- Gripper safety requires verification of both holding the load when required and preventing release when safety conditions are not met. These correspond to holding capacity and release authorization.
- Constrain routine release through the load state machine (S0–S8). Execute it only in S6, Release Permitted; software and hardware block routine release in S1–S5 and S8.
- Seating requires height, position, support contact and load transfer together. Confirming load transfer (Fs/W ≥ η for at least τ) checks the support available after release.
- Pneumatic interlocks, vacuum retention, load retention after air loss, pressure/vacuum monitoring, dual buttons and fault lockout provide defense in depth against different failure paths. Set each threshold from project risks and test data.
Organization: Jiangsu AUREK Intelligent Technology Co., Ltd. · Engineering Research Center (Lianyungang, Jiangsu) · Document type: Corporate engineering research white paper · Version: V1.1. This article supports the design, design review and acceptance validation of custom handling grippers. Thresholds and example parameters illustrate the method; the actual configuration is determined by the workpiece, operating conditions, risk assessment and validation records. Download the full PDF from the upper-right corner or the end of the article.
00Abstract
During gripping, lifting, transport, positioning and release, a custom handling gripper must both maintain its hold on the workpiece and control when that hold is removed. If the workpiece is suspended, not yet stable on its support or not yet fully transferred to that support, accidental button operation or pneumatic/vacuum faults can cause unintended release, a dropped load or equipment damage. Release safety must therefore be designed and validated separately from load capacity.
This article organizes release control around a load-state model. Height, position, support contact and load transfer form the release permissive, supported by pneumatic interlocks, vacuum retention, air-loss protection, dual buttons, press-and-hold confirmation, fault lockout and multiple-sensor evaluation to ensure no release in an unauthorized state. It includes variable definitions, configuration points for different grippers, FMEA, test matrices and acceptance checklists. Project risk assessment and measured data determine thresholds, test counts and acceptance criteria; the examples demonstrate the analysis method.
01Introduction
1.1 Research Background
Grippers used in machining, automotive components, battery modules, sheet metal and heavy-load logistics require structures, sensors and control logic matched to workpiece shape, mass, surface, cycle time and equipment conditions. Alongside load-capacity checks, the release phase requires separate assessment: removing the hold can still cause loss of control while the workpiece is suspended or has contacted a support without transferring its load. The design must define the logical relationship between establishing support and authorizing release.
1.2 Holding Capacity and Release Control
Gripping and holding capacity demonstrate that the load can be securely acquired and retained. Release authorization and state control prevent opening under unsafe conditions. Failure of either can cause loss of load control, so both must be validated separately.
1.3 Application Scope
This article covers prevention of unintended release and confirmation of load placement for mechanical jaws, vacuum grippers, electro-permanent magnets and combined tooling. In a project, relate the method to the consequences of workpiece failure, handling movements, personnel access, control architecture and relevant standards. Complete project and equipment risk assessments and any required functional safety calculations and validation. Third-party certification follows its applicable procedures separately.
02Inadvertent-Release Risks and Control Objectives
2.1 Definition of Inadvertent Release
Unintended release means opening the jaws, depressurizing, breaking vacuum, demagnetizing, applying release blow-off or otherwise reducing holding force before safe release conditions are met. Unlike gripping failure caused by insufficient holding capacity, the defining issue is that the release action occurs in an unauthorized state. Control must check load state, release permissive, operator intent and the safety chain together to prevent release in mid-air, before stable placement or during an abnormal state.
2.2 Inadvertent-Release Risk Categories
| No. | Risk type | Typical situation | Main control measures |
|---|---|---|---|
| R1 | release while suspended | The load is still suspended and the release valve or clamp unclamping mechanism receives a release request. | State machine blocking, placement/transfer confirmation, pneumatic or electrical release interlock |
| R2 | Release before the load is fully seated | The load has contacted the support surface, but the support is insufficient or the weight has not been transferred | Contact force confirmation, load transfer confirmation, stabilization time determination |
| R3 | Accidental Release Request | Accidental button press, HMI input or maintenance operation | Two-button control, press-and-hold confirmation, access control and logs |
| R4 | Unclamping After Air Loss | The compressed-air supply is interrupted and the pressure is lower than the threshold, causing the clamping force to decrease. | Normally closed/self-locking design, check valve, pressure-holding valve, air receiver and pressure switch |
| R5 | Loss of Vacuum Retention | Vacuum leakage, suction-cup failure, or interruption of the compressed-air supply reduces the vacuum level | Vacuum reservoir, vacuum switch, check valves, independent circuits and pressure-loss lockout |
| R6 | Incorrect Sensor Decision | Height, position, contact or load sensors affected by contamination, drift, shock | Multisource fusion, 2oo3 voting, self-diagnostics and fault lockout |
Table 1 Risk classification and main control measures for accidental release
2.3 Top-Event Logic
Taking "unexpected load loss of support" as the top event T, the main cause path can be described by the following formula:
Eair denotes release while suspended; Eunstable denotes release before stable seating; Epressure denotes reduced holding force from pressure or vacuum faults; Econtrol denotes control faults or operator error. Any critical path can cause the top event, so use a combination of state constraints, sensor confirmation, hardware interlocks and failure protection.
03Load State Model
3.1 Need for a State Model
The state model relates a release request to the actual stage of load handling. A pressed button or active release-position signal must be followed by confirmation that the load is placed, stable and transferred to its support. The control logic constrains release accordingly: release may occur only in the authorized release state.
3.2 State Definitions
| State | Name | meaning | release constraints |
|---|---|---|---|
| S0 | No load | Fixture not holding workpiece | No loaded-release action; prevent unintended motion |
| S1 | Clamping confirmation | The workpiece is clamped, vacuum-held or magnetically held but not yet lifted | Release prohibited outside controlled pickup/placement or maintenance procedures |
| S2 | lifting | The workpiece leaves the pickup surface and enters the lift | Inhibit release |
| S3 | Transfer | The workpiece moves with the fixture and is suspended or held by the fixture | Inhibit release |
| S4 | Approach and placement | The workpiece is lowered toward the target support area | Inhibit release |
| S5 | Load Transfer | The workpiece contacts the support surface and the load is transferred from the fixture to the support surface. | Release prohibited until transfer is complete and stable |
| S6 | Release Permitted | Positioning, support, load transfer and safety chain conditions are met | The only normal release-permissive state |
| S7 | Release completed | The clamp is released and the load is borne by the support structure | The release action ends and the exit or reset process is entered. |
| S8 | Fault Lockout | Loss of pressure, vacuum abnormality, sensor inconsistency, emergency stop or logic abnormality detected | Release prohibited; maintain support or complete safe handling before controlled reset |
Table 2 Load state definition and release constraints
3.3 State-Transition Principles
In the formula, State(t) is the current state, Sensor(t) is the sensor signal set, Logic(t) is the state machine and release permission logic, and Safety(t) is the safety chain signal such as emergency stop, safety door, safety PLC or safety relay. Normal operations can proceed along S0→S1→S2→S3→S4→S5→S6→S7. In any state, if abnormal pressure, vacuum, sensor contradiction, communication abnormality, emergency stop or safety chain disconnection is detected, S8 abnormal lock should be entered. State advancement should rely on sufficient sensing evidence; when the evidence is insufficient, it should stay in the current state or enter the safe side state.
04Release-permissive logic and control architecture
4.1 Multi-condition "AND" logic
Use a multi-condition AND for release: height, position, contact, load transfer, operator request, safety chain and fault-free status must all be valid. No single sensor, button or software variable may independently trigger release.
4.2 Four-Factor Release Permission
R is release permission. Hs confirms height; Ls confirms horizontal position and orientation; Ps confirms support contact; Os confirms load transfer. All four must be true. Height cannot replace load transfer, position cannot replace contact, and an operator request cannot replace safety confirmation.
4.3 Final Release-Command Synthesis
For routine release, State = S6 is required. Operator_Request is the request after safeguards against accidental operation; Safety_OK denotes a valid safety chain. No_Fault excludes lockout, sensor faults, insufficient pressure/vacuum and unauthorized maintenance bypass. Enable the release valve through a safety output, pilot permission or hardware interlock, with feedback diagnostics and fault-injection verification.
4.4 Dual-Channel Permissive Architecture and Diversity
Rsensor is the physical sensing-channel decision; Rlogic is the state-machine and control-logic decision, including S6 confirmation for routine release. Use diverse sensing principles where practicable. A sensing channel may combine height, support-side weighing and pressure/vacuum switches; the logic channel checks state, sequence, time windows and the safety chain. Disagreement inhibits release and generates diagnostic information.
4.5 Separation of Software and Hardware Responsibilities
Divide release control into four stages—software permission, hardware enable, valve actuation and actuation-feedback confirmation—and provide diagnostics at each stage. Software manages the state machine, signal fusion, diagnostics and records. Hardware interlocks continue to block unauthorized release if software issues an erroneous request.
05Seating and Load-Transfer Confirmation
5.1 Height Confirmation
H is measured height; Hset is target seating height; ΔH is the deviation; EH is the tolerance selected for positioning accuracy, support geometry and sensor repeatability. Height shows proximity to the target, but does not independently establish that the support carries the load.
5.2 Position and Orientation Confirmation
X, Y and θ are measured horizontal position and orientation. X0, Y0 and θ0 are targets; EX, EY and Eθ are tolerances. Check Z position, locating-pin engagement or pallet location where required. Verify that the load lies within the effective support area, including partial support, eccentric loading and overturning risk.
5.3 Support-Contact Confirmation
Fc represents detected support contact force or the defined contact signal; Fmin is its minimum effective threshold. Set Fmin above noise, vibration and unloaded drift, using unloaded and loaded tests.
5.4 Load-Transfer Confirmation (Core Criterion)
Load-transfer confirmation checks whether the support structure has taken the workpiece weight. This directly addresses the support available after gripping is removed; reaching the correct height alone cannot provide that evidence.
W is design load, m workpiece mass, g gravitational acceleration and az the vertical design acceleration; use 0 for static calculation and include dynamic effects for impact, rapid descent or emergency stopping. Fg is the load held by the tooling and Fs the load carried by the support. During seating, Fs increases and Fg decreases. Os confirms transfer. Select η, often starting from 0.85–0.95, through validation; τ filters transient impact and oscillation. For multiple supports or long workpieces, also check individual load distribution and overturning, for example Fsi ≥ Fsi,min at each critical support and support moments |Mx| and |My| within their limits.
5.5 Multisource Fusion and Confidence
Support-side weighing, gripper-side pressure/force sensing, changes in lifting-axis current, changes in cup vacuum and contact switches can jointly provide evidence of load transfer. Critical decisions should cross-check signals from at least two different physical principles.
In the formula, 2oo3 represents a two-out-of-three vote, that is, the conclusion is adopted only when at least two of the three independent judgment signals are confirmed to be valid (the occasional failure of a sensor can be tolerated, but it does not replace sensor diagnosis and project risk assessment); Si is the normalized result of the i-th sensor or decision channel, wi is the weight, C is the comprehensive credibility, Cth is the credibility threshold. Weights and thresholds should be determined experimentally and their basis documented.
5.6 Combined Seating Criterion
Height, position, contact and load transfer must all be satisfied. Transfer_OK is a necessary condition; insufficient transfer evidence requires release inhibition.
06Pneumatic, vacuum and fail-safe design
6.1 Interlock Layers
Configure unintended-release prevention as three layers of defense in depth: mechanical, electrical/safety control, and pneumatic/vacuum circuits. The mechanical layer provides self-locking or travel limits, the electrical layer determines state and issues safety outputs, and the pneumatic/vacuum layer blocks unauthorized release within the actuation circuit.
6.2 Pneumatic Release Interlock
This logic means the release-valve pilot or enable circuit may actuate only when the complete release permissive is true, the safety chain is valid, and no fault is present. Do not reduce the interlock to Position_OK, because position alone does not prove load transfer. Use a valve-manifold design that maintains gripping or inhibits release after loss of power or air. If standard PLC outputs coexist with safety outputs, control the release-valve energy path with a safety output or safety relay; use the standard output only for the operator request or motion command.
6.3 Loss-of-Air Protection and Pressure Retention
After an air-supply fault, the system must keep the load controlled and follow the designed safe-stop, controlled-lowering or fault-lockout sequence. Air-loss protection does not authorize continued normal handling.
- Grippers should use a normally closed, self-locking, or mechanically wedged structure so that loss of air or power does not actively release the load.
- Install a check valve, pressure-holding valve, or locking valve on the clamping or vacuum chamber to reduce the rate of abnormal pressure loss.
- Where necessary, provide an air receiver or energy-storage unit, with clearly defined holding time, minimum pressure, and response strategy.
- The pressure switch should be an independent hardware input to the release-inhibit chain. If pressure falls below the threshold, release must be inhibited and an alarm generated.
- Pressure-retention capability must be validated through leakage, holding-time, and minimum-gripping-force tests; the mere presence of a valve does not establish that the safety requirement is met.
6.4 Vacuum Retention and Vacuum-Release Control
Vacuum tooling must address loss of holding force from low vacuum and premature vacuum-break or blow-off commands. Vacuum-break, blow-off and exhaust-valve actions require S6 permission, just as mechanical unclamping does.
- Provide a vacuum switch or sensor to monitor whether the vacuum level meets the gripping-permission and handling-retention thresholds.
- Use a vacuum reservoir, check valves, and segmented circuits to reduce the effect of a single-point leak on all suction cups.
- Leak testing should cover static retention, handling acceleration, suction-cup aging, and variation in workpiece surface condition.
- The vacuum-break/blow-off release valve must be governed by Release permission. Unauthorized bypass in maintenance or commissioning mode is prohibited.
- The vacuum holding time, vacuum drop rate and alarm threshold should be determined on a project basis; if indicators such as "the drop rate does not exceed 10% within 30 s" are used, they should be supported by test records.
6.5 Abnormal-State Lockout and Reset
Fault lockout S8 includes motion inhibition, alarms, state recording and controlled reset. After reset, recheck load state, pressure/vacuum, sensor consistency and operating authorization; release capability must not resume directly.
07Release Protection for Different Tooling Types
7.1 Mechanical-Gripper Tooling
Mechanical grippers mainly rely on form fit, clamping force and friction to hold the workpiece. For vertical handling conditions that rely on friction to maintain, the clamping force can be checked as follows:
n is the number of effective friction surfaces, μ the worst-case friction coefficient and FN the normal force per surface. K is the safety factor; m, g and az retain their earlier meanings. Check sliding and overturning under horizontal acceleration, eccentricity and impact. Provide normally closed/self-locking retention, grip and opening feedback, pressure monitoring, air-loss holding and release-valve interlocks. For form-fit tooling, verify engagement depth, locating pins and locks as well as cylinder position.
7.2 Vacuum Tooling
Fvac is available vacuum holding force, ΔP the vacuum pressure difference and Aeff the effective suction area. λ accounts for cup compression, surface condition, leakage and orientation. S is the holding margin; Favailable uses the worst-case vacuum and effective area, while Frequired includes weight, acceleration, orientation and disturbance. Set Smin from project risk assessment. Permit lifting only after the vacuum threshold is reached, monitor vacuum during transfer, and enter holding/alarm/safe-response procedures on low vacuum. Vacuum-break release requires S6. Check remaining capacity after cup, branch or vacuum-source failure.
7.3 Magnetic Tooling (Electro-Permanent Magnet)
Electro-permanent magnetic grippers use electrical power for magnetization or demagnetization and can generally retain magnetic force after power is removed. They are suitable for magnetizable materials. Design checks must cover poor contact, changing air gaps, material variation, incorrect interpretation of residual magnetism and accidental demagnetization, as well as power-loss behavior.
Fmag is effective magnetic holding force under the worst air gap, material and contact conditions. Verify values using sample tests or valid supplier data. Include magnetization feedback, holding-force or contact confirmation, release permission for demagnetization, maintenance access control and a response plan after abnormal power loss.
7.4 Comparison of Tooling Types
| Gripper Type | Holding Principle | Main failure modes | Key points to prevent accidental release |
|---|---|---|---|
| Mechanical Gripper | Clamping force, friction, form fit | Air-loss unclamping, insufficient force, slip or incomplete locking | Normally closed/self-locking, pressure monitoring, opening feedback, release valve interlock |
| Vacuum Handling | Pressure difference between inside and outside of suction cup | Leakage, aging of the suction cup, vacuum breaking malfunction, defective surface | Vacuum monitoring, reservoir, check valves, segmented circuits and vacuum-break permission |
| Electro permanent magnet | Magnetic circuit holding force | Poor fit, material differences, false triggering of demagnetization, misjudgment of residual magnetism | Magnetization/demagnetization state control, holding-force confirmation and access control |
| Combination fixture | Combined holding principles | Single retention mode failure, logic switching error | Clarify the primary/auxiliary hold relationship, and maintain at least one effective hold when switching |
Table 3: Holding principles, failure modes and key points to prevent accidental release of various tooling units
08Ergonomics and misuse protection
Dual buttons, press-and-hold operation and interface prompts reduce accidental input, while the state machine, sensor confirmation and hardware interlocks jointly control the release permissive. If the release permissive is false, the system must reject release even when requested by the operator.
8.1 Two-Button and Press-and-Hold Confirmation
B1 and B2 are independent button inputs. Tsync is the synchronization window, Tpress the continuous press duration and Thold the hold threshold. Select Tsync and Thold for cycle time, ergonomics and risk. Where a safety performance level is required, use suitably rated inputs and a corresponding safety-control architecture.
8.2 HMI Secondary Confirmation and Status Indication
The HMI displays release inhibition, approaching placement, load transfer, release permission and fault lockout, with confirmation at critical stations. It supports visibility and traceability; it cannot bypass S6, R, Safety_OK or No_Fault for routine release.
8.3 Maintenance Mode and Access Control
Manage maintenance release, manual vacuum breaking and manual demagnetization through access permissions, key switches, low-speed/jog operation, area clearance and operating logs. Maintenance mode should retain load-support detection or confirmation of manual fixture support wherever practicable, preventing bypass operations from introducing unintended release.
09FMEA risk analysis
The table below demonstrates how to organize an FMEA for unintended-release prevention. Project scores are assessed from workpiece mass, personnel exposure, cycle time, failure history, diagnostic coverage and measured data. The example scores are not measured project results.
| failure mode | main reason | Consequences | S/O/D/RPN | control measures | Verification points |
|---|---|---|---|---|---|
| release while suspended | State machine error, release valve malfunction, bypass uncontrolled | Falling load, equipment damage, personnel risk | 10/3/4/120 | S1～S5 inhibit release; safety interlock on the release valve; S6 is the sole release-permissive state | Request release while suspended; verify no valve actuation and record the alarm |
| Release before the load is fully seated | Correct height but insufficient support, eccentric loading or incomplete transfer | Tipping, slipping, fixture or workpiece damage | 9/4/4/144 | Contact confirmation, load transfer confirmation, stabilization time, eccentric load monitoring | Test seating tolerances, eccentric loads and partial support; verify unsafe conditions do not receive permission |
| Unclamping After Air Loss | Main compressed-air supply interruption, pipeline leakage, valve leakage | Reduced holding force and loss of load control | 10/2/5/100 | Normally closed/self-locking retention, check valve, pressure-holding valve, pressure switch and air receiver | Cut off the air supply and measure the holding time, minimum pressure and clamping force |
| Vacuum pressure loss | Suction cup leakage, abnormal vacuum source, surface contamination | The vacuum holding force decreases and the load drops. | 10/3/4/120 | Vacuum tank, one-way valve, vacuum monitoring, partitioned circuit, pressure loss lock | Simulate leakage rates and verify alarm, holding and release inhibition |
| Release by accidental touch | Single button accidental touch, HMI misclick, maintenance misoperation | Unexpected release request enters the system | 8/5/3/120 | Double button, long press, secondary confirmation, permission management | Single button, short press, and unauthorized operation shall not trigger Release. |
| Sensor misjudgment | Contamination, drift, cable failure, reflection or vibration | Incorrect confirmation of seating or transfer | 8/4/4/128 | Multi-source fusion, 2oo3, self-diagnosis, signal consistency check | Inject disconnection, short-circuit and drift faults; verify inhibition or lockout |
| Software or communication abnormality | Program defects, communication delays, variable writing errors | Release-permissive logic error or state inconsistency | 10/2/5/100 | Safety PLC, watchdog, dual-channel permissive, version control | Communication outages, watchdog timeouts, and version regression testing |
Table 4. FMEA for Inadvertent-Release Prevention (Illustrative Scores)
Prioritize hardware interlocks and test validation for high-RPN items or severity 9–10. Retain periodic validation and maintenance checks for high-severity failures after risk-reduction measures.
10Test methods and acceptance items
10.1 Validation Principles
Use boundary-condition, fault-injection and repeatability tests to assess release inhibition, unsafe false-positive decisions and fault diagnostics. Retain traceable records stating sample, cycle count, task conditions, abnormalities and statistical method. Report release counts and fault-free cycles from actual testing.
10.2 Functional and Interlock Test Matrix
| test category | Test method | expected result | Acceptance record |
|---|---|---|---|
| Status blocked | Send release requests one by one in S1~S5 | Release is not established, the release valve does not operate, and the system gives the prohibition reason. | Record status, request, valve output, alarm information |
| allow release | Send a release request when all S6 conditions are met | The release actions are executed in sequence, and S7 is entered after the release is completed. | Record Hs/Ls/Ps/Os, safety chain, action feedback |
| Pneumatic interlock | Send a normal release command after disconnecting the pilot permissive or safety output | The release valve has no action and the air path remains blocked. | Record pilot pressure or valve position feedback |
| safety chain | Trigger emergency stop, safety door or safety relay disconnection | Immediately inhibit release; maintain clamping or perform safe disposal if necessary | Record safety-chain inputs and state transitions |
| Abnormal reset | Create conflicting sensor signals or insufficient pressure, then reset | After reset, all diagnostic and permissive conditions must be re-established; direct release is prohibited. | Record fault codes, the person performing the reset and reset conditions |
Table 5: Function and interlock test matrix
10.3 Seating and Load-Transfer Tests
| Item | Test method | Acceptance Criteria |
|---|---|---|
| height confirmed | Tested separately at target height, boundary height and out-of-tolerance height | Height_OK is only allowed if the height is within the threshold; rejected if it exceeds the tolerance. |
| location confirmation | Set working conditions such as X/Y/orientation deviation, positioning pin not entering, pallet offset, etc. | Position_OK is false when the deviation exceeds the limit or the positioning is not in place. |
| Contact confirmation | Set up contact, light contact, no contact and sensor noise working conditions | Inhibit release if contact force is below Fmin or the signal is unreliable |
| Load Transfer | Measure transfer ratio using weighing, gripper side force or current trends | Fs/W reaches η and lasts for τ before setting Transfer_OK |
| Unbalanced load/multi-point support | Creating a single suspended point, excessive load on one side or abnormal support point | Inhibit release when eccentric loading exceeds its limit, even if total support force is sufficient |
| Unsafe False-Positive Decision | Count the number of false permissions for all working conditions that should be rejected | Unsafe false permissions: 0. Record and review conservative rejections. |
Table 6: Placement and load transfer tests
10.4 Loss-of-Air, Pressure-Loss, and Holding Tests
| Item | Test method | Record content | Acceptance concerns |
|---|---|---|---|
| loss-of-air retention | Shut off the compressed-air supply at rated load | Pressure curve, clamping force, holding time, state transfer | Holding duration meets safe-response needs; no unclamping |
| slow leak | Artificially set up small leaks and continuously monitor them | Pressure/vacuum drop rate, alarm time, lock time | Alarm thresholds are appropriate and the trend is diagnosable. |
| rapid loss of pressure | Disconnect main air or vacuum source | Valve position, pressure, load status, alarm | System goes into hold/lock, no release allowed |
| Restore compressed-air supply | After the abnormality, restore the compressed-air supply and try the operation | Whether it is necessary to reset and whether to re-confirm the status | Restoration must not automatically release the load or clear the fault. |
Table 7. Air-Loss, Pressure-Loss and Holding Tests
10.5 Human-Factor Incorrect-Operation Tests
| Test items | Test method | expected result |
|---|---|---|
| single button | Just press B1 or B2 | Release is not established |
| Asynchronous press | Press the buttons more than Tsync apart | Release is not established |
| Short press | duration less than Thold | Release is not established |
| Maintenance release without permission | Unauthorized user performs manual release or vacuum breaking | Deny the operation and log it |
| Allow release prompt | Operator performs release at S6 | Clear status indication and correct sequence of actions |
Table 8. Tests of Safeguards Against Incorrect Operation
10.6 Documentation and Acceptance Outputs
- Risk-assessment and FMEA records;
- calculations for gripping force, vacuum holding force, or magnetic holding force;
- release-permissive logic diagram, state-machine diagram, and safety I/O list;
- pneumatic, vacuum, and electrical schematics with interlock descriptions;
- test records, fault-injection records, and abnormal-reset records;
- maintenance-inspection items and a periodic pressure-retention/leakage validation plan;
- operating instructions and maintenance-mode access-control instructions.
11Engineering Design Checklist
| Category | Check items | Acceptance criteria |
|---|---|---|
| Clamping capacity | Clamping/vacuum gripping/magnetic force calculation | The most unfavorable working condition parameters are adopted, and the safety factor and basis are clear |
| Clamping capacity | Dynamic load considerations | Consider additional loads caused by lifting, lowering, emergency stops, swings or impacts |
| Placement confirmation | Height and location confirmation | The threshold basis is clear and the boundary test is passed |
| Placement confirmation | Support contact confirmation | The contact signal is greater than the noise and drift, and the failure can be diagnosed |
| Load Transfer | Transfer ratio confirmation | Fs/W reaches the project threshold η and maintains τ; multi-point support eccentric load is controlled |
| release logic | Four-Factor Permission | R = Hs ∧ Ls ∧ Ps ∧ Os, single point substitution is not allowed |
| release logic | final command synthesis | State = S6, Operator_Request, R, Safety_OK and No_Fault are simultaneously true |
| Pneumatic interlock | pilot permissive | The full permission chain enables the release valve; loss of power or air inhibits release |
| Air-supply shutoff protection | Pressure Retention and Load Holding | Documented holding time after air loss meets the safe-response requirement |
| Vacuum system | Vacuum monitoring and leakage prevention | Complete range of vacuum switches/sensors, vacuum tanks, check valves and leak tests |
| Ergonomics | Dual button/long press/permissions | Single-point accidental touch, short press, and unauthorized operation cannot trigger the release. |
| Corrective Action | Abnormal lock and reset | S8 fully documented with lockout, fault codes, controlled resets and operations |
| Verification information | Testing and Traceability | Complete methods, samples, criteria, raw records and documented issue closure |
Table 9 custom handling tooling anti-accidental release engineering design checklist
12Engineering conclusion
Acceptance separately verifies holding capacity and release control. The state machine constrains routine release, which is permitted only in S6. Software and hardware block routine release in S1–S5 and S8.
Placement confirmation requires height, position, support contact and load transfer to be satisfied together. Check the support available after opening using load-transfer evidence, then address the relevant failure paths with pneumatic interlocks, vacuum retention, load retention after air loss, pressure/vacuum monitoring, dual buttons, press-and-hold operation and fault lockout.
Set thresholds, synchronization windows, hold times, transfer ratios and safety factors from project risk assessment, sample testing and acceptance records. Apply state-based safety control throughout gripping, transport, placement and release to establish design and acceptance requirements that can be inspected and tested.
