FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Complete Specification
(See section 10 and rule 13)
An Electromechanical Hoist With Fault Detection System
Mahindra and Mahindra Limited
Indian company registered under the Indian Companies Act, 1956
Gateway Building, Apollo Bunder, Mumbai – 400001, Maharashtra, India
The following specification particularly describes the invention and the manner in which it is to be performed.

An Electromechanical Hoist With Fault Detection System
Field of Invention:
The present invention relates to an electromechanical material handling device, which is used for lifting components, assemblies in workshops/factories. In particular, the present invention relates to the hoist concerns detecting and stopping uncontrolled movement of the hoist.
Background of invention:
An electric hoist is an electromechanical material handling device which is typically used for lifting components, assemblies in any workshop / factories. An electric hoist has a motor which is made to rotate in forward /reverse directions which via mechanical transmission results in the movement of component lifted in up/down direction. Normally an operator pendant is attached to the control panel of hoist. When the operator presses the up/down push button, corresponding movement starts and continues till that button is kept pressed. As soon as the push button is released, an electromechanical brake is applied to stop downward movement due to the gravitational forces.
In conventional pendants, a green button is used to start the movement & red button is used to switch “OFF” control in case of emergency. Control panel of any conventional hoist has 3 contactors: main, forward and reverse. The main contactor is always switched on except when power is switched off or the

emergency switch on the pendant is pressed. There is an electrical interlock between forward and reverse contactors so that they don’t become “ON” simultaneously. Hoist may have chain or rope and lifting tackle. Hoist is normally mounted on Gantry or rail.
There are a number of ways in which the conventionally operated hoists fail:
1. Push button getting stuck: In this event the movement will continue in up or down direction. In up direction same will be cut off by upper limit switch but part at topmost height has a risk of falling down. This may lead to an accident.
2. Contactor getting stuck: In this event the movement will continue in up or down direction similar to last failure mode but in up direction same can’t be now cut off by upper limit switch. Hence motor keeps on rotating and risk of part falling down is more likely. This may lead to an accident.
3. Load slippage: As explained earlier, a conventional hoist has electromechanical brakes. A brake comes into picture when the motor is off (“NO” movement commanded)—this will stop the load coming down due to the gravitational load. Due to frequent operations of a brake, the brake shoe liner wears out. Under these conditions, the hoist load will start slipping. If operator is not aware of this situation then the hoisted load may suddenly come down and cause an accident.

4. Overloading: A hoist is rated for fixed capacity. If operator lifts weight more than capacity of hoist then rope starts getting stretched. With frequent usage the rope may get damaged and may cause an accident.
5. Excess loading: Sometimes operator tries to lift dead-weights like clamped fixtures or very heavy loads. In that case there is an extreme danger of Hoist falling down from gantry. In such cases there can be fatal accident.
The existing hoists suffer from the above mentioned potential drawbacks. There is therefore a need for an electromechanical hoist which overcomes these drawbacks.
Objects of invention:
Accordingly, it is an object of the present invention to provide an electromechanical hoist in which the potential failure modes are detected automatically and a preventive response is actuated.
Brief Description of Figures:
Figure 1 – a perspective view of a typical hoist
Figure 2 – a perspective view of a typical control device for hoists
Figures 3-6 – Logic diagram for the hoist control of the invention
Figure 7 shows the schematic of the internal workings of the hoist of the present
invention

Figure 7A shows the schematic of external inputs to the hoist of the present
invention
Figure 8 shows a schematic of the conventional hoist
List of parts:
1 – electromechanical hoist 11 – voltage regulator
2 – control device 12 – filter
3 – Programmable Logic Controller 13 – Opto isolator circuit (PLC) or a microcontroller 14 – driver circuit
4 – load cell control section 15 – relay
5 – failure indicator 16 – operational amplifier
6 – power supply section 17 – bracket
7 – push button 18 – motor coupling
8 – contactor 19 – load cell
9 – proximity switch 20 – hook
10 – rectifier
Summary and brief description of invention:
The present invention discloses an electromechanical hoist with a control unit which allows it to detect the possible failure modes such that the operator may take necessary steps to prevent failure. The invention thus comprises an electromechanical hoist with purpose built programmable logic controller (PLC) and related specially developed hardware. The present invention thus provides an

electromechanical hoist in which the potential failure modes are detected automatically before the hoist is actually operated to lift loads and a preventive response is actuated in the case failures are detected.
Detailed description of the invention:
The invention is an electromechanical hoist (1) with a control device (2) (also termed as a fault detection unit) which has an intelligent logic. By the use of the invention, the potential failure modes of an industrial hoist are detected automatically and a preventive response is actuated.
The invention comprises a control device (2) and a logic that runs on a purpose-built hardware. Figure 7 shows the circuit schematic for the hoist of the invention and Figure 7A shows various inputs to the hoist. Figures 7 and 7A thus show parts of a conventional hoist along with a Programmable Logic Controller (PLC) (or, alternatively referred to as a microcontroller) (3), a load cell control section (4), and a failure indicator (5). The PLC (3) has the facility to receive digital input as well as analog input. The output from the PLC (3) (in digital format) is sent to the failure indicator (5). For the purpose of the description, the term PLC (3) is used, however, it will be taken to mean PLC or microcontroller. The term logic controller block (or simply logic controller) is also taken to mean a part of the invention that includes a PLC or a microcontroller.

The functional blocks shown in Figure 7 include a power supply section (6) that supplies power to the logic controller block (6). (The logic controller block incorporates the PLC and the other enabling circuitry.) The load cell section (4) provides analog input to the logic controller (6). The logic controller (6) receives digital input from the push buttons (7), the contactors (8), and the proximity switch (9). The logic controller (6) sends a digital output to the failure indicator (5).
As also shown in Figure 7, the power supply section has a rectifier (10), a voltage regulator (11), and a filter (12). There's an Opto isolator circuit (13) placed between the microcontroller and the push buttons/contactors/proximity switch. A driver circuit (14) and a relay (15) is provided to send the digital output to the failure indicator. The rectifier (10) converts AC supply into DC (which is required by different components in the electronic circuitry). The filter (12) removes ripples resulting from conversion of the AC voltage component into the DC voltage. The Opto isolator circuit (13) isolates the PLC/microcontroller (3) from external inputs so that any short circuit in external input components (like push button) does not damage the microcontroller (3) which is heart of system. The driver circuit (14) helps switch ON/ Off the load (e.g. a relay, or lamps). The microcontroller (3) controls outputs based on change in status of inputs from push buttons/contactors/proximity switch and the load cell (19) and the associated logic programmed within the microcontroller (3) itself. There's also an operational amplifier (16) (OPAMP) that compares the analogue input voltage signal with

reference value (or the set value), amplifies the error in order to give a signal to the microcontroller (3). The relay (15) operates on command from the microcontroller (3). The function of the relay (15) is to control the contactors to cut off power to hoist motor in case of abnormalities (e.g. when the hoist attempts to lift more weight than the set limit) – such relays are not present in the conventional hoists.
As shown in Figure 1, a hoist is equipment that is used to move around objects, particularly large and heavy ones. A typical hoist therefore has an arrangement by which it can lift or bring down or move sideways a heavy object. Hoists are used in industrial and manufacturing environment to facilitate movements of parts and equipment from one place to another. A pendant (see Figure 2) having a number of pushbuttons; these typically comprise 'start', and 'stop' buttons, to start and stop the operations, respectively, and 'up' and 'down' buttons to move loads up and down, respectively.
The control device (2) of a hoist has a built-in Programmable Logic Controller (PLC) circuit, which is connected to the push buttons (7) or other operational devices that the hoist operator uses to control the hoist movements. In one embodiment, the hoist operator's pendant's push buttons are connected to the PLC (2) as an input, so that any movement command given from pendant by the operator is also sensed by PLC. The main contactor (which in turn routes the

electricity to the reverse and forward contactors) now is controlled through the output of PLC.
At the start of the hoist operation, if no fault is detected, the PLC sets the main contactor to an “ON” position when it is commanded with ‘Control On’ input (pressing of a button that is typically green in colour). The upward/downward movement is sensed by a proximity switch which is mounted on a bracket (not shown) near the motor coupling (not shown). Hence any motor rotation generates proximity pulses that are given as input to the PLC. Upon receiving the proximity pulses, PLC understands that the motor is rotating and therefore the coupled load is moving (either in the upward or downward direction). Each of the three contactors (main, forward, and reverse) is also provided with a ‘Normally Open’ (“NO”) contact. The “NO” contact of each of the three contactors feed an input to the PLC. When any contactor is switched “ON”, the closure of the respective “NO” contact will confirm “ON” status in PLC. Thus PLC knows when any of the three contactors are actually switched “ON”.
As shown in Figure 7A, a load cell (19), which is a strain gauge transducer, is typically mounted between the hoist and the hook (20) for lifting load. It can also be mounted between the hoist and the gantry but in that case the weight of hoist will add to the load and setting of the load cell controller will need to be adjusted accordingly. Whenever the load is lifted by the hoist, a strain (equivalent to the amount by which the load lifted) is developed, which is converted by a transducer

(not shown) into an electrical signal (typically measured in mv (milivolts)). The electrical signal is sent to the load cell controller which in turn compares it with reference signal (overload weight limit). If the amount of strain sensed by the load cell (19) is found to exceed the reference value, the load cell (19) sends a signal to the PLC indicating that the hoist is attempting to lift more load than allowed.
The manner in which the PLC identifies various failure modes is now discussed.
1. Push button Getting Stuck: This is defined as a contactor staying in an “ON” position for an unacceptable length of time. For example, the Up or Down button input to the PLC may remain stuck (remains on “ON”) for more than, say, 8 seconds continuously which is considered more than usual length of average operation time. This means that while the push button is not operable, a movement continues, which is dangerous. Under these circumstances, the PLC will receive proximity pulses confirming the uncontroled movement. Also, the PLC will receive input from the forward or the reverse contactor (the “NO” contact being closed). Thus PLC will ascertain that the push button has become stuck and cut off the output from the main contactor, consequently switching off the control to stop hoist movement immediately. Also the PLC will make audio visual indication “ON” on a failure indicator (5) for warning the hoist operator of hazard and a failure mode.
2. Contactor Getting Stuck: In this case the Up or Down button input to the PLC is neither stuck nor does it remain pressed (“ON”), but still the PLC receives

proximity pulses confirming movement. Also the PLC receives input from forward or reverse contactor (“NO” contact close). Thus PLC concludes that the contactor has become stuck and then cuts off the output from the main contactor, consequently switching off control to stop hoist movement immediately. Also the PLC will provide an audio visual indication on the failure indicator (5) for warning the hoist operator of hazard and failure mode.
3. Load Slippage: PLC under this circumstance will neither receive any input from forward/reverse push buttons nor from the contactors. Only input coming to the PLC will be from the proximity switch which is due to the movement. Thus PLC will identify the slippage of load and give an audio or visual (or an audio-visual) indication on the failure indicator as a warning to the operator of hazard and failure mode. In this case it is not possible to arrest the down ward movement of load but operator is made aware so that he can safeguard himself.
4. Overload / Excess Load: In this case the load cell comes into picture. A conventional hoist is unable to detect the overload (i.e. the hoist attempting to lift more weight than allowed) whereas the present invention with a load cell (19) along with controller gives output signal to the PLC. In this case the PLC will cut off main contactor to stop lifting of load and will give an indication of it to the operator.

As is evident from Figures 3-6, the logic of the present invention overcomes all possible known modes of failure of hoist and allows the hoist to be operated safely.
As the part of the fault detection process, the programmed logic of the invention checks whether the Up/Down push button has been pressed (see Figure 3). If it determines affirmatively, it checks whether it has been pressed for less than a normal duration of pressing (say 8 seconds). If it has been, it checks whether the Up/Down contactor has become stuck. If yes, it checks whether there are rotation pulses of proximity. If yes, it checks whether the lifted weight is more than the capacity. If yes, it sends a signal of failure mode due to overweight to the hosit controller panel.
If Up/Down push button is not pressed, the logic checks for failure due to contactor stuck mode (see Figure 4).
If Up/Down push button has been pressed for 8 seconds or more, the logic checks for failure by Push button stuck mode (see Figure 5).
If the Up/Down contactor is not on, it checks for wiring or faulty contactor.
If there are no rotation pulses of proximity detected, then it raises alert for faulty wiring/motor/coupling or faulty proximity detector.

If Up/Down push button hasn't been pressed, the logic checks whether the Up/Down contactor has got stuck (see Figure 4). Depending on the route the logic has taken to arrive at the decision of determining that the Up/Down push button has not got stuck (routes A or B as depicted in Figure 3), the logic determines whether the contactor has become stuck or the push button has become stuck. If the Up/Down push button has not been pressed (route A), the possibility is that of Up/Down button remaining turned on and rotation pulses of proximity being detected, both of which suggest a contactor being stuck. If the contactor button has been pressed but more than or equal to 8 seconds (route B), then again the contactor might appear to remain stuck or the rotation pulses of proximity may get detected, however, this time this is due to the Up/Down push button being stuck (rather than the contactor). Finally, during route A, if the rotation pulses of proximity are detected, it suggests failure of break liners. If, on the other hand, the rotation pulses are not detected, it suggests the normal more, i.e. there is no fault.
The logic presented here is quite intricate and innovative and the circuit developed to put it in practice quite inventive.
As is evident from the foregoing discussion, the following advantages of the invention are apparent over the existing hoists:
1. Existing hoists do not have any warning systems to warn the operator of the possible failures of various functional systems of a hoist. The present

invention provides a systematic approach to identify various modes in which a hoist might fail and to provide warnings.
2. The present invention prevents a hoist from attempting to lift weights that are greater than design weights.
3. The present invention identifies uncontrolled movement of the lifted weight due to malfunctioning (due to sticking) of push buttons or contactors.
4. The present invention identifies uncontrolled movement of the lifted weight due to slippage (worn out breaks etc.). Although the present invention does not stop the slippage, a warning about slippage allows the operator to move out of the way of the slipping load.
It is also evident from the foregoing discussion that the present invention discloses the following embodiments:
1. An electromechanical hoist with a fault detection system characterised in that said fault detection system it comprises a logic controller device for detecting potential failure modes and preventing associated failures, and a failure indicator wherein said logic controller unit assesses the safety status of the hoist which is indicated on the indicator.
2. An electromechanical hoist as described in embodiment 1 wherein the said failure indicator comprises individual displays for displaying the safety

status of said hoist for push button, contactor, load slippage, and overloading.
3. An electromechanical hoist as described in embodiments 1 and 2 wherein said logic controller device further comprises a power supply unit, a load cell control unit and a logic controller, wherein said logic controller is capable of receiving analog signals from said load cell unit and digital input from push buttons, or contactors, or proximity sensors that monitor the movement of the hoist.
4. An electromechanical hoist described in embodiments 1 to 3, wherein said electric power supply unit comprises a rectifier, a voltage regulator and a filter, wherein said rectifier converts AC electric supply into a DC supply, said filter removes ripples resulting from conversion of the AC voltage component into the DC voltage, and said voltage regulator maintains the voltage of the converted DC supply.
5. An electromechanical hoist described in embodiments 1 to 4, wherein said fault detection unit further comprises an Opto isolator circuit to isolate said microcontroller unit from power surge and a driver input and a relay.
6. An electromechanical hoist described in embodiments 1 to 5 wherein in the instance of a push button that operates the hoist getting stuck, or becoming inoperable otherwise, the PLC sends a warning signal to the failure indicator.

7. An electromechanical hoist described in embodiments 1 to 6, wherein in the instance of a contactor getting stuck, or becoming otherwise inoperable, the PLC sends a warning signal to the failure indicator.
8. An electromechanical hoist described in embodiments 1 to 7, wherein in the instance of said hoist attempting to lift a load greater than what said hoist is designed for, the PLC sends a warning signal to the failure indicator.
9. An electromechanical hoist described in embodiments 1 to 8, wherein in the instance of there being an uncontrolled slippage of hoisted load, the PLC sends a warning signal to the failure indicator.
While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

We claim:
1. An electromechanical hoist with a fault detection system characterised in that said fault detection system it comprises a logic controller device for detecting potential failure modes and preventing associated failures, and a failure indicator wherein said logic controller unit assesses the safety status of the hoist which is indicated on the indicator.
2. An electromechanical hoist as claimed in claim 1 wherein the said failure indicator comprises individual displays for displaying the safety status of said hoist for push button, contactor, load slippage, and overloading.
3. An electromechanical hoist as claimed in claims 1 and 2 wherein said logic controller device further comprises a power supply unit, a load cell control unit and a programmable logic controller, wherein said programmable logic controller is capable of receiving analog signals from said load cell unit and digital input from push buttons, or contactors, or proximity sensors that monitor the movement of the hoist.
4. An electromechanical hoist as claimed in claims 1 to 3, wherein said electric power supply unit comprises a rectifier, a voltage regulator and a filter, wherein said rectifier converts AC electric supply into a DC supply, said filter removes ripples resulting from conversion of the AC voltage component into the DC voltage, and said voltage regulator maintains the voltage of the converted DC supply.

5. An electromechanical hoist as claimed in claims 1 to 4, wherein said fault detection unit further comprises an Opto isolator circuit to isolate said microcontroller unit from power surge and a driver input and a relay.
6. An electromechanical hoist as claimed in claims 1 to 5 wherein in the instance of a push button that operates the hoist getting stuck, or becoming inoperable otherwise, the programmable logic controller sends a warning signal to the failure indicator.
7. An electromechanical hoist as claimed in claims 1 to 6, wherein in the instance of a contactor getting stuck, or becoming otherwise inoperable, the programmable logic controller sends a warning signal to the failure indicator.
8. An electromechanical hoist as claimed in claims 1 to 7, wherein in the instance of said hoist attempting to lift a load greater than what said hoist is designed for, the programmable logic controller sends a warning signal to the failure indicator.
9. An electromechanical hoist as claimed in claims 1 to 8, wherein in the instance of there being an uncontrolled slippage of hoisted load, the programmable logic controller sends a warning signal to the failure indicator.