Stops are mechanical devices that arrest the motion of a moving member at a defined endpoint, either by direct contact, controlled deceleration, or energy absorption. The contact face — whether hardened steel, urethane, or a hydraulic dashpot piston — is the working component, taking the impact and converting kinetic energy into heat, deformation, or rebound. They exist to enforce a position limit when sensors, brakes, or servo control alone cannot guarantee it. On machines from Bosch Rexroth linear stages to Schuler stamping presses, a properly sized stop sets repeatability of position to within 0.02 mm.
Stops of Various Forms Interactive Calculator
Vary moving mass, speed, stop stroke, and cycle rate to see impact energy, average stopping force, heat load, and hard-stop severity.
Equation Used
The calculator uses the article kinetic energy equation for a moving member striking a stop. It also estimates average stopping force from work over the stop stroke, and heat load from repeated cycles.
- Moving mass is stopped from the entered velocity to zero.
- Average stopping force assumes constant deceleration over the entered stop stroke.
- Heat load assumes all kinetic energy is dissipated once per cycle.
- Hard-stop severity is referenced to the article guidance of roughly 4 J for hardened positive stops.
How the Stops of Various Forms Works
A stop works by interrupting motion when the moving member contacts a fixed reference. The simplest version is a positive stop — a hardened block bolted in the path of travel — which transfers the kinetic energy of the moving mass into the frame as an impact pulse. That pulse is what kills bearings, fasteners, and weld seams if you ignore it. So engineers reach for an adjustable end stop when position needs trimming, an elastomer stop or rubber bumper stop when the impact must be softened, and a dashpot decelerator when the energy is too high to dissipate as a single pulse.
The geometry matters more than people expect. If the contact face is not square to the direction of travel within roughly 0.5°, the moving member skids sideways on impact and the repeatable stop position drifts by 0.05 to 0.2 mm per cycle. If the stop is mounted on a cantilevered bracket that flexes 0.3 mm under load, you do not have a stop — you have a spring. We see this fail in the field constantly. The mounting must be at least 5× stiffer than the deflection budget you have allowed for the stopped position.
Failure modes are predictable. Hardened steel positive stops mushroom and chip if the impact energy exceeds roughly 4 J on a 12 mm diameter contact patch — you will see a bright crescent of cold-flowed metal forming after a few thousand cycles. Urethane bumpers take a compression set and shift the stopped position 0.1 to 0.4 mm after about a million cycles. Dashpots leak. If your travel limit suddenly grows by 2 mm overnight, check the dashpot oil seal before you blame the controller.
Key Components
- Contact Face: The hardened or elastomeric surface that takes the impact. For steel-on-steel positive stops, hardness should be 55-60 HRC and surface finish Ra 0.8 µm or better. Urethane shore-A 90-95 is the standard for soft stops on payloads under 50 kg moving at under 0.5 m/s.
- Adjustment Screw: On adjustable end stops, a fine-pitch threaded shaft (typically M12×1.0 or M16×1.5) sets the stop position. A jam nut locks it. The fine pitch matters — a coarse M12×1.75 shifts 0.04 mm per 8° of rotation, which is too sensitive for sub-0.05 mm repeatability.
- Mounting Body: The block or bracket that anchors the stop to the machine frame. Must be 5× stiffer than the allowed positional deflection. We typically machine these from 4140 pre-hard or weld them from 12 mm steel plate, never bolt them through sheet metal alone.
- Energy Absorber (dashpot or spring): Inside a hydraulic shock absorber stop, a metered orifice piston converts kinetic energy to heat in the oil. Stroke lengths run 10-100 mm, energy ratings 5-15,000 Nm per stroke. ACE Controls and Enidine are the named industry references here.
- Lock Nut or Set Screw: Holds the adjustment after setting. Vibration loosens unlocked adjusters within 50,000 cycles in our experience — always torque the jam nut to the spec, typically 30-60 Nm on M12.
Where the Stops of Various Forms Is Used
Stops show up everywhere a moving part needs a guaranteed endpoint. The reader searching for end-of-travel stops, hard stop blocks, or shock absorber stops is usually solving the same problem: a servo or pneumatic actuator overshoots, and a sensor alone cannot save the part or the operator. A properly chosen stop is the last line of defense, and on a high-cycle machine it is the difference between 10-million-cycle reliability and a quarterly rebuild. The right type — fixed, adjustable, elastomer, or dashpot — depends on the energy you need to absorb and how often you need to retune the position.
- Automotive Body Shops: Hardened positive stops on KUKA KR 210 robot weld-tip dressers, locking the dresser body at a known reference within 0.05 mm so the milling cutter trims the cap consistently.
- Packaging Machinery: Urethane bumpers on Bosch Rexroth pneumatic flow-wrappers absorbing the end-stroke of the cross-seal jaw 90 times a minute without telegraphing impact through the frame.
- Material Handling: ACE Controls MC600 series industrial shock absorbers stopping a 1,200 kg AGV pallet shuttle at the end of its track at Amazon FC distribution centres without rebound.
- Machine Tools: Adjustable carriage stops on Hardinge HLV-H toolroom lathes, set with a dial indicator so a turret hits the same shoulder ±0.01 mm over a production run.
- Elevator Industry: Oleo buffers — large hydraulic dashpot stops — at the bottom of elevator shafts in Otis and KONE installations, rated to absorb a fully-loaded car free-falling at 115% of rated speed.
- Aerospace Assembly: Drop-in pin stops on Mitsubishi MV-R series gantries used to set hard travel limits during composite ply layup, preventing a software-driven overrun from crashing the head into tooling.
The Formula Behind the Stops of Various Forms
The energy a stop must absorb is the practical sizing variable. At the low end of the typical range — say a 5 kg slide moving at 0.2 m/s — you are looking at 0.1 J, well within rubber-bumper territory. At the nominal mid-range, a 50 kg carriage at 0.5 m/s gives 6.25 J, which pushes you into urethane or small dashpots. At the high end, a 500 kg AGV at 1.5 m/s carries 562 J, and that is squarely industrial-shock-absorber territory. Get the energy calculation wrong by a factor of two and you either over-spend on an oversized dashpot or you destroy a urethane bumper in 10,000 cycles instead of 10,000,000.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Estop | Total energy the stop must absorb per impact | J (Joules) | ft·lbf |
| m | Mass of moving member at impact | kg | lb |
| v | Velocity at point of contact | m/s | ft/s |
| Fdrive | Driving force still acting during deceleration (pneumatic, gravity, motor torque) | N | lbf |
| s | Stop stroke or compression distance | m | ft |
Worked Example: Stops of Various Forms in a vertical lift gate stop on a brewery filler line
You are sizing the end-of-travel stop on the vertical lift gate of a Krones Modulfill HRS bottle filler at a craft brewery in Bend Oregon. The gate weighs 35 kg, drops at 0.6 m/s under gravity-assisted pneumatic action, and the cylinder applies an additional 180 N drive force during the final 25 mm of stroke. You need to choose between a urethane bumper, a small ACE MC150 dashpot, or a steel positive stop with a spring rebounder.
Given
- m = 35 kg
- vnom = 0.6 m/s
- Fdrive = 180 N
- s = 0.025 m
Solution
Step 1 — at nominal velocity 0.6 m/s, calculate kinetic energy:
Step 2 — add the work done by the pneumatic drive force during the stop stroke:
Step 3 — sum to get total nominal absorption requirement:
At 10.8 J the urethane bumper is borderline — shore-A 95 pucks rated for 8-12 J will compress to 80% of free height every cycle and take a permanent set within 200,000 cycles. That feels like the gate gradually closing 0.5 mm short of its target after a few weeks of production. The ACE MC150 dashpot is rated to 23 Nm per cycle, so it sits at roughly 47% of rated energy at nominal — its sweet spot for million-cycle life.
Step 4 — at the low end of the typical operating range, a slow jog at 0.2 m/s with no pneumatic assist:
That is a gentle bump — a steel positive stop would handle it forever. The dashpot, on the other hand, may not fully stroke at 0.7 J because the metering orifice needs a minimum velocity to develop damping pressure, so the gate could bounce.
Step 5 — at the high end, an emergency-stop scenario with cylinder full pressure and a 0.9 m/s impact velocity:
That is 81% of the MC150's rated capacity — still inside the envelope, but the urethane bumper would mushroom and crack on the third or fourth incident.
Result
The nominal energy the stop must absorb is 10. 8 J, which puts the ACE MC150 dashpot squarely in its design range. At the low-jog end of the operating range you are only seeing 0.7 J — so light the dashpot may not even stroke — while the high-end emergency case at 18.7 J still fits inside the dashpot envelope but would destroy a urethane bumper in three or four hits. If you measure rebound on the gate where there should be none, suspect (1) the dashpot orifice contaminated by line debris causing it to stiffen and act like a positive stop, (2) the mounting bracket flexing more than the allowed 0.1 mm, telegraphing a spring-back into the carriage, or (3) the dashpot piston seal leaking oil so the damping curve flattens and the residual kinetic energy pushes the gate back upward.
When to Use a Stops of Various Forms and When Not To
Picking the wrong stop type is the single most common mistake we see on retrofit work. The decision hinges on energy per cycle, allowable rebound, position repeatability, and how often the position needs to be tweaked during commissioning. Here is how the three main types compare on the dimensions that actually matter.
| Property | Hydraulic Dashpot Stop | Urethane Bumper Stop | Hardened Positive Stop |
|---|---|---|---|
| Energy capacity per cycle | 5 to 15,000 Nm | 0.1 to 12 J typical | Limited by frame stiffness, ~4 J on 12 mm contact |
| Position repeatability | ±0.1 mm (depends on stroke) | ±0.2 to 0.5 mm (compression varies) | ±0.01 to 0.02 mm |
| Rebound coefficient | Near zero (energy converts to heat) | 0.3 to 0.5 (significant bounce) | 0.6 to 0.9 (severe bounce) |
| Cycle life | 2 to 10 million cycles | 200,000 to 1 million cycles | 10+ million if energy is below threshold |
| Cost (industrial spec) | $80 to $600 per unit | $5 to $40 per unit | $10 to $50 plus mounting |
| Adjustability | Limited, fixed stroke | None — replace to change | Excellent with threaded body |
| Best application fit | High-energy, repeating end-of-travel impact | Low-energy soft stops, vibration cushions | Precise positional reference, low-energy |
Frequently Asked Questions About Stops of Various Forms
Almost always it is the carriage itself deflecting on impact, not the stop. A linear bearing carriage acts like a stiff spring — load it with a 50 kg payload and it will compress 0.05 to 0.3 mm before transferring force into the rail. The carriage rebounds, the encoder catches it at the rebound peak, and the controller reads an overshoot.
Check by mounting a dial indicator directly on the moving payload and comparing to the encoder reading at impact. If they disagree, you are seeing structural compliance. The fix is either a stiffer carriage assembly or commanding a controlled approach speed below 0.1 m/s in the last 5 mm.
Look at cycle count and rebound tolerance, not energy alone. If the machine cycles more than 500,000 times a year and rebound matters — for example, a part-positioning gate where bounce causes a misload — choose the dashpot every time. Urethane will compression-set and shift your position by 0.2-0.4 mm within months.
If the cycle count is low and rebound does not matter — say a swinging guard door that hits its end stop a few hundred times a day — urethane is half the cost and easier to source. Rule of thumb: above 200,000 cycles per year, dashpot. Below that, urethane is fine.
Dashpot damping is viscosity-dependent. The standard ISO VG 10 to VG 32 oils inside an ACE or Enidine unit can double in viscosity between 20 °C and 0 °C. On a cold start the orifice flow restricts harder, the piston moves slower, and the carriage feels like it is hitting a softer-than-spec stop because it decelerates over a longer fraction of the stroke.
If your facility runs below 10 °C overnight, specify the low-temperature variant — most manufacturers offer one with synthetic oil good to -30 °C. Or warm-cycle the machine for 5 minutes before production starts.
Yes, and we often recommend it on wide carriages where a single centred dashpot would induce yaw on impact. Two units sized at 60% of the total energy each (giving a 20% headroom) and mounted symmetrically about the carriage centerline keep the impact pure linear with no rotational kick.
The catch — the two units must be matched within 5% on damping curve, and they must contact the carriage face simultaneously within about 0.1 mm. Mismatched timing means one unit takes most of the load and fails early. Use shimmed mounting blocks to dial in the contact synchronisation.
Three causes account for almost every drift case we have diagnosed. First, the threaded interface itself — if the adjuster is M12×1.75 (coarse) instead of fine-pitch M12×1.0, vibration walks it loose between settings even with a jam nut. Switch to fine-pitch threads.
Second, the mounting block is bolted through a slotted hole and the bolt is not torqued enough to develop friction lock — the block creeps in the slot under repeated impact. Third, the stop face is mushrooming. After enough cycles the contact face cold-flows by 0.05-0.2 mm and the carriage finds a new resting position. Inspect the face under a 10× loupe; you will see a bright halo if it is mushrooming.
The moment a person, a $50,000 part, or a downstream tool can be hit if the stop fails. ISO 13849 and the equivalent ANSI B11 frameworks treat hard stops as safety-rated when they back up a controlled motion that, if it fails, presents a hazard. In that case the stop must handle the worst-case kinetic energy — typically the full motor torque plus rapid traverse velocity, not the normal end-of-cycle approach speed.
That sizing case is often 4 to 8× the nominal energy, which is why safety stops on machine tools are usually bolted directly to the casting and use steel-on-steel positive contact rather than dashpots. A dashpot can fail open if its seal blows; a steel block cannot.
References & Further Reading
- Wikipedia contributors. Shock absorber. Wikipedia
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