallet is being stopped and why
“Pallet” can mean a fixture carrier that moves a workpiece between stations, or a logistics pallet holding cases. Bosch Rexroth describes the electrical stop gates of its TS 2plus as components for separating its workpiece pallets. The page’s “up to 240 kg” is a figure for the system’s workpiece pallet mass under its own conditions; it is not a universal stopper rating or a permit to stop any shipping pallet. State the load unit precisely on the drawing and in the purchase specification.
A stop can serve several distinct jobs. It may hold a carrier until the next station is ready, establish an approximate stop point before a separate locating mechanism clamps the fixture, hold a carrier for an inspection dwell, or sequence arrivals at a merge. The stopper alone does not establish process datum accuracy, secure the workpiece, or maintain production sequence. Where a robot or inspection tool needs tight repeatability, assess a locating pin, clamp, or lift-and-locate mechanism separately. Show which component takes impact and which establishes the datum.
Retrofits often begin with an empty spot in the frame where a cylinder appears to fit. The design changes once the team checks whether a sensor can be placed upstream, whether the stroke clears the pallet underside, whether powered rollers will keep rubbing a held pallet, and whether maintenance can reach the mounting bolts. Read the conveyor system design guide and the merge, divert and accumulation guide to define the stop’s role in the complete flow.
Fix the operating envelope before comparing mechanisms
Start with a load and cycle data sheet, not a vendor comparison. Record minimum and maximum gross mass, actual speed immediately before impact, carrier length in the direction of travel, contact height and geometry, underside features, centre of gravity, stops per hour, and the number of carriers that may queue behind it. Include empty carriers, full carriers, startup, manual recovery, and abnormal transfer conditions. A queue that pushes continuously against the stopped carrier may impose a different duty from one isolated impact.
The SMC RSQ operating manual selects a cylinder by plotting transferred mass against conveyor speed for that particular series. Its worked examples belong to that selection chart; they are not approval for another model or manufacturer. The Festo DFSP document likewise distinguishes tip styles, actuation modes, and sensor mounting. Thus the pneumatic-versus-electric choice cannot settle capacity. Plot your measured operating point on the current chart for each candidate, check impact and duty restrictions, and ask the manufacturer or integrator to confirm application conditions in writing when the margin is unclear.
Record the following in the RFQ. If a value is missing, mark it “not measured” and schedule an on-site measurement before purchase.
| Item | Record | Consequence of omission |
|---|---|---|
| Load | Empty, typical and maximum gross mass; fixture and workpiece | Maximum case may fail to stop |
| Approach | Actual speed, acceleration, continuing drive thrust | Impact and sustained load understated |
| Contact | Face material, height, width and lateral offset | Uneven lever loading or pallet damage |
| Pitch | Minimum gap, queue length and cycle frequency | Repeated impacts or double release |
| Environment | Dust, oil, water, temperature, cleaning and air quality | False sensing, sticking or corrosion |
| Controls | Upstream and downstream Ready, reset and emergency-stop scope | Release into an unavailable station |
| Maintenance | Access, spare parts and local replenishment time | Small failure becomes long downtime |
Assess impact energy and contact, not mass alone
A first physical comparison is the translational kinetic energy E = 1/2 × m × v², where mass is in kilograms and speed is in metres per second. This equation is a screening aid, not a certificate of the stop’s absorbable energy. Doubling speed at the same mass quadruples this simple energy estimate. The real installation adds drive force, friction, elastic rebound, incline, off-centre contact and pressure from queued carriers. Therefore verify the actual operating point against the manufacturer’s mass-speed chart, allowable impacts, frequency and life assumptions.
Measure speed at the stop, rather than reading only the drive setting from an HMI. Include fixture, adapter and workpiece in gross mass, and test both empty and loaded carriers; an empty carrier may be less stable. A stop installed askew relative to travel does not receive the loading described by a straight-on catalogue illustration. Observe side-guide alignment, warped carriers and worn contact plates. Treat each deviation as a condition for the manufacturer selection check.
Even a shock-absorbing lever can see an unintended load path if the next pallet strikes the first while the lever is upright. SMC’s electric stopper manual specifically warns against that situation. If accumulation is required, compare an independently stopped upstream zone, wider spacing, or a second stop. Reproduce the shortest permitted gap and near-simultaneous arrivals in FAT rather than assuming the first carrier protects the stop.
Contact face and mounting stiffness determine durability
Matching mounting holes is insufficient when the carrier strikes above, below or to one side of the intended face. Overlay contact height, lever direction and lateral carrier variation on the mechanical drawing. Check whether feet or ribs underneath can ride over the tip or catch on it. Include at least one worn real carrier among test samples; nominal drawings often miss the contact created by ordinary wear.
A flexible bracket shifts stop position, sensor distance and lever return. Design the bracket and fasteners for repeated impact, not static weight alone. Follow the selected manufacturer’s mounting direction and tightening instructions, allow debris to clear the contact area, and provide a route for inspection and replacement. A thin convenient plate can make the stopper look compact while transferring the real cost into repeated downtime.
Compare pneumatic, electric and fixed stops
Pneumatic devices are candidates when suitable plant air is available and the job is a repeated up/down action. Check pressure at peak demand, flow, hose length, valve, speed controls, exhaust, and position after air or power loss as a system. Festo’s DFSP catalogue shows single-acting and double-acting versions and different tips. Do not infer that every model rises, retracts or remains in place on loss of air from the family name.
Electric devices are worth comparing where air piping is difficult or state monitoring through a controller is useful. Festo presents electric stoppers as material-flow products; Bosch Rexroth presents TS 2plus electric gates for workpiece separation in sections without air supply. Electric operation does not imply unlimited impact resistance. The SMC LEBQ manual warns that lateral conveyor load must not act during rod retraction and specifies conditions for homing and controller pairing. The mechanism and control sequence must remove or control that load before retraction.
A fixed or manual stop may serve low-frequency handling, adjustment positions, or maintenance blocking, but it does not automatically release individual carriers during production. Compare installed cost including sensors, electrical work, air supply, controls, guarding and spares, rather than actuator list prices alone.
| Comparison | Pneumatic | Electric | Fixed/manual |
|---|---|---|---|
| Supply | Plant air and control power | Electrical power and controller | Usually none |
| Control | Valve and position feedback | Drive/controller and status | Operator or fixed setting |
| Accuracy | Depends on contact, bracket and locating | Same; electric actuation alone is not a datum | Depends on adjustment |
| Key failure case | Air pressure loss and exhaust | Power loss, homing and lateral load | Runaway and manual handling |
| Capacity | Check exact model chart | Check exact model chart | Assess installed hazards |
Sense more than “pallet present”
At minimum, distinguish stop engaged or retracted, carrier arrival, and downstream availability. A presence sensor cannot prove that the stopper actually extended. Position feedback cannot prove that a carrier is seated at the contact face. Put the detection points on a drawing and show the missing or contradictory signal in a PLC alarm. Validate photoelectric detection with actual surface colours, reflective or transparent parts, dust and oil.
If the stopper is commanded to rise only after an arrival sensor detects the carrier, the worst timing can put its tip into the middle of the moving underside. Confirm engagement before enabling approach. Before release, require downstream Ready and check the candidate product’s restrictions on drive pressure acting during retraction. On contradictory sensors, stop safely and present the cause rather than looping automatic retries.
Write the downstream handshake as a state machine
“Release when downstream is clear” is too vague. Specify the states: awaiting arrival; stop engagement confirmed; carrier seated; downstream permission; stop retracted; carrier exited; stop engaged again. Define the confirming input, timeout, alarm and recovery action for each state. Consider a stuck presence signal, two carriers arriving together, and downstream Ready dropping immediately after release.
For signals crossing PLC boundaries, record what ON means, whether it is held or pulsed, how it resets, and how communication loss is treated. Define the scope of machine stop, fault and emergency-stop propagation. After maintenance removes a jam by hand, which PLC re-evaluates carrier presence and which operator action resumes automatic mode? If software assumes there is always one carrier, a manual intervention can leave its internal state wrong. Include counter reset permissions and an action log.
Control the following carrier and accumulation pressure
Whether a second carrier may touch the first affects both workpiece quality and stopper loading. If that contact is disallowed, provide a separately controlled upstream zone or a second stopper. Two stops are not automatically safe: spacing and the sequence that releases the upstream carrier toward the downstream stop still matter. Measure minimum pitch, stopping distance, sensor delay and restart acceleration.
In continuously driven rollers, a stopped pallet can keep sliding against the rotating rollers. Examine noise, abrasion, heat, motor load and creeping. Zoned drive such as MDR can remove some waiting pressure, at the cost of more zones, sensing and controls. The broader conveyor system design guide explains that choice; this article focuses on the actual stop point within it.
Assess safety as a line function
A stopper creates pinch points between carrier and frame, at a rising lever and during jam clearing. Determine access, guarding, emergency stopping, isolation and restart through a risk assessment of the complete line. Include residual air pressure, actuator holding condition and runaway on gravity sections. Do not omit a maintenance task because it is outside normal automatic operation.
After power or air returns, a carrier must not begin moving unexpectedly. The direction a product returns to on loss of supply and the safe state of the full line are separate questions. Prevent restart if the carrier crossed its stop or downstream Ready is unknown, and limit jog speed and range. A qualified safety specialist should determine the required safety functions and performance under the applicable rules and risk assessment.
Specify conditions of a Thailand installation
Existing Thai factories can have different generations of PLC, limited cabinet space, fluctuating air pressure, multilingual maintenance teams and long imported-spare lead times. Measure minimum running pressure and peak drops at the point of use. Check power capacity and restoration sequence for electric devices. Confirm candidate-model material and protection ratings against dust, mist, washdown, humidity and temperature. A broad claim such as “waterproof” is not enough.
Align Japanese engineering drawings with Thai maintenance instructions. Supply alarms, I/O lists, spare-part numbers and replacement procedures that the local team can use. Confirm local stocking and support before ordering. Product availability and pricing can change; request current quotations. No general Thai-market price is supplied here because the carrier, frame retrofit and control scope change the installed price substantially.
Mechanical requirements for the RFP
Attach load photos, outer dimensions, underside and contact drawings, mass range, fastest approach, allowable stop-position tolerance, cycle rate, following-carrier pattern and available envelope. “100 kg maximum” by itself does not state speed, contact height or frequency. Ask each supplier to identify the exact model and revision, selection evidence, warranty assumptions, exclusions, wear parts and life-test conditions in the same response format.
The mechanical boundary includes bracket and reinforcement, guide, contact plate, cable or hose protection, and replacement access. Decide who drills or welds the existing frame and how long production can be stopped for installation. A nominally interchangeable model may have a different tip height and contact point; verify any substitution against drawings and test samples.
Controls and safety requirements for the RFP
Include I/O, power and air requirements, upstream/downstream signals, timeout values, alarms, manual operation and power recovery. Define each signal’s ON meaning and what happens if downstream Ready disappears during a release. Specify the final PLC backup, change record, HMI languages and maintenance diagnostic screen.
Share the hazard analysis between the owner and integrator. Walk through access to clear a carrier, manual reverse, and possible lever motion with residual pressure. Do not design on the assumption that a guard will be removed during routine trial operation. Specify that resetting an emergency stop does not itself restart automatic conveying.
Compare complete installed and operating cost
Compare actuator, bracket, sensors, valve or drive, added PLC I/O, HMI changes, air and power installation, guarding, FAT/SAT, training and spares as separate lines. State installation downtime and commissioning support. “Durability tested” is less useful than a quotation naming the tested carrier mass, speed, cycle count and pass/fail criteria.
A single-point stopper fault can stop a whole line. A bypass or manual transfer may reduce downtime, but its procedure must protect sequence, identification and traceability. Measure jams, workpiece damage, line stoppage and recovery time before and after installation instead of estimating ROI solely from headcount.
FAT: reproduce boundaries and faults with real carriers
Use empty, typical and fully loaded carriers at low, normal and fastest approach speeds. A single stop of one maximum-weight carrier is not a sufficient FAT. Include offset loads, a worn carrier, shortest-gap double arrival, a changing Ready signal, a failed sensor, air-pressure drop, power loss and emergency-stop recovery. Plan potentially damaging tests within the manufacturer’s specified range and under controlled conditions.
Record stop-position spread, impact noise, rebound, contact from the next carrier, engagement and retraction time, signal latency, wrong release and recovery duration. Agree pass/fail values from this line’s requirements before ordering. A universal tolerance or cycle count copied from this article would be misleading. Save test conditions, software version, instruments, video and results for later fault analysis.
SAT: verify actual utilities and the existing conveyor
Factory FAT cannot reproduce installed frame stiffness, actual air pressure and the full variation of production carriers. At SAT, test stop and release during normal and peak operation, handshake with adjacent machines, and the site safety boundary. Have the local team perform shift startup, planned downstream hold, power restoration and restart after clearing a jam. If recovery is possible only by remembering undocumented steps, revise HMI messages and standard work.
Hand over installed model identifiers, drawings, I/O, PLC backup, spares, inspection tasks and escalation contacts. During the first weeks, trend stop cycles, alarms, wear and bolt condition; adjust sensor position or timeouts if evidence requires it. Record settings and reasons. Acceptance without maintenance handover often leaves the same fault to reappear months later.
Do not reduce the measurement record to “stopped” or “failed to stop.” For each trial, log carrier ID, gross mass, load position, approach speed, contact point, final position, rebound, engagement and retraction times, and sensor transition times on one line. When an unusual sound occurs, note where and under which conditions, then establish whether it recurs. For a pneumatic unit, record supply pressure both while stopped and during continuous operation; for an electric unit, record power status and alarms. These observations help separate a worn component from a speed or control-sequence problem.
Change management after handover is also part of acceptance. Extending a timeout or moving a sensor a few millimetres can take the equipment outside the FAT conditions. Record the before-and-after values, reason, approver, and tests repeated in the equipment history. If the supplier changes a PLC remotely, agree on backup, software revision and explanation to the local team first. A sequence of undocumented small setting changes makes the next failure much harder to diagnose.
Failure modes to address before buying
First, a mass rating is accepted without measuring speed and contact angle. Second, upstream conveying begins before the engaged signal, letting the carrier hit the lever midway. Third, a second pallet presses the first while the lever retracts, imposing side load. Fourth, a worn contact plate shifts the height of impact. These are specification and test problems, not merely post-installation tuning.
Fifth, after someone removes a jam, the PLC still “remembers” a carrier that is physically absent. Sixth, an imported proprietary part is chosen for a single critical stop without checking its replacement lead time. Evaluate who can safely recover abnormal flow as well as whether the normal stop works.
Pre-purchase checklist
- Identify workpiece carrier or shipping pallet, and document dimensions, underside and contact face.
- Measure empty, typical and maximum loads, fastest approach, offset load and worn carrier.
- Plot the operating point against current model-specific manufacturer documents and exclusions.
- Assess following-carrier pressure, double arrivals and load during lever retraction.
- Check bracket stiffness, guides, sensors, inspection and replacement access.
- Define Ready, arrival, engagement, exit and timeout as state transitions.
- Test air loss, power loss, emergency stop and restart after a jam.
- Put FAT/SAT conditions, pass/fail limits, records and maintenance handover in the RFQ.
FAQ: conveyor pallet stopper selection
Can I select a stopper from maximum pallet weight?
No. Assess speed, contact, duty and sustained drive force as well as mass. SMC’s RSQ instructions, for example, use the mass-speed operating range for that series. Check the current documents of the exact candidate.
Is a pneumatic or electric stopper cheaper?
The actuator price cannot answer that. Pneumatics need suitable plant air and piping; electric units need power and controller. Both need sensing, control changes, installation and spares. Compare total installed and maintained cost at your site.
Does a stopper provide precision positioning?
Generally, distinguish approximate stopping from the process datum. Impact absorption and carrier wear can move the contact point. Where needed, add a locator, clamp or lift-and-locate stage, and state the measured tolerance in the RFP.
Can following pallets accumulate against the stopped one?
Only if the selected mechanism and workpiece can tolerate it. A following impact onto the first carrier while a shock-absorbing lever is upright may violate product instructions. Compare an independent upstream zone and test actual minimum pitch and pressure.
How many cycles must FAT include?
There is no universal number. Set a plan from the required duty, manufacturer life assumptions and production schedule. Include boundaries, double arrival, sensor fault, power recovery and local-team recovery, not just a cycle count.
Conclusion: connect the model chart to line-level stop and release logic
Good selection measures the carrier operating envelope, verifies it against the exact product chart, and designs mounting, sensors, downstream handshake and abnormal recovery together. “Maximum weight” loses meaning outside the speed and system conditions behind it. Agreeing worst cases and acceptance tests before ordering makes competing quotations comparable on how the line will run.
TOMAS TECH can help a Thailand plant measure an existing conveyor, define a workpiece pallet stop point, compare mechanisms and controls, and prepare supplier and FAT/SAT requirements. Even before choosing a model, send carrier photos and the process to be stopped through our contact page.
References
- SMC, RSQ Series Stopper Cylinder Operation Manual (RSQ*-OM0080Q): https://www.smcworld.com/upfiles/manual/en-jp/files/RSQ-OM0080Q.pdf
- SMC, LEBQ Electric Stopper Cylinder / Controller Type Operation Manual (DOC1080290): https://www.smcworld.com/upfiles/manual/en-jp/files/DOC1080290.pdf
- Festo, Electric stoppers product page: https://www.festo.com/us/en/c/products/actuators-and-drives/electromechanical-actuators/electric-stoppers-id_pim236
- Festo, DFSP Stopper Cylinders catalogue: https://ftp.festo.com/public/pneumatic/SOFTWARE_SERVICE/Documentation/2016/US/DFSP_ENUS.PDF
- Bosch Rexroth, TS 2plus Transfer System and electrical stop gates: https://www.boschrexroth.com/en/at//c/transfer-system-ts-2plus/
