Vacuum Grippers and Ejector Air Consumption

Vacuum Grippers andEjector Air Consumption

Hold the workpiece, reach vacuum on time, and account for every second of motive air.

1. Engineering answer: select for the handling duty, then calculate the air demand

A vacuum gripper should be assessed against the workpiece, contact arrangement, pressure difference, load direction, acceleration, leakage and complete handling cycle. Its ejector must remove air quickly enough to establish the required vacuum and continue to accommodate the leakage present during holding. Compressed-air consumption is a separate calculation based on the ejector's supported motive-air flow, actual operating time, re-evacuation events and release-air use. A maximum-vacuum figure alone answers none of these questions completely.

The central distinction is between holding force, suction flow and motive-air consumption. Pressure difference acting over effective contact area contributes holding force. Suction flow removes gas from the cup and connected vacuum circuit. Motive air powers an ejector and becomes demand on the compressed-air supply. These quantities must remain separate even when a catalogue prints their values in neighbouring columns.

A defensible selection therefore needs two linked records: a gripper-duty record describing the required handling result and an ejector comparison at the relevant supply, vacuum and exhaust conditions. A small average air demand can coexist with a difficult pickup transient. Conversely, a powerful ejector can consume air continuously while a poorly sealed cup never achieves the required grip.

Start by resolving the failed or required outcome. Is the problem insufficient holding, slow pickup, loss of vacuum during transfer, unreliable release, excessive consumption or inadequate response after an interruption? The answer determines which measurements and component data matter. Increasing compressor pressure or buying the ejector with the highest catalogue vacuum should not be the automatic first response.

2. Scope and boundaries with the surrounding engineering pages

It develops the gripper-duty and ejector-comparison asset required by the fixed content map.

This page does not reproduce the full vacuum-pump technology library or replace the original equipment manufacturer's selection process. Mechanical grippers, magnetic handling, Bernoulli devices and high-flow area grippers can have different load mechanisms and operating requirements. An equation for a sealed suction cup cannot be transferred to another gripping principle simply because both products appear in a vacuum catalogue.

The calculations below are explicitly bounded teaching models. They support requirement definition, source-data reconciliation and preliminary comparison. They do not assign a safe working load, establish a protective function or approve transport of an actual suspended load. Equipment-specific limits, applicable machine requirements and the responsible engineering review remain separate.

The document distinguishes supplied project foundations [S], supplementary manufacturer references [R], and original requirement methods, derivations and fictional examples [N]. The uploaded supplier-reference document is a resource index, not measured performance. The accompanying compressor-company graphic is not evidence of a vacuum-gripper rating, an ejector curve, a current market ranking or a Reddy supplier relationship. Neither is used to invent component performance.

3. Define the workpiece and handling sequence before selecting cups

Describe the object that must be handled, including its permitted variants. Record mass, dimensions, centre of gravity, stiffness, local surface geometry, porosity, coating, contamination, temperature and permissible contact marks. A smooth sample can differ materially from a production batch containing seams, labels, folds, damaged packaging or dimensional variation. The design brief should identify the conditions it actually covers rather than treating one successful pickup as universal evidence.

Define the path and orientation throughout the cycle. A top pickup followed by a sideways transfer and rotation does not remain one simple vertical load case. Include acceleration, braking, reversal, vibration and the load configuration when motion stops. Distinguish the normal production path from the separately assessed response to an interruption. Do not assume that the largest commanded acceleration is the only mechanical demand.

Specify the evidence source for each entry. A measured mass, supplier-defined cup area and approved robot trajectory are different from planning assumptions. Keep assumptions usable but visible. Where the workpiece family is too broad for one configuration, create separate recipes or reject the proposed grouping; a broad product name does not establish one common gripping duty.

4. Use vacuum pressure definitions that cannot reverse the decision

Store absolute pressure, gauge pressure and positive vacuum depression as different quantities. For a local atmospheric pressure p_atm and positive depression Δp, the cup absolute pressure is p_cup,abs = p_atm − Δp. A gauge display of −60 kPa means a 60 kPa depression relative to its atmospheric reference; it does not mean an absolute pressure of −60 kPa. The pressure difference available for a conventional suction cup is the external pressure minus the pressure inside its sealed region. [S1; N2]

A percentage vacuum needs its declared convention. When it means 100 × (p_atm − p_cup,abs)/p_atm, its pressure difference depends on the atmospheric reference. Do not convert every supplier percentage into one fixed absolute pressure without checking the convention. A declared 100 kPa atmosphere in a teaching example is not a measurement of the user's site.

Record the pressure at the cups or the boundary demonstrated to represent them. During evacuation and leakage flow, a sensor near the ejector can indicate a different pressure from a distant cup. A reading is meaningful only with its location, measurement reference, timing and operating state. A sensor on an isolated branch can retain a favourable value while another contact has already lost its seal.

Pressure sign matters in control descriptions. In absolute units, weaker vacuum means a larger number. An air-saving controller might stop generation at a lower absolute pressure and restart when pressure rises. In positive-depression units, the same event moves in the opposite numerical direction. Store thresholds with their quantity type and show both the condition and its meaning; avoid an unexplained “high vacuum alarm” label.

5. Establish normal, shear and moment capacity separately

For a sealed contact under a stated pressure difference, the theoretical normal-force contribution is F_N = Δp × A_eff. With Δp in pascals and effective area in square metres, the result is newtons. This is a pressure-force identity, not an equipment rating. Effective area should come from the cup's applicable definition or validated contact model; its outer diameter, bellows envelope and sealing footprint need not describe the same area. [S1; N2]

For a simple top lift with only vertical motion, a teaching demand is F_required = S × m × (g + a_up), where S is an explicitly selected design factor. The factor's basis belongs to the responsible application design. It should not be copied from an unrelated worked example or added a second time when the supplier's permissible load already incorporates the intended allowance. Manufacturer holding guidance distinguishes load cases and requires surface-specific consideration of friction. [R1]

For a vertical contact face supporting a downward load through friction, the simplified shear relationship F_shear ≤ μF_N can be useful. It requires a justified coefficient and an appropriate contact model. Oil, dust, moisture, surface coatings and deformation can change the actual behaviour. The worked values in this document are not universal coefficients. Simultaneous normal separation, shear and overturning require the applicable combined-load assessment; passing isolated scalar calculations is not proof of combined capacity.

Include moments from an offset centre of gravity, tool acceleration and uneven cup contact. The total of all theoretical cup forces can exceed total demand while one row is overloaded. Cup peel, compliant mounts, workpiece bending and loss of one seal can invalidate an equal-sharing assumption. Evaluate the actual support geometry and the manufacturer's applicable limits before accepting an arrangement.

6. Choose contact geometry and cup construction around the actual surface

Cup selection begins with the available contact region. Identify whether the cup can form a complete seal throughout workpiece variation and movement, not merely whether its nominal diameter fits the drawing. A label edge, embossed feature, groove or seam can cross the sealing lip. A curved panel may provide less effective contact than a flat teaching area. Soft packaging can deform as pressure falls and alter both the area and the volume being evacuated.

Flat, bellows, oval, foam and specialised contact arrangements should be compared using their documented functions. Compliance can accommodate height variation but also permit movement or add volume. A large area can reduce the pressure difference needed for a theoretical force while increasing contact footprint, bending sensitivity or evacuation demand. More cups can improve geometry, but also add leakage paths, connectors and opportunities for an uncovered branch.

Record material compatibility with the workpiece and environment. Temperature, oils, cleaning agents, abrasives, product-contact requirements and acceptable marking all affect the choice. Do not infer suitability from cup colour or a general “industrial” description. A material approved for one cleaning regime should not automatically be substituted after a maintenance stock change.

Treat preload and support as part of the application. The mechanism must establish contact without damaging the workpiece, and the mounts must accommodate the allowed variation without creating an uncontrolled load distribution. Define the permissible cup compression, approach behaviour and replacement attributes using manufacturer information. The gripper-duty record should retain which cup family, mounting and workpiece condition were used for any accepted trial.

7. Distinguish sealed handling from continuous-leakage duty

In an approximately sealed application, the generator's main task can be evacuation followed by occasional leakage replacement. In a porous application, gas can enter continuously through the workpiece, so sustained suction flow at the operating vacuum becomes central. Piab's vacuum-technology guidance makes this distinction between non-porous and porous handling. It also separates central and local vacuum arrangements. [R2]

Real production objects need evidence rather than labels. A metal component with a groove across the lip can leak; a coated cardboard surface may seal better than its material category suggests. Contact leakage, material permeability, uncovered cups, fittings and valve leakage should be distinguished where possible. Their response to pressure, workpiece compression and time may differ.

At a steady operating point, the generator must remove the gas entering the connected vacuum circuit. If suction and leakage flows are expressed at the same reference condition, their values can be compared directly. If one is an actual inlet-volume flow and the other is a reference-volume flow, first reconcile the bases. A numerical comparison of two values labelled L/min is not sufficient.

A shortfall near the required vacuum cannot be solved by borrowing the ejector's maximum suction flow at an open inlet. The relevant curve point is the one associated with the required vacuum and actual supply conditions. When leakage equals the available removal rate, pressure stops improving in the simplified balance. A larger nozzle, improved contact, different cup area or another generation technology may be considered, but each changes more than one part of the duty. Verify the complete combination rather than purchasing by a single maximum value.

8. Read ejector performance as a family of related curves

A useful ejector record contains the exact model, nozzle or cartridge configuration, supply pressure, exhaust condition, suction characteristic, motive-air consumption and vacuum limit. Preserve the units and reference states. SMC's selection guide distinguishes suction flow from air consumption and shows how leakage is interpreted against the selected ejector's flow characteristic. Its product-specific selection shortcuts are not universal calculation rules here. [R3]

Compare candidates at the same task: the same contact layout, target pressure, connected volume, leakage case, cycle timing and supply envelope. Keep supply pressure at the ejector distinct from the compressor-room value. An apparently efficient unit can be unsuitable when its required supply is unavailable during concurrent machine operation.

Single-stage and multistage ejectors should be assessed from their actual curves and functions, not ranked categorically. One configuration may prioritise high suction flow; another may reach a deeper vacuum. An integrated sensor, check function or release valve changes the functional boundary. Avoid adding a separate accessory or air allowance when the declared package already includes it, and do not assume those functions exist when they are optional.

9. Decide where vacuum is generated and which contacts share a circuit

A central generator can serve several contacts through a common distribution path. Local ejectors can reduce the length of the vacuum connection and permit more independent control. A hybrid arrangement can group contacts by workpiece zone. These are alternative architectures, not automatic rankings of energy use or reliability. Their behaviour depends on shared supplies, exhausts, valves, sensing and the actual contact arrangement. [R2; N1]

For a shared circuit, assess the effect of an uncovered or leaking cup on the remaining contacts. A common sensor may report the combined pressure without identifying the affected branch. Flow restrictors or automatic shut-off devices can limit some leakage paths, but their suitability depends on their operating principle and the workpiece. They can also affect evacuation and release. Do not assume they isolate every failure or create redundancy by themselves.

For local generation, record the additional compressed-air lines, valves, sensor channels, moving mass, electrical connections and maintenance access. A short suction tube is useful only if the local motive-air supply remains adequate. Several local ejectors starting together can create a supply transient that did not exist with a differently sequenced central source.

Define the isolation boundary for every retained vacuum region. Identify whether a check valve separates the source from the cups, whether a branch contains additional storage, and which volumes are vented during release. A diagram or component schedule should distinguish a shared source from genuinely separate holding zones. Independence requires analysis of common-cause paths, not simply a count of ejector cartridges.

10. Include cup, tube, filter and manifold volume in response assessment

The volume to evacuate includes all connected spaces whose pressure falls during the relevant event: cups, mounting passages, hoses, manifolds, filters, valves and any vacuum reservoir. Schmalz's evacuation guidance explicitly totals these contributions.

For a uniform circular tube, V_tube = πd_i²L/4. Use its internal diameter and consistent units. Add different segments separately so their length and bore remain available for restriction assessment. A catalogue outside diameter or thread size is not a substitute for the actual internal passage.

Volume and conductance are linked design questions. Increasing tube bore may improve flow at the same pressure difference but also increase the gas inventory. Shortening the line can reduce both effects, subject to mechanical routing, access and moving-mass constraints. A large reservoir may slow pressure loss after source isolation but increase initial evacuation duty. These consequences should be evaluated together instead of treating “more volume” as an unconditional improvement.

Distinguish geometric volume from recurring consumed air. The gas removed from the vacuum side is not itself the compressed air powering the ejector. A tube continuously held under vacuum is not evacuated from atmosphere every cycle unless its topology actually vents it. Likewise, repeatedly vented tooling should not receive an unrealistically favourable assumption that all vacuum remains between cycles.

The calculation must identify its initial pressure. After a brief interruption, residual vacuum can change the next pickup time. A model that always starts at atmospheric pressure may be conservative for one sequence and incorrect for another; record the actual intended state rather than hiding it in a nominal “cycle time.”

11. Use an evacuation model that matches the suction-flow definition

For a rigid volume V, ideal gas, approximately uniform constant temperature and negligible leakage, constant effective pumping speed S measured as actual volume per time at the vessel pressure gives dp/dt = −Sp/V. Integrating between positive absolute pressures p_initial and p_target yields:

t = (V/S) × ln(p_initial/p_target).

The time unit follows V/S. Use V in litres and S in litres per second for seconds. S must represent the effective speed at the evacuated boundary, including the assumed connecting path. Substituting a catalogue maximum reference-flow value into this expression changes the model's meaning. [N2; R4 for the general evacuation relationship]

When suction is instead reported as q_s,ref at reference pressure p_ref and reference temperature T_ref, an isothermal rigid-volume balance is:

dp/dt = (p_ref/V) × (T/T_ref) × (q_leak,ref − q_s,ref).

The equation assumes the same gas and an ideal-gas treatment. With equal temperatures and constant net reference removal, evacuation time is V × (p_initial − p_target) / [p_ref × (q_s,ref − q_leak,ref)]. This linear pressure-change model and the constant-actual-speed logarithmic model are different assumptions; neither is a universal substitute for a measured pressure-dependent characteristic.

For a pressure-dependent q_s,ref(p), integrate across the supported range or use a documented numerical approximation. The net removal must remain positive toward the target. If leakage equals or exceeds removal over a required interval, return an unresolved or unreachable target under that model—not a negative time. Preserve curve interpolation, temperature, dead volume and leakage assumptions.

A real pickup also includes valve delay, contact establishment, cup deformation, pressure nonuniformity, sensor response and confirmation logic. The calculated evacuation interval is only one part.

12. Interpret pressure-rise testing and reserve time within their assumptions

A controlled, safely supported pressure-rise observation can help quantify gas ingress into a defined isolated vacuum volume. Under constant volume, equal gas/reference temperature and ideal-gas assumptions, reference leakage is:

q_leak,ref = (V/p_ref) × (p_final − p_initial)/Δt.

Use absolute pressures and a common pressure unit. During leakage into a vacuum region the absolute pressure normally rises. The relationship identifies an equivalent total gas-inflow rate for the stated interval; it does not locate a leak or prove that the rate remains constant at another pressure. Thermal drift, cup deformation, valve leakage and gas release from materials can also affect the pressure trace. [N2]

Where an approximately constant ingress rate is defensible, the modelled time for pressure to rise from p_start to p_limit is V × (p_limit − p_start)/(p_ref × q_leak,ref). The model must identify whether p_limit is a control restart threshold, a process hold threshold or another requirement. Those limits are not interchangeable.

A zero pressure rise within instrument resolution does not establish zero leakage or unlimited retention. Report the observation and its resolution. An observed zero, a missing measurement and an unresolvable change are different records. Never return infinite safe holding time from a rounded zero-leak value.

Reserve time is only a screening result until the worst relevant workpiece, configuration and operating conditions have been assessed. A reservoir and check valve do not protect against every cup detachment or workpiece rupture. Fault trials require the approved machine procedure and safe support. This page does not instruct users to interrupt a live vacuum supply while a load is suspended.

13. Define gripping confirmation and air-saving control independently

Separate the signals that command vacuum, indicate usable measurements, confirm a process threshold, permit movement and request release. A commanded ejector can fail to establish vacuum; a pressure switch can change state without proving that every contact is engaged. Conversely, a good pressure value may remain after the workpiece is placed down. The circuit foundation already separates observations, permissions, reset and physical state.

An air-saving function commonly interrupts motive air after an accepted vacuum condition and restarts it as leakage weakens the vacuum. Piab's P3010 documentation describes incoming-air control and adjustable switching behaviour. This establishes the function, not a universal threshold or saving. [R5]

Define the stop-generation threshold, restart threshold, movement-permission threshold and low-vacuum response separately. In absolute-pressure notation, stop-generation pressure is normally lower than restart pressure. The acceptable relationship to a movement-permission limit must include sensor uncertainty, hysteresis, delay and pressure change during the response interval. A numerical difference between two switch values is not automatically an adequate operating margin.

Avoid using a long debounce time to hide an unacceptable pressure dip. Filtering can suppress noise but also delay recognition of a genuine condition. Record the sensor's location, sampling/update rate, filtering, signal-age rule and the meaning of each status. Data validity and pressure adequacy should remain separate in the interface.

Record what happens if air saving cannot stabilise the process: excessive restart frequency, failure to recover, an uncovered cup or loss of a required signal. Whether continuous suction is allowed as an operational fallback must be explicitly decided. It cannot silently replace an unresolved holding or safety requirement, and it changes the consumption case.

14. Calculate motive-air consumption from the complete event ledger

For motive-air flow q_m,ref in reference litres per minute and event duration t in seconds, supplied volume is V_m,ref = q_m,ref × t/60. Sum the non-overlapping intervals for each physical supply path. The cycle record should distinguish initial evacuation, continuous or pulsed holding, re-evacuation, release blow-off, standby and any separately documented pilot consumption. [N2]

The same units do not justify adding vacuum-side suction volume to motive-air volume. The former is gas removed from the vacuum circuit; the latter is compressed air drawn from the plant. Ejector exhaust contains both streams on a mass basis, but it is not appropriate to add their unconverted actual volumes at different pressures or to bill suction flow as compressor demand.

Average reference flow follows total reference volume divided by the corresponding time. Per-cycle consumption needs an explicit cycle definition. Per-good-pick consumption should include failed attempts and recovery air within the agreed boundary, divided by accepted completed picks. A lower air volume per attempt can be a worse result if successful output falls.

Annual air use needs actual operating hours, cycle count and product mix. A possible reduction in compressed-air volume is not automatically the same percentage reduction in station electricity. The electrical result depends on compressor control, demand profile and the system boundary. Retain air-volume savings separately until an appropriate energy measurement or documented project model supports a further calculation.

15. Verify the motive-air supply, exhaust and preparation together

Measure or establish pressure at the ejector inlet while the relevant generation and release events occur. A nearby no-flow gauge does not show losses across the regulator, supply valve, filter, hose and couplings at peak demand. Include concurrent users and the minimum permitted supply case. Product performance should be read at that condition, with its specified exhaust arrangement.

An ejector's exhaust path carries motive gas and entrained suction gas. Restrictions, remote exhaust routing or shared silencers can affect its operating condition. The relevant manufacturer data must govern permitted arrangements. Do not remove a silencer or modify an exhaust solely because a pickup becomes faster; noise, discharge location and component conditions remain part of the installation.

Specify air quality from the ejector and process requirements, not from a generic FRL assumption. Filtration protects appropriate pathways, regulation controls the supply envelope and lubrication is used only where the selected equipment requires it. Vacuum-side filters need their own pressure-drop, contamination and liquid-ingress assessment. A clean compressed-air supply does not prevent dust from entering through the workpiece side.

Record where maintenance can change performance: filter element type, hose bore, silencer, release-valve setting, regulator range, nozzle cartridge or firmware configuration. A replacement with matching threads can still change flow, volume, switching behaviour or air consumption. Keep the accepted assembly identity and retest the affected duty after a material change.

16. Treat release as a controlled process event, not an uncounted air pulse

A successful pickup is not a complete handling cycle. The workpiece must be released at the required location without sticking, bouncing, double picking or disturbing neighbouring parts. Establish when support is available, when release is permitted and how completion is detected. A vacuum-off command is not proof of physical separation. The supplied circuit material explicitly keeps release and retention separate.

Passive venting and positive blow-off behave differently. Passive venting admits gas into the vacuum region; blow-off supplies positive-pressure air through the selected path. The latter can shorten some releases but also add consumption and force. The correct amount depends on the actual cup, volume, workpiece and supported design. Do not turn a teaching pulse duration into a commissioning setpoint.

Identify whether blow-off passes through the same valve or has a separate supply. Check valve states, possible cross-flow into other cups and the behaviour of any vacuum-retention element. On a common manifold, a release at one branch may affect another branch still holding. The functional design must establish which connections are possible in each state rather than assuming a label such as “independent channel” resolves the issue.

Record release-air volume as part of the normal and fault cycles. If the supplier's complete-cycle consumption already includes it, do not add it again. If the release uses a separate positive-pressure source, preserve that source identity and reporting basis. Stop the event ledger at the actual defined completion point, not at the end of the vacuum-generation command.

17. Design source loss, grip loss and restart as different situations

Loss of compressed-air supply, electrical power loss, a broken suction line, a porous workpiece and an uncovered cup can produce different pressure histories. A retained-vacuum device may help in one event while providing little benefit in another. A normal process stop is not proof that a vacuum-held load remains supported for the necessary duration.

Manufacturer vacuum-selection guidance calls for assessment of workpiece-drop risks associated with loss of air or power. The competent machine and safety design must determine the necessary support, containment, monitoring and response. [R3]

Identify the behaviour of the exact valves when control power disappears but compressed air remains. A normally open and normally closed supply arrangement can behave differently. Likewise, a blow-off function must not activate merely because a communication value became invalid. Store the intended response separately from the actual manufacturer's uncommanded state so incompatibilities remain visible.

Restart should reconcile workpiece presence, support, actual vacuum state, valve commands, recipe and signal validity. Restoration of a pressure reading or network connection is not by itself permission to resume an interrupted robot movement. Reset and new production start remain separate actions under the applicable machine requirements.

Its purpose is to identify the missing design evidence before a real installation or trial, not to replace the responsible personnel or procedure.

18. Compare candidates using the same duty, not a weighted marketing score

Compare gripper and ejector combinations, not ejectors in isolation. A candidate can use less motive air per second but need longer evacuation or more re-evacuation, producing greater cycle consumption. Another can provide excellent maximum vacuum but insufficient flow at the actual leakage condition. Keep mechanical coverage, pneumatic response, functional behaviour and consumption as separate decisions.

Do not conceal a mandatory failure inside a high total score. One candidate can be promising on consumption and remain on hold for mechanical retention. Another can satisfy normal production while lacking evidence for a required variant. A useful comparison says exactly what is covered and what remains unresolved.

Where electric vacuum generation is a credible alternative, compare the complete duty and energy boundary. Include initial evacuation, leakage, standby, controls, pipework, maintenance and response. Do not compare an ejector's instantaneous motive-air volume with a pump's electrical nameplate as though they were directly equivalent costs.

19. Commission with workpieces, timestamps and pressure at the right point

The acceptance plan should identify the exact configuration, workpiece variants, allowed operating envelope, sequence and required evidence. Mechanical contact, pneumatic performance, production quality and protective functions need their own acceptance criteria. A checklist completed on paper is not a physical test result. Where representative parts vary, identify how the chosen test set covers that variation rather than reporting a single best case.

Record command time, first contact where observable, vacuum-generation start, cup-pressure trace, threshold confirmation, movement start, transfer completion, release command and physical release. Separate measurement uncertainty and sampling limitations from controller timestamps. A pressure trace at the ejector may support source diagnosis while leaving the cup boundary unresolved.

Measure motive-air use on the agreed supply boundary or calculate it from appropriately supported flow and actual event durations. Include air-saving restarts and rejected attempts. Preserve the measurement instrument, configured reference state, valid observation period and missing intervals. A totaliser already measuring the complete ejector assembly should not have its internal functions added a second time.

Repeat representative cycles under the agreed demanding conditions, including acceptable workpiece variation and concurrent users. Retain distributions and exceptions, not only the mean. The number of cycles and acceptance thresholds belong to the approved test plan; this page does not invent a universal sample size or reliability claim.

After changes to cups, tool mass, trajectory, tubing, source pressure, firmware or release settings, reassess the affected requirements. Preserve the original result and configuration. A revised production recipe can change acceleration and duty even when no pneumatic hardware has been replaced.

20. Diagnose the symptom before increasing vacuum or supply pressure

A failed pickup should be described by the observed event and boundary. “Vacuum low” is incomplete without the location, time and motion state. Determine whether the pressure never reached the target, reached it too late, fell during acceleration or appeared satisfactory while the workpiece slipped. These symptoms lead to different investigations.

These are hypotheses, not proven root causes. The same pressure trace can arise from different combinations of source flow and leakage. A new vacuum threshold can make a dashboard look favourable without improving contact or response. Keep the evidence needed to distinguish causes, then choose the smallest justified correction.

Retest the complete affected cycle after a correction. Improving evacuation can increase production rate and simultaneity; changing a release pulse can disturb adjacent parts; a larger cup can change compliance. The final measure is an accepted handling outcome with an accountable air demand, not a single improved number.

21. Worked example 1: total theoretical force passes, but one cup bank does not

All geometry, loads and factors in this example are fictional. A rigid workpiece has a mass of 12 kg. Four cups lift it from above with upward acceleration of 3.0 m/s². The example uses g = 9.81 m/s² and an explicitly assumed design factor of 2.0. Each cup is assigned an effective circular diameter of 45 mm. This is a teaching effective area, not a nominal supplier diameter. Atmospheric pressure is assumed to be 100 kPa absolute and cup pressure 40 kPa absolute.

The available pressure difference is 60 kPa. Effective area per cup is π × 0.045²/4 = 0.001590431281 m². Theoretical normal contribution per cup is 60,000 × 0.001590431281 = 95.425877 N. Four cups therefore provide 381.703507 N in total. The design demand for the stated vertical case is 2 × 12 × (9.81 + 3.0) = 307.44 N. A total-only comparison shows a nominal surplus of 74.263507 N.

Now examine the layout. There are two banks, each containing two cups, separated by 0.40 m. The centre of gravity is offset by 0.10 m toward one bank from the midpoint. Assume a rigid workpiece, no additional moment and equal sharing within each bank. Static equilibrium for the factored vertical demand gives R_near = W × (0.5 + e/L) and R_far = W × (0.5 − e/L).

The aggregate force was not the governing result. The near bank fails the stated comparison even though total available force exceeds total demand. Increasing the near-bank effective diameter to 55 mm raises its theoretical contribution to 285.099533 N, but does not establish cup material compatibility, available footprint, workpiece stiffness or permissible contact loading. Those questions remain open.

Two further changes show why the duty must remain explicit. If the same four 45 mm contacts are used on a vertical face and the fictional friction coefficient is 0.35, supporting the same factored vertical demand would require 307.44/0.35 = 878.40 N of normal contribution in the simplified shear model. The earlier normal total is inadequate. This is a separate illustrative load case, not a combined-load approval.

If local atmospheric pressure were 85 kPa absolute while cup pressure remained 40 kPa absolute, the pressure difference would fall to 45 kPa. Four 45 mm effective cups would then provide only 286.277631 N. The unchanged 307.44 N demand would exceed even the total contribution. A common absolute cup pressure does not create a common holding force at every atmospheric condition. Neither altered case can be accepted by carrying forward the original green total.

22. Worked example 2: a flow-basis mistake changes predicted evacuation time

Assume a fictional rigid connected vacuum volume of 2.0 L, initially at 100 kPa absolute, with a target of 40 kPa absolute. Temperature is constant and initially leakage is neglected. There is no valve or sensor delay in the following evacuation-only calculations. The example intentionally compares different flow assumptions rather than different real ejectors.

First, suppose the effective actual pumping speed at the evacuated volume is a constant 6.0 L/s over the complete pressure range. The logarithmic model gives t = (2/6) × ln(100/40) = 0.305430244 s. At the target pressure, this actual pumping speed corresponds to only 6 × 40/100 = 2.4 reference L/s at the stated equal-temperature 100 kPa reference.

Second, suppose the removal rate is instead a constant 6.0 reference L/s at 100 kPa throughout the event. The reference gas quantity removed is 2 × (100 − 40)/100 = 1.2 L. The constant-reference-flow calculation gives 1.2/6 = 0.200000 s. The difference is not a rounding error. The two models describe different mass-removal histories. Entering “6 L/s” without its reporting basis cannot resolve which prediction is appropriate.

Now use a third, explicitly discrete teaching model. Suction rates below are assumed representative reference flows within each pressure band; leakage is assumed constant at 0.5 reference L/s. The same 100 kPa reference and equal-temperature condition apply. Each 20 kPa pressure decrease removes 2 × 20/100 = 0.4 reference L from the vessel.

The late portion now dominates because net removal is smaller. This is a piecewise approximation using fictional rates, not a manufacturer curve integration or a guaranteed upper/lower time bound. A real model needs supported pressure-dependent data, installation losses, temperature behaviour and a defensible treatment of leakage.

If an alternative's final-band suction were 0.4 reference L/s while ingress remained 0.5, its net removal would be negative. The worksheet must flag the target as not reached under the assumed band model. It must not divide by −0.1 and report a negative evacuation time, and it must not replace the weak final-band value with the catalogue maximum at atmospheric suction pressure.

Contact time, command delay, pressure distribution and the confirmation dwell must be added on their own defined basis when assessing overall pickup. The example's 0.387013 s is an evacuation-only estimate; it is not a setting for a machine timer or permission to start transfer.

23. Worked example 3: air-saving duty reduces volume, not automatically station kWh

A fictional ejector consumes 60 reference L/min whenever vacuum generation is active at its stated supply condition. A separate release function consumes 90 reference L/min for 0.12 s per completed cycle. The selected teaching reference is dry air at 100 kPa absolute and 293.15 K. All flow values in this example use that same basis. The machine completes ten cycles per minute, with a six-second cycle period.

In the baseline case, generation is active for a 4.50 s handling window each cycle. Motive volume is 60 × 4.50/60 = 4.50 L; release volume is 90 × 0.12/60 = 0.18 L. Total consumption is 4.68 reference L per cycle, or 46.8 reference L/min at ten completed cycles per minute. No other standby or pilot consumption is assumed in this fictional baseline.

In the air-saving case, logged generation intervals are an initial 0.45 s evacuation and two restart pulses of 0.18 s and 0.15 s. Total on-time is 0.78 s. Generation uses 0.78 reference L, and the unchanged release uses 0.18 L. Total becomes 0.96 reference L per cycle, or 9.6 reference L/min.

The difference is 3.72 L per cycle, a 79.487179% reduction against this particular baseline. The number comes from the stated timings, not from a supplier's advertised saving. It remains dependent on maintaining the required holding and release performance. A more porous workpiece, worn seal or different transfer duration can change the restart pattern and invalidate the assumed on-time.

For 4,000 actual production hours at the stated rate, the reference-volume difference is (46.8 − 9.6)/1,000 × 60 × 4,000 = 8,928 m³. That is an air-volume result. No electricity saving, tariff benefit or carbon reduction is assigned because station response and energy evidence have not been supplied.

Now include unsuccessful attempts. Across 1,000 accepted picks, suppose twenty additional failed attempts each use 0.80 reference L, including their own recovery air. Total consumption is 1,000 × 0.96 + 20 × 0.80 = 976 L. Consumption per accepted pick is 0.976 L, not 0.96 L. The denominator and rejected-attempt boundary must remain visible.

For four identical cells, average demand is 4 × 9.6 = 38.4 L/min. Four simultaneous generation events require 240 L/min, while four simultaneous release events require 360 L/min under the stated constant-flow assumptions. These are separate scheduled events here; they are not added as simultaneous unless the sequence allows that overlap. Average consumption does not establish the necessary supply-path capacity.

24. Worked example 4: leakage, control delay and reservoir volume interact

All conditions are fictional. A rigid vacuum region of 3.0 L is isolated for a controlled observation while the workpiece is safely supported. Its absolute pressure rises from 30 kPa to 45 kPa over 3.0 s. Temperature is assumed constant and equal to the 100 kPa reference temperature. There is no change of contact shape or connected volume in the model.

Equivalent reference ingress is q_leak,ref = 3 × (45 − 30)/(100 × 3) = 0.15 L/s, or 9.0 L/min. The result is the total equivalent ingress associated with the observed pressure rise, not a located leak. A thermal transient or deforming cup would require a different interpretation.

A proposed air-saving cycle stops generation at 35 kPa absolute and restarts at 45 kPa absolute. Under the same constant-ingress model, off-time between those thresholds is 3 × (45 − 35)/(100 × 0.15) = 2.0 s. The pressure-rise rate is 5.0 kPa/s. If there is 0.20 s from crossing the restart threshold until effective net removal begins, pressure rises another 1.0 kPa to 46 kPa absolute.

Assume a separate illustrative process limit of 50 kPa absolute. The remaining modelled interval from 46 to 50 kPa is 0.80 s. Sensor uncertainty, filtering, varying leakage, position changes and fault conditions have not been included. The calculation therefore does not prove that the response margin is adequate. The actual limit itself requires a mechanical and process basis.

If the connected volume is doubled to 6.0 L while ingress remains unchanged, the off-time across 35 to 45 kPa doubles to 4.0 s. But initial evacuation also changes. With a fictional constant effective actual pumping speed of 6.0 L/s and no leakage for this separate initial-evacuation comparison, the time from 100 to 35 kPa is 0.524911 s for 3 L and 1.049822 s for 6 L. The reservoir trade-off cannot be judged from off-time alone.

Finally, if effective suction after restart is assumed constant at 0.75 reference L/s while ingress remains 0.15 L/s, net removal is 0.60 L/s. Returning the original 3 L region from 46 to 35 kPa requires 3 × 11/100 = 0.33 reference L to be removed, giving 0.55 s. This is another declared approximation, not a controller simulation. A real ejector's changing suction characteristic and installed pressure trace must govern the final response assessment.

25. Editable gripper-duty, ejector-comparison and verification records

The following three records are manually editable in Word and supplied as structured templates in the developer package. They organise evidence; they are not automatically calculating spreadsheets or equipment-control forms. Replace the entry prompts with actual project information and retain the source and revision. Empty fields mean unresolved information, not zero load, zero leakage or approval.

Record A — Gripper duty and workpiece definition

Record B — Ejector and air-consumption comparison

Record C — Trial, acceptance and controlled changes

Complete the records in sequence. Record A defines the required result. Record B determines whether a candidate has the evidence to address it. Record C documents what the installed arrangement actually demonstrated. Do not let a later favourable test silently change the earlier requirement; issue a controlled requirement revision when the intended duty genuinely changes.

For an enquiry, supply the workpiece description, contact layout, motion and cycle requirements, current ejector details, tubing, supply conditions, symptom and any available traces. Customer drawings and production records remain private unless separately authorised. The completed worksheet supports a technical discussion; it does not establish inventory, supplier authorisation or a guaranteed service turnaround.

26. Frequently asked engineering questions

Is maximum vacuum the most important ejector selection figure?

No single maximum completes the selection. The gripper needs adequate pressure difference at the contacts, while the ejector needs sufficient suction throughout evacuation and at the leakage condition. A maximum-vacuum point can occur with little remaining suction flow. Keep the workpiece, effective area, target, connected volume, curve and timing together. The useful comparison is at the required duty, not simply at the deepest catalogue vacuum.

Is suction flow the same as compressed-air consumption?

No. Suction flow is gas removed from the vacuum circuit. Motive-air consumption is the compressed air used to drive an ejector. They belong to different boundaries and may use different reporting states. An electric pump still has suction flow but does not create the same motive-air demand. Store the quantity type and reference condition with each value before doing any addition or energy calculation.

Can the total cup area establish the safe load?

It can support a theoretical pressure-force calculation, but not a complete safe-load determination. Effective area, pressure difference, load distribution, acceleration, friction, moments, workpiece stiffness and contact behaviour must all be addressed. A favourable total can hide an overloaded cup bank. The actual permissible load and protective measures require the applicable supplier data and responsible machine design, not just the total from F = ΔpA.

Why does a gripper work on one carton but fail on another?

The supplied workpieces may differ in permeability, surface coating, seams, damage, stiffness or contact geometry. These differences can change leakage and the ability of the cups to form a seal. Compare representative parts and the actual cup-pressure trace rather than assuming that a common product name establishes identical duty. A larger ejector may not resolve deformation or a contact crossing an open seam.

Does air saving always improve the application?

It can reduce motive-air on-time when the circuit holds vacuum sufficiently between generation intervals, but the result depends on leakage, thresholds, delay and required pressure stability. Frequent restart events or continuous fallback can reduce the benefit. Holding and release requirements must still be met. Report the actual event-volume difference and successful production denominator instead of transferring an advertised percentage to every workpiece.

Can a vacuum tank solve a slow or unreliable pickup?

A connected volume can increase modelled pressure-rise time under a fixed leakage assumption, but it also adds volume to evacuate. Its benefit depends on topology, isolation, starting condition and the generator's response. It cannot prevent every contact failure or workpiece rupture.

Why is the sensor reading better at the ejector than at the cup?

During flow, the connecting path can create a pressure difference. Filters, tubing, fittings and valves may separate the generator from the contact. A sensor can also be isolated from a failed branch. Confirm where it measures and what region its result represents. Pair the reading with the actual handling event and local evidence before using it as permission for movement.

Can an ejector be sized from average machine consumption?

Average consumption supports plant-air accounting but does not establish evacuation response or simultaneous supply demand. A cell with a low cycle-average flow may require much higher motive flow while generation or blow-off is active. Use the event profile and actual source characteristics for the supply path. Keep suction-side response calculations separate from compressor-side average and peak demand.

Should release air be added to the ejector consumption figure?

Add it when the stated ejector figure excludes the release function and release uses separately supplied air. Do not add it again when a measured or supplier-defined complete-cycle quantity already includes that path. Record the boundary, flow basis and event duration. Failed attempts, recovery and standby can also belong in the reporting scope, particularly when consumption is expressed per accepted pick.

What evidence is needed before changing thresholds or motion speed?

Retain the approved handling requirement, exact configuration, supplier limits, workpiece variation, cup-pressure behaviour and timing evidence. A faster trajectory can increase force and moment demands; a weaker-vacuum threshold can reduce holding contribution; a changed restart delay can consume response margin. Review the affected duties and use an authorised trial. A favourable worksheet result is not permission to alter a live machine or bypass its safeguards.