A method of controlling a medicament delivery device

Abstract

A method of controlling a medicament delivery device, the method comprising the following steps with the following order: receiving a value of a predetermined moving speed of a plunger rod of the medicament delivery device; receiving a value of a predetermined moving distance of the plunger rod; moving the plunger rod with the predetermined moving speed; detecting a reaction force received by the plunger rod; measuring an expelled volume by the plunger rod when the detected reaction force is lower than a predetermined value; stopping measuring the expelled volume by the plunger rod when detected reaction force is higher than the predetermined value; calculating a value of a distance with the measured expelled volume by the plunger rod and the value of the predetermined moving speed of the plunger rod; stopping the movement of the plunger rod when the plunger rod has moved the calculated distance and the predetermined moving distance.

Description

[0001] TITLE

[0002] A method of controlling a medicament delivery device

[0003] TECHNICAL FIELD

[0004] The present disclosure generally relates to a method of controlling a medicament delivery device, and particularly to a method comprising the steps of detecting a reaction force received by the plunger rod.

[0005] BACKGROUND

[0006] Medicament delivery devices such as pen-type manual injectors or auto-injectors are generally known for self-administration of a medicament by patients without formal medical training. For example, patients suffering from diabetes may require repeated injections of insulin, or patients may require regular injections of other types of medicaments, such as growth hormones.

[0007] It is an advantage when the medicament delivery devices for self-administration comprise automatic functions so that even if users are without professional training or are in an emergency situation, the users can easily and properly use the medicament delivery devices.

[0008] Even though many of the devices on the market, as well as the ones described above, have their respective advantages, there is still room for improvement.

[0009] SUMMARY

[0010] The invention is defined by the appended claims, to which reference should now be made.

[0011] In the present disclosure, when the term “distal direction” is used, this refers to the direction pointing away from the dose delivery site during use of the medicament delivery device. When the term “distal part / end” is used, this refers to the part / end of the delivery device, or the parts / ends of the members thereof, which under use of the medicament delivery device is / are located furthest away from the dose delivery site. Correspondingly, when the term “proximal direction” is used, this refers to the direction pointing towards the dose delivery site during use of the medicament delivery device. When the term “proximal part / end” is used, this refers to the part / end of the delivery device, or the parts / ends of the members thereof, which under use of the medicament delivery device is / are located closest to the dose delivery site.

[0012] Further, the term “longitudinal”, “longitudinally”, “axially” or “axial” refer to a direction extending from the proximal end to the distal end, typically along the device or components thereof in the direction of the longest extension of the device and / or component.

[0013] Similarly, the terms “transverse”, “transversal” and “transversally” refer to a direction generally perpendicular to the longitudinal direction. Further, the terms “circumference”, “circumferential”, or “circumferentially” refer to a circumference or a circumferential direction relative to an axis, typically a central axis extending in the direction of the longest extension of the device and / or component. Similarly, “radial” or “radially” refer to a direction extending radially relative to the axis, and “rotation”, “rotational” and “rotationally” refer to rotation relative to the axis.

[0014] There is hence provided a method of controlling a medicament delivery device, the method comprising the following steps with the following order: receiving a value of a predetermined moving speed of a plunger rod of the medicament delivery device; receiving a value of a predetermined moving distance of the plunger rod; moving the plunger rod with the predetermined moving speed; detecting a reaction force received by the plunger rod; measuring an expelled volume by the plunger rod when the detected reaction force is lower than a predetermined value ; stopping measuring the expelled volume by the plunger rod when detected reaction force is higher than the predetermined value; calculating a value of a distance with the measured expelled volume by the plunger rod and the value of the predetermined moving speed of the plunger rod; stopping the movement of the plunger rod when the plunger rod moves further the calculated distance after moved the predetermined moving distance.

[0015] Preferably, according to another embodiment, the steps of measuring an expelled volume by the plunger rod and stopping measuring the expelled volume by the plunger rod when detected reaction force is higher than the predetermined value further comprises the following steps in the following order: measuring a time lapse when the detected reaction force is lower than a predetermined value; when detected reaction force is higher the predetermined value, stopping measuring the time lapse.

[0016] Preferably, according to another embodiment, the steps of measuring an expelled volume by the plunger rod and stopping measuring the expelled volume by the plunger rod when detected reaction force is higher than the predetermined value further comprises the following steps in the following order: measuring a moving distance of the plunger rod when the detected reaction force is lower than a predetermined value; when detected reaction force is higher the predetermined value, stopping measuring the moving distance

[0017] Preferably, according to another embodiment, the medicament delivery device comprises a stepping motor; and wherein the step of moving the plunger rod with the predetermined moving speed further comprises the following step: moving the plunger rod by rotating the stepping motor.

[0018] Preferably, according to another embodiment, the medicament delivery device comprises a stepping motor.

[0019] Preferably, according to another embodiment, the step of detecting a reaction force received by the plunger rod further comprises the following steps with the following order: measuring the back EMF value of the rotating stepping motor; and determining the reaction force received by the plunger rod by calculating the change of the measured back EMF value.

[0020] Preferably, according to another embodiment, before the steps of as described in any one of the above embodiments, the method further comprises the following steps with the following order: receiving a value of a volume of the medicament container; receiving a value of a volume of air in the medicament container; and calculating a value of feree of the plunger rod that can compress the volume of the air to a volume lower than 5% of the volume of the medicament container.

[0021] Preferably, according to another embodiment, the step of moving the plunger rod with the predetermined moving speed further comprises the following step: moving the plunger rod to apply the calculated value of feree to the medicament container with the predetermined moving speed.

[0022] Preferably, according to another embodiment, the step of moving the plunger rod to apply the calculated value of feree to the medicament container with the predetermined moving speed comprises the following steps in the following order: detecting the reaction force received by the plunger rod; and moving the plunger rod with the predetermined moving speed with a predetermined force for a medicament delivery operation if the detected reaction force is fewer than a second predetermined value.

[0023] Preferably, according to another embodiment, after the step of stopping the movement of the plunger rod, the method further comprises the following step: moving the plunger rod reversely with a reverse speed; wherein the reverse speed is greater than the predetermined moving speed of the plunger rod.

[0024] A second aspect of the invention further provides a processor of a drive unit of a medicament delivery device, wherein the drive unit comprises a stepping motor; wherein the processor being configured to perform the method according to any of the preceding embodiments.

[0025] A third aspect of the invention further provides a drive unit of a medicament delivery device comprising: a stepping motor, a plunger rod operably connected to the stepping motor, and the processor according to above-mentioned embodiment; wherein the processor being electrically connected to the stepping motor, and wherein the plunger rod is configured to be driven by the stepping motor when the stepping motor is rotating.

[0026] Preferably, according to another embodiment, the drive unit comprises a housing configured to receive a cassette of a medicament delivery device, the cassette being releasably attached to the housing; and wherein the plunger rod is configured to be moved into a medicament container within the cassette.

[0027] Preferably, according to another embodiment, the plunger rod is connected to the stepping motor via a lead screw. Preferably, according to another embodiment, the stepping motor is rotatable around the lead screw within the housing. The stepping motor is engaged with the lead screw via a threaded engagement. A switch is arranged within the housing. Upon activation of the switch, the rotation of the stepping motor around the lead screw is configured to move the lead screw proximally so that a stopper of a medicament container in the cassette is moved by the lead screw.

[0028] Preferably, according to another embodiment, the stepping motor is the stepping motor.

[0029] Preferably, according to another embodiment, the motor comprises a rotor and a channel extending through the rotor. The lead screw is partially positioned within the channel.

[0030] Preferably, according to another embodiment, the channel comprises a thread extending around the channel. The thread is engaged with the thread of the lead screw.

[0031] Alternatively, according to another embodiment, the drive unit comprises a connector operably connected to the rotor such that the connector is configured to be rotated by the rotor.

[0032] Preferably, according to another embodiment, a channel extends through the connector and is aligned with the channel of the rotor along the longitudinal axis.

[0033] Preferably, according to another embodiment, the channel of the connector comprises a thread extending around the channel of the connector. The thread is engaged with the thread of the lead screw.

[0034] Preferably, according to another embodiment, the connector is attached to the rotor.

[0035] Preferably, according to another embodiment, the connector and the rotor are made of different materials.

[0036] Preferably, according to another embodiment, the connector is made of plastic.

[0037] Preferably, according to another embodiment, the rotor is made of metal.

[0038] Preferably, according to another embodiment, the longitudinal axis is the central axis of the motor.

[0039] Preferably, according to another embodiment, an engagement formed between the plunger rod and the inner wall of the housing is a ribs-ribs engagement or a ribs-grooves engagement.

[0040] Preferably, according to another embodiment, an engagement formed between the lead screw and the inner wall of the housing is a ribs-ribs engagement or a ribs-grooves engagement.

[0041] Preferably, according to another embodiment, the distal end of the lead screw comprises a polygonal cross-section perpendicular to the longitudinal axis and the inner wall of the housing comprises a polygonal cross-section perpendicular to the longitudinal axis. Preferably, according to another embodiment, the stepping motor is configured to reciprocate the movement of the lead screw.

[0042] Preferably, according to another embodiment, the drive unit comprises a second switch accommodated within the housing.

[0043] Preferably, according to another embodiment, the second switch is aligned with the distal end of the lead screw in the direction of the longitudinal axis.

[0044] Preferably, according to another embodiment, the second switch is positioned distally away from the distal end of the lead screw.

[0045] Preferably, according to another embodiment, the second switch is configured to be switched by the distal end of the lead screw when the lead screw is moved distally relative to the stepping motor such that when the second switch is switched the motor is stopped.

[0046] Preferably, according to another embodiment, the second switch is a non-contact switch.

[0047] Alternatively, according to another embodiment, the second switch is configured to be switched by being pushed in the distal direction relative to the housing by the distal end of the lead screw.

[0048] Preferably, according to another embodiment, the second switch comprises a flipping arm.

[0049] Preferably, according to another embodiment, the second switch is configured to be switched when the flipping arm is pivoted by the distal end of the lead screw.

[0050] Preferably, according to another embodiment, the housing extends along the longitudinal axis between a proximal end and a distal end.

[0051] Preferably, according to another embodiment, the housing comprises a fixture at a proximal portion of the housing.

[0052] Preferably, according to another embodiment, the fixture is configured to be releasably attached to a counter fixture of the cassette of the medicament delivery device.

[0053] Preferably, according to another embodiment, the fixture and the counter fixture form a bayonet connection or a thread connection.

[0054] Preferably, according to another embodiment, the switch is a non-contact switch.

[0055] Alternatively, according to another embodiment, the switch is operably movable by a component of the cassette of the medicament delivery device when the cassette is attached to the housing between an active position where the switch is activated and an inactive position where the third switch is deactivated. Preferably, according to another embodiment, the medicament container of the medicament delivery device is a syringe, a cartridge or a collapsible bag.

[0056] Preferably, according to another embodiment, the medicament container of the medicament delivery device is made of glass material or plastic material.

[0057] Preferably, according to another embodiment, the medicament container of the medicament delivery device is accommodated within the cassette.

[0058] Preferably, according to another embodiment, the medicament delivery device is an injection device, an inhalation device, or a medical sprayer.

[0059] Preferably, according to another embodiment, the injection device is configured to perform a subcutaneous injection, intramuscular injection, or intravenous injection.

[0060] Preferably, according to another embodiment, the medicament delivery device is an auto-injector.

[0061] Preferably, according to another embodiment, the medicament delivery member is an injection needle or a spray nozzle.

[0062] Preferably, according to another embodiment, the medicament delivery member is accommodated in the cassette.

[0063] Preferably, according to another embodiment, the cassette is configured to be fully received within the housing of the drive unit.

[0064] Preferably, according to another embodiment, the cassette is configured to be partially received within the housing of the drive unit.

[0065] Preferably, according to another embodiment, the cassette comprises an information tag containing the predetermined moving speed of a plunger rod and / or the predetermined moving distance of the plunger rod and / or the volume of the medicament container; and wherein the drive unit comprises an information reader configured to read the information tag of the cassette.

[0066] Preferably, according to another embodiment, the information tag is one of an RFID chip, NFC chip, barcode, and QR code.

[0067] Preferably, according to another embodiment, the information tag is attached to an outer surface of a body of the cassette.

[0068] Preferably, according to another embodiment, the information tag is embedded in the body.

[0069] Preferably, according to another embodiment, the information tag is attached to the medicament container. Preferably, according to another embodiment, the information tag is a flexible sheet.

[0070] Preferably, according to another embodiment, the body having a counter fixture releasably attached to the fixture of the housing of the drive unit and a delivery member cover.

[0071] Preferably, according to another embodiment, the body extends along an axis between a proximal end and a distal end.

[0072] Preferably, according to another embodiment, a delivery member cover is telescopically relative to a proximal end of the body between an extended position where the delivery member cover protrudes from the proximal end of the body in the direction of the axis and a retracted position.

[0073] The medicament delivery devices described herein can be used for the treatment and / or prophylaxis of one or more of many different types of disorders. Exemplary disorders include, but are not limited to: rheumatoid arthritis, inflammatory bowel diseases (e.g. Crohn’s disease and ulcerative colitis), hypercholesterolaemia, diabetes (e.g. type 2 diabetes), psoriasis, migraines, multiple sclerosis, anaemia, lupus, atopic dermatitis, asthma, nasal polyps, acute hypoglycaemia, obesity, anaphylaxis and allergies. Exemplary types of drugs that could be included in the medicament delivery devices described herein include, but are not limited to, small molecules, hormones, cytokines, blood products, antibodies, antibody-drug conjugates, bispecific antibodies, proteins, fusion proteins, peptibodies, polypeptides, pegylated proteins, protein fragments, protein analogues, protein variants, protein precursors, chimeric antigen receptor T cell therapies, cell or gene therapies, oncolytic viruses, or immunotherapies and / or protein derivatives. Exemplary drugs that could be included in the medicament delivery devices described herein include, but are not limited to (with non-limiting examples of relevant disorders in brackets): etanercept (rheumatoid arthritis, inflammatory bowel diseases (e.g. Crohn’s disease and ulcerative colitis)), evolocumab (hypercholesterolaemia), exenatide (type 2 diabetes), secukinumab (psoriasis), erenumab (migraines), alirocumab (rheumatoid arthritis), methotrexate (amethopterin) (rheumatoid arthritis), tocilizumab (rheumatoid arthritis), interferon beta-1 a (multiple sclerosis), sumatriptan (migraines), adalimumab (rheumatoid arthritis), darbepoetin alfa (anaemia), belimumab (lupus), peginterferon beta-1 a' (multiple sclerosis), sarilumab (rheumatoid arthritis), semaglutide (type 2 diabetes, obesity), dupilumab (atopic dermatitis, asthma, nasal polyps, allergies), glucagon (acute hypoglycaemia), epinephrine (anaphylaxis), insulin (diabetes), atropine and vedolizumab (inflammatory bowel diseases (e.g. Crohn’s disease and ulcerative colitis)) , ipilimumab, nivolumab, pembrolizumab, atezolizumab, durvalumab, avelumab, cemiplimab, rituximab, trastuzumab, ado-trastuzumab emtansine, fam-trastuzumab deruxtecan- nxki, pertuzumab, transtuzumab-pertuzumab, alemtuzumab, belantamab mafodotin-blmf, bevacizumab, blinatumomab, brentuximab vedotin, cetuximab, daratumumab, elotuzumab, gemtuzumab ozogamicin, 90-Yttrium-ibritumomab tiuxetan, isatuximab, mogamulizumab, moxetumomab pasudotox, obinutuzumab, ofatumumab, olaratumab, panitumumab, polatuzumab vedotin, ramucirumab, sacituzumab govitecan, tafasitamab, or margetuximab. Pharmaceutical formulations including, but not limited to, any drug described herein are also contemplated for use in the medicament delivery devices described herein, for example pharmaceutical formulations comprising a drug as listed herein (or a pharmaceutically acceptable salt of the drug) and a pharmaceutically acceptable carrier. Pharmaceutical formulations comprising a drug as listed herein (or a pharmaceutically acceptable salt of the drug) may include one or more other active ingredients, or may be the only active ingredient present.

[0074] Exemplary drugs that could be included in the medicament delivery devices described herein include, but are not limited to, an immuno-oncology or bio-oncology medications such as immune checkpoints, cytokines, chemokines, clusters of differentiation, interleukins, integrins, growth factors, enzymes, signaling proteins, pro-apoptotic proteins, anti-apoptotic proteins, T-cell receptors, B-cell receptors, or costimulatory proteins.

[0075] Exemplary drugs that could be included in the medicament delivery devices described herein include, but are not limited to, those exhibiting a proposed mechanism of action, such as HER-2 receptor modulators, interleukin modulators, interferon modulators, CD38 modulators, CD22 modulators, CCR4 modulators, VEGF modulators, EGFR modulators, CD79b modulators, Trop-2 modulators, CD52 modulators, BCMA modulators, PDGFRA modulators, SLAMF7 modulators, PD-1 / PD-L1 inhibitors / modulators, B-lymphocyte antigen CD19 inhibitors, B-lymphocyte antigen CD20 modulators, CD3 modulators, CTLA-4 inhibitors, TIM-3 modulators, VISTA modulators, INDO inhibitors, LAG3 (CD223) antagonists, CD276 antigen modulators, CD47 antagonists, CD30 modulators, CD73 modulators, CD66 modulators, CDw137 agonists, CD158 modulators, CD27 modulators, CD58 modulators, CD80 modulators, CD33 modulators, APRIL receptor modulators, HLA antigen modulators, EGFR modulators, B-lymphocyte cell adhesion molecule modulators, CDw123 modulators, Erbb2 tyrosine kinase receptor modulators, mesothelin modulators, HAVCR2 antagonists, NY-ESO-1 0X40 receptor agonist modulators, adenosine A2 receptors, ICOS modulators, CD40 modulators, TIL therapies, or TCR therapies.

[0076] Exemplary drugs that could be included in the medicament delivery devices described herein include, but are not limited to, a multi-medication treatment regimen such as AC, Dose-Dense AC, TCH, GT, EC, TAC, TC, TCHP, CMF, FOLFOX, mFOLFOX6, mFOLFOX7, FOLFCIS, CapeOx, FLOT, DCF, FOLFIRI, FOLFIRINOX, FOLFOXIRI, IROX, CHOP, R-CHOP, RCHOP-21 , Mini-CHOP, Maxi-CHOP, VR-CAP, Dose-Dense CHOP, EPOCH, Dose-Adjusted EPOCH, R- EPOCH, CODOX-M, IVAC, HyperCVAD, R-HyperCVAD, SC-EPOCH-RR, DHAP, ESHAP, GDP, ICE, MINE, CEPP, CDOP, GemOx, CEOP, CEPP, CHOEP, CHP, GCVP, DHAX, CALGB 8811 , HIDAC, MOpAD, 7 + 3, 5 +2, 7 + 4, MEC, CVP, RBAC500, DHA-Cis, DHA-Ca, DHA-Ox, RCVP, RCEPP, RCEOP, CMV, DDMVAC, GemFLP, ITP, VIDE, VDC, VAI, VDC-IE, MAP, PCV, FCR, FR, PCR, HDMP, OFAR, EMA / CO, EMA / EP, EP / EMA, TP / TE, BEP, TIP, VIP, TPEx, ABVD, BEACOPP, AVD, Mini-BEAM, IGEV, C-MOPP, GCD, GEMOX, CAV, DT-PACE, VTD-PACE, DCEP, ATG, VAC, VelP, OFF, GTX, CAV, AD, MAID, AIM, VAC-IE, ADOC, or PE.

[0077] Exemplary drugs that could be included in the medicament delivery devices described herein include, but are not limited to, those used for chemotherapy, such as an alkylating agent, plant alkaloid, antitumor antibiotic, antimetabolite, or topoisomerase inhibitor, enzyme, retinoid, or corticosteroid. Exemplary chemotherapy drugs include, by way of example but not limitation, 5- fluorouracil, cisplatin, carboplatin, oxaliplatin, doxorubicin, daunorubicin, idarubicin, epirubicin, paclitaxel, docetaxel, cyclophosphamide, ifosfamide, azacitidine, decitabine, bendamustine, bleomycin, bortezomib, busulfan, cabazitaxel, carmustine, cladribine, cytarabine, dacarbazine, etoposide, fludarabine, gemcitabine, irinotecan, leucovorin, melphalan, methotrexate, pemetrexed, mitomycin, mitoxantrone, temsirolimus, topotecan, valrubicin, vincristine, vinblastine, or vinorelbine.

[0078] Furthermore, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise.

[0079] BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Embodiments of the inventive concept will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0081] Fig. 1 schematically shows a perspective view of a medicament delivery device with a drive unit of the invention;

[0082] Fig. 2 schematically shows a perspective view of components of the drive unit of Fig. 1 ;

[0083] Figs 3A-3C show examples of moving sequence of a plunger rod of the medicament delivery device of Fig. 1 ; and

[0084] Figs 4A-5 show a chart of reaction force detection of the plunger rod;

[0085] Fig. 6 shows a detection of back EMF of a stepping motor of the drive unit of Fig. 1 with StallGuard™ technology provided by Trinamic where the X-axis indicates the numbers of sample data and the Y-axis indicates the stall guard value; and

[0086] Fig. 7 shows a flowchart of a method of controlling the medicament delivery device of Fig. 1 .

[0087] DETAILED DESCRIPTION

[0088] A method of controlling a medicament delivery device disclosed herein. The method is suitable for controlling a motor-driven medicament delivery device with a processor and a sensor / a detecting mechanism to detect reaction force received by a plunger rod of the medicament delivery device from a medicament container, in particularly, from a stopper of the medicament container. The processor is configured to control the motor. The plunger rod is configured to be driven by the motor to move into the medicament container or to move out from the medicament container. During processes of medicament filing, e.g., filling medicament into medicament containers and then sealing the medicament container, air might be unintentionally sealed in the medicament containers. As the air is unintentionally sealed, the volume of the air within the medicament container is relatively low compared to the filled volume of the medicament; however, the volume of the air within the medicament container is usually not different, e.g., some medicament container might have no air at all, some might have 5-15% volume of the medicament container being air.

[0089] For those medicament delivery devices that are configured to deliver an accurate dose, the air within the medicament container might result in patient cannot get the prescribed dose. For example, the patient might dial to deliver 0.8ml of medicament, so that the medicament delivery device will only move the plunger rod with a distance that will inject 0.8ml medicament from the medicament container. If the medicament container contains 0.1 ml of air, the patient might only get 0.7ml medicament instead of the prescribed dosage. As mentioned above, the volume of the unintentional sealed air might be different, thus, the patient might always get different dosage for the regular medicament delivery. For example, the patient might be prescribed to take 0.8ml of medicament every day; however, what the patient real get might be 0.7ml for the first day, 0.8ml for the second day, 0.65ml for the third day..., etc.; thus, treatment might be less efficient.

[0090] The method disclosed herein is configured to mitigate the impact from the unintentionally sealed air in the medicament container to the dose accuracy. The method comprises the following steps with the following orders: receiving a value of a predetermined moving speed of the plunger rod of the medicament delivery device; receiving a value of a predetermined moving distance of the plunger rod; moving the plunger rod with the predetermined moving speed 505; detecting a reaction force received by the plunger rod 506; measuring an expelled volume by the plunger rod when the detected reaction force is lower than a predetermined value 507; stopping measuring the expelled volume by the plunger rod when detected reaction force is higher than the predetermined value; calculating a distance with the measured expelled volume by the plunger rod and the predetermined moving speed of the plunger rod 508; and stopping the movement of the plunger rod when the plunger rod has moved the calculated distance and the predetermined moving distance.

[0091] Fig. 7 shows a flowchart of the method in a preferred example. The step of receiving information can be performed manually by the user of the medicament delivery device, e.g., manually inputs information, and / or receiving information from a remotely computing device(s), and / or receiving information from an information tag of the medicament container of the medicament delivery device, and / or detecting by multiple sensors arranged in the medicament delivery device. In the above-mentioned example, the received information comprises the value of the predetermined moving speed of the plunger rod of the medicament delivery device and the value of the predetermined moving distance of the plunger rod. In this example, an unintentionally sealed air volume information is unknown, thus, the method starts from the step of moving the plunger rod 505. The step of detecting injection completion can be done by monitoring whether the plunger rod moves with the predetermined distance (excluded the calculated distance) or if the plunger rod moves with a predetermined time (excluded the impact from the calculated distance). For example, the predetermined distance of the plunger rod might be 3 centimeters, in one example where the calculated distance is 0.3 centimeters, then the plunger rod can be stopped once the plunger rod has moved 3.3 centimters, e.g., the motor stops once the linear movement of 3.3 cetimeters of the plunger rod is detected.

[0092] The predetermined moving speed of the plunger rod of the medicament delivery device is commonly set dependent on the medicaments, patient groups, and / or the treatment. For example, some medicaments are easier to be absorbed by a certain patient group, the speed of the plunger rod can be high. The predetermined moving speed of the plunger rod can be preprogrammed in the medicament delivery device, be manually inputted by before use of the medicament delivery device, received wirelessly from a cloud server or other computing devices, received from an information tag operably connected to the medicament container.

[0093] The predetermined moving distance of the plunger rod is set based on the predetermined dosage. Thus, similarly, the predetermined moving distance of the plunger rod can be preprogrammed in the medicament delivery device, be manually inputted by before use of the medicament delivery device, received wirelessly from a cloud server or other computing devices, received from an information tag operably connected to the medicament container. Alternatively, or additionally, in one example where a user of the medicament delivery device can select a dose, the predetermined moving distance of the plunger rod is set by the user before use.

[0094] It is common to calculate and set the force of the plunger rod to apply on the medicament based on the predetermined moving speed and the viscosity if the medicament by Hagen-Poisuille equation. Thus, the predetermined value of the reaction force on the plunger rod can be set dependent on the viscosity of the contained medicament and can also be calculated by Hagen- Poisuille equation. For example, if the contained medicament has a viscosity of 2 cP and air has dynamic viscosity of 0,018 cP the detected reaction force on the plunger rod will drop about 99% when the unintentionally sealed air is expelled.

[0095] As shown in Fig. 5, when the moving plunger rod expels air, the required force is significantly lower (as shown in the K section in Fig. 5) than the moving plunger rod expels the liquid medicament. Thus, by detecting the reaction force received by the plunger rod, the contained air can be detected. As a result, the volume of the unintentionally sealed air can be measured by measuring a time lapse and / or a moving distance of the plunger rod when a low reaction force on the plunger rod is detected (lower than the predetermined value). Once the reaction force raises again, meaning that the air is expelled, the measuring stops. The measured volume is used to have the plunger rod to move further to compensate the volume of the unintentionally sealed air. Thus, the plunger rod will only be stopped when the plunger rod moved further the calculated distance after the plunger has moved the predetermined moving distance. In other words, the plunger rod is configured to move the predetermined moving distance and the calculated distance before being stopped.

[0096] The plunger rod can be moved with the compensation distance immediately after each calculation or can be moved after the reaction force is higher than the predetermined value or can be moved after the plunger rod has moved with the predetermined distance.

[0097] In one example where the medicament delivery device comprises a stepping motor, the step of moving the plunger rod with the predetermined moving speed further comprises the following step: moving the plunger rod by rotating the stepping motor. As the back EMF changes when the motor is connected to different loads, as shown in Fig. 6, in this example, the step of detecting a reaction force received by the plunger rod further comprises the following steps with the following order: measuring the back EMF value of the rotating stepping motor; and determining the reaction force received by the plunger rod by calculating the change of the measured back EMF value. For example, there are different tools on the market can be used to monitor and identify the change of back EMF of a stepper motor. For example, StallGuard™ technology provided by Trinamic can be used to monitor the load of the stepper motor. When load of the motor is high the stall guard value (shown in Y-axis in Fig. 6) is lower (shown in the B section in Fig. 6); and when the load of the motor is low, the stall guard value is higher (shown in the A section in Fig. 6). Thus, by using StallGuard™ technology for example, when the stall guard value changed from low to high, the reaction force received by the plunger rod can be defined as being lower. On the other hand, when the stall guard value changed from high to low, the reaction force received by the plunger rod can be defined as being higher.

[0098] Alternatively, or additionally, the plunger rod comprises a force sensor, e.g., load cells, configured to detect the force applied on the plunger rod.

[0099] Furthermore, in a preferred example, before the steps mentioned above, the method further comprises the following steps with the following order (as partially shown in Fig. 7): receiving a value of a volume of the medicament container; receiving a value of a volume of air in the medicament container 501 ; and calculating a value of feree of the plunger rod that can compress the volume of the air 502, preferably, to a volume lower than 5% of the volume of the medicament container. As the medicament delivery device usually being hold in a manner that the medicament container is vertical to the medicament delivery site when the user plans to carry out the medicament delivery operation. Thus, the unintentionally sealed air within the medicament container is easily positioned between the liquid medicament and the plunger rod, or between an exit of the medicament container, e.g., a needle, soft cannula, or a nozzle, and the liquid medicament. In one example, where the unintentionally sealed air within the medicament container is positioned between the liquid medicament and the plunger rod, the plunger rod can be controlled to apply a higher force to compress the air between the plunger rod and the liquid medicament. The force can be set based on the ideal gas law and its simplifications. For example, if the set dose would be 1 ml from a 2.25 ml medicament container and the unintentionally sealed air is 0.2 ml, to compress the unintentionally sealed air lower than 5% of the volume of the medicament configured to be delivered, a compression ratio is 4. Thus, according to the ideal gas law, the pressure to cause such compression between the plunger rod and the liquid medicament (the space occupied by the air), is 4 bar. In one example where the medicament container is sealed by a round, rubber stopper, the plunger rod is configured to apply force onto the stopper, and the diameter of the round stopper is 8.56mm, the required force to compress the unintentionally sealed air with compression ratio is 4 would be (8.56mm / 2)2* z * 0,4MPa = 23 N. Preferably, the unintentionally sealed air can be compressed further with a higher force to minimize the impact to the dose accuracy from the unintentionally sealed air. Further to ensure no dosing errors due to leakage during compressing the air, the speed of the air compression stroke of the plunger rod would ideally be fast. By quickly ramping up the pressure, the risk of drug expelling can be minimized. Preferably, the plunger rod is configured to be moved with applying the calculated value of feree to the medicament container 501 with the predetermined moving speed such that the unintentionally sealed air is compressed during the medicament delivery operation.

[0100] It should be noted that the volume of the air can be detected by other sensors arranged in the medicament delivery device. The volume of the medicament can be either detected by other sensors arranged in the medicament delivery device or being input when the medicament delivery device is connected to the medicament container. For example, the volume of the medicament can be manually inputted, or the medicament delivery device can read an information tag on the medicament container, or the medicament delivery device can receive the information of the medicament from a remote computing device, e.g., server.

[0101] In another example, the step of moving the plunger rod to apply the calculated value of force to the medicament container with the predetermined moving speed comprises the following steps in the following order: detecting the reaction force received by the plunger rod; and moving the plunger rod with the predetermined moving speed with a predetermined force for a medicament delivery operation if the detected reaction force is fewer than a second predetermined value 505. In this example, when the unintentionally sealed air within the medicament container is positioned between the exit of the medicament container, the air would escape the medicament container quickly with almost no restriction of flow, as shown in Figs 4A-4B. As a result, the reaction force applied on the plunger rod will only increase slightly due to the friction between the plunger rod and the medicament container and not increase significantly (comparing to the air compression between the plunger rod and the medicament) until the liquid medicament passes the exit of the medicament container. Thus, the second predetermined value can be set as the reaction force that the plunger rod pushes on the medicament. In should be note that the second predetermined value can be the same as the predetermined value as mentioned above. In this example, the plunger rod doesn’t need to apply a higher force to compress the air. Thus, the plunger rod can be moved with the predetermined force for a medicament delivery operation, e.g., the force required to deliver the contained medicament (usually dependent on the medicament and the predetermined moving speed).

[0102] Furthermore, in a preferred example, after the step of stopping the movement of the plunger rod, the method further comprises the following step: moving the plunger rod reversely with a reverse speed. In this example, the reverse speed is greater than the predetermined moving speed of the plunger rod. As a result, the compressed air can return to atmospheric pressure and avoid any more medicaments being expelled by the pressurized air. In a preferred example, the reverse speed is designed to fulfill the below equation.

[0103] Vatr= volume of air in the medicament containe

[0104] Figs 1-2 illustrate a medicament delivery device comprises a drive unit 1 . The drive unit comprises a stepping motor 13 and a processor electrically connected to the stepping motor 13, as shown in Fig. 2, and is configured to perform the above-mentioned method. In a preferred example, the drive unit 1 is reusable and is configured to releasably attached to a cassette 2. Preferably, the cassette 2 is disposable. The processor is configured to operate the method as disclosed in any of examples mentioned above.

[0105] The housing 10 is configured to accommodate a portion of the cassette 2. In one example, the housing 10 comprises a fixture 101 configured to be releasably engaged with the counter fixture 202 of the cassette 2. Preferably, the fixture 101 and the counter fixture form a bayonet engagement, as shown in Fig. 1 . In this example, the cassette 2 is partially received within the housing 10. Alternatively, the cassette can be fully received within the housing of the drive unit. In this example, the fixture and the counter fixture are not necessary, as the cassette can be made with a shape that is matched with a receiving chamber of the housing of the drive unit.

[0106] The housing 10 comprises an electronic section 16. The electronic section 16 comprises a PCB 160 comprising the processor, e.g., MCU or CPU, a battery 161 , a switch 163 and optionally at least one of a second switch, a communication unit, a vibration motor, a buzzer, a camera, a microphone, and a sensor set. The communication unit can be based on wire or wireless telecommunication technology, e.g., RFID, NFC, Bluetooth, Zigbee, LTE, 3G, 4G, 5G, etc. The communication unit can be configured to receive data / information, e.g., an RFID reader, an NFC reader, a Bluetooth receiver, a bar code reader, or an OCR reader, and / or be configured to send out a signal, e.g., Bluetooth Beacon, RFID / NFC transmitter. The sensor set comprises at least one of a gyro sensor, an accelerometer, a temperature sensor and a photo sensor.

[0107] The housing 10 comprises an inner housing 102. The inner housing 102 comprises an inner wall.

[0108] The medicament delivery device comprises a plunger rod operably connected to the stepping motor 13 such that the plunger rod is moved by the stepping motor into the medicament container to expel contained medicament. In a preferred example, the plunger rod is connected to the stepping motor via a lead screw. The lead screw 11 extends along a longitudinal axis L between a proximal end and a distal end within the housing 10. In one example, the housing 10 extends along the longitudinal axis L between a proximal end and a distal end, as shown in Figs 1-2. Alternatively, the longitudinal axis of the lead screw is transverse to the axis that the housing extends along. The lead screw 11 comprises a thread 110 extending between the proximal end and the distal end. The lead screw 11 is connected to the plunger rod 111 configured to be moved into the cassette 2 to expel the medicament contained within the cassette 2. In one example, the inner housing 102 comprises a channel portion configured to guide the movement of the lead screw 11 . Alternatively, the lead screw is the plunger rod.

[0109] The processor is configured to perform the above-mentioned method in particular for the purpose of detecting the plunger rod situation, e.g., a position of the plunger rod and / or moving rate of the plunger rod. For example, the processor can determine a position of the plunger rod based on detecting the rotation of the stepping motor.

[0110] The processor is configured to pause, slow, or restore the rotation of the stepping motor when the processor determines the stepping motor is stalled. Furthermore, as the processor is configured to detect a position of the plunger rod based on the rotation of the stepping motor, the processor is preferably programmed to calibrate the detection when the motor stall is detected. For example, calculating the rotation angle based on the previous measured rotation angle and time period of the detected motor stall.

[0111] Furthermore, in another example, the distal end of the lead screw 12 comprises a surface facing in a direction transverse to the longitudinal axis L. The surface 121 a is adjacent to the inner wall of the housing 10 when the distal end of the lead screw 12 is moved along the longitudinal axis L. The distal end of the lead screw 12 comprises a non-circular cross-section perpendicular to the longitudinal axis and the inner wall of the housing 10 comprises a non-circular cross-section perpendicular to the longitudinal axis L such that the distal end of the lead screw 12 is rotationally fixed to the housing 10. The distal end of the lead screw comprises an outer surface having the non-circular cross-section perpendicular to the longitudinal axis L; and the inner wall of the housing comprises an inner surface having the non-circular cross-section perpendicular to the longitudinal axis. In one example, the entire outer surface of the distal end of the lead screw has the non-circular cross-section perpendicular to the longitudinal axis L, namely, the non-circular cross-section can be observed from the distal end of the distal end of the lead screw and the proximal end of the distal end of the lead screw. Alternatively, a part of the outer surface of the distal end of the lead screw has the non-circular cross-section perpendicular to the longitudinal axis L, namely, the non-circular cross-section can only be observed from either the distal end of the distal end of the lead screw or the proximal end of the distal end of the lead screw. Similarly, the inner wall of the housing can be arranged that the entire inner surface of the inner wall having the non-circular cross-section perpendicular to the longitudinal axis L; or a part of the entire inner surface of the inner wall having the non-circular cross-section perpendicular to the longitudinal axis L.

[0112] As it is common to have a small gap between components during manufacturing for dealing with the tolerance issue, meaning that as the injection molding process might not generate components that are all identical, the components that are designed to be in contact with one another all the time in a product may cause a significant waste for those components that cannot fit into one another; therefore, the term 'adjacent' means two objects are 'nearby' one another but not necessarily in contact to one another.

[0113] In one example, an engagement formed between the distal end of the lead screw 12 and the inner wall of the housing 10 is a ribs-ribs engagement or a ribs-grooves engagement. In one example, the distal end of the lead screw 12 comprises a groove in a nut body, and the inner wall comprises a rib positioned within the groove 121 . The rib extends in the direction of the longitudinal axis L. When the distal end of the lead screw 12 is moved along the longitudinal axis L, the groove moves along the rib. Alternatively, the distal end of the lead screw comprises a polygonal cross-section perpendicular to the longitudinal axis and the inner wall of the housing comprises a polygonal cross-section perpendicular to the longitudinal axis L When the distal end of the lead screw is moved along the longitudinal axis L, the distal end of the lead screw moves along the inner wall. Therefore, the rotation between the housing and the distal end of the lead screw can be prevented.

[0114] In a preferred example, the distal end of the lead screw can provide a function to determine the dosage to be expelled. In one example, the inner wall comprises a radial protrusion extending towards the longitudinal axis L. The radial protrusion is configured to block the proximal movement of the distal end of the lead screw, thus to block the proximal movement of the lead screw. Therefore, only a certain amount of the medicament within the cassette of the medicament delivery device can be expelled. In another example, the inner wall comprises multiple radial protrusions that are axially and circumferentially offset relative to one another. In this example, the different deliverable dosages can be determined by using distal end of the lead screws of different shapes. For example, a set of distal end of the lead screws can be provided. Each of the distal end of the lead screws is formed with the cross-section shape as viewed along the longitudinal axis L being different from one another. In this example, each distal end of the lead screw is configured to be blocked at a different axial position relative to the housing by at least one of the multiple protrusions of the inner wall. For example, one of the distal end of the lead screws comprises a triangle cross-section as viewed along the longitudinal axis L; another one of the distal end of the lead screws comprises a rectangular cross-section as viewed from the longitudinal axis L. In this example, at least one of the multiple protrusions of the inner wall of the housing is configured to block the rectangular distal end of the lead screw in a position; but the at least one of the multiple protrusions is configured to be spaced apart from the triangle distal end of the lead screw. Thus, the triangle distal end of the lead screw can be blocked in another position that is more proximal than the rectangular distal end of the lead screw.

[0115] It should be noted that, as the drive unit 1 can control the deliverable dosage by controlling the motor, using the distal end of the lead screw to provide the function of determining the dosage to be expelled is optional. In one example where the distal end of the lead screw provides the function of determining the dosage, the housing can be universal, and the moving distance of the lead screw can be limited by using different distal end of the lead screws. The hard stop of the lead screw can be used as a safety mechanism to limit the maximum derivable dose of the medicament to the patients. Thus, even if the electronic section 16 is programmed with incorrect medicament information, e.g., error programming by the user or the cassette 2 comprises a wrong tag, e.g., by mistake in the production line, the risk of overdose can be reduced.

[0116] The stepping motor 13 is rotatable around the lead screw 11 within the housing 10. The stepping motor 13 is engaged with the lead screw 11 via a threaded engagement. The stepping motor 13 is connected to the electronic section 16 such that the electronic section 16 controls the rotation of the stepping motor 13. When the stepping motor 13 rotates, the torque is transferred to the lead screw 11 via the thread engagement between the lead screw 11 and the stepping motor 13. In one example, the drive 13 is connected to the electronic section 16 via a wire 131 . As the lead screw 1 1 is rotationally fixed to the housing 10, the torque from the stepping motor 13 is converted to an axial movement of the lead screw 1 1 . In a preferred example, the stepping motor 13 is a motor electrically connected to the switch 163. As shown in Fig. 5, the motor comprises a rotor 130 and a channel extending through the rotor 130. The lead screw 11 is partially positioned within the channel. In a preferred example, the longitudinal axis L is the central axis of the motor. In one example, the channel comprises a thread extending around the channel. The thread is engaged with the thread of the lead screw. Alternatively, the drive unit comprises a connector operably connected to the rotor 130 such that the connector is configured to be rotated by the rotor. In this example, a channel extends through the connector and is aligned with the channel of the rotor 130 along the longitudinal axis L. The channel of the connector comprises a thread extending around the channel of the connector. The thread is engaged with the thread of the lead screw 11 . In this example, the connector is attached to the rotor 130. In a preferred example, the connector and the rotor 130 are made of different materials. As the thread of the connector 135 is configured to engage with the lead screw 11 , the connector can be selected with a material that will create low friction. In one example, the rotor 130 is made of metal and the lead screw 11 is made of metal, then the connector is preferably to be made of plastic. The switch 163 is arranged within the housing The switch 163 is movable between an inactive position where the processor and the stepping motor are both inactive and an active position where the processor is activated. Optionally, the switch 163 is also configured to be used to turn on the stepping motor 13. Upon activation of the switch 163, the rotation of the stepping motor 13 around the lead screw 11 is configured to move the lead screw 11 proximally so that a stopper of a medicament container M in the cassette 2 is moved by the lead screw 11 .

[0117] The switch can be manually activated by a user of the medicament delivery device. In one example, the switch is a button protruding from an outer surface of the housing. Alternatively, the housing comprises a touch panel, and the switch is an electronic switch that can be activated via the touch panel. Alternatively, the switch can be moved from the inactive position to the active position when the cassette 2 is attached to the housing of the drive unit 1 .

[0118] In a preferred example, the stepping motor 13 is configured to reciprocate the movement of the lead screw 11 . In one example where the stepping motor 13 is a motor, the motor can be programmed that it should rotate in an opposite direction once a raised resistance is detected (for example, by detecting the increased current). Alternatively, the stepping motor 13 is designed that will only deliver a pre-set dose such that once the pre-set dose is delivered, the motor will rotate in an opposite direction. Alternatively, the stepping motor 13 is configured to rotate in an opposite direction once the switch is deactivated.

[0119] Therefore, when the switch 163 is activated, the rotor 130 of the motor starts to rotate and thus causes the lead screw 11 to expel the medicament out of the cassette 2. When the medicament container M is empty, the movement of the lead screw 11 towards an exit of the medicament container M will be blocked by the medicament container M. Thus, an increased resistance can be detected and thus the motor can start to rotate in an opposite direction. For example, if the motor is rotated in a clockwise direction around the longitudinal axis L to cause the medicament to be expelled, when increased resistance is detected, the motor can rotate in a counterclockwise direction around the longitudinal axis L. Therefore, as the lead screw 11 is rotationally fixed to the housing 10, the lead screw 11 is moved distally.

[0120] In one example where the drive unit 1 comprises the second switch accommodated within the housing 10. The second switch is aligned with the distal end of the lead screw 12 in the direction of the longitudinal axis L. The second switch is positioned distally away from the distal end of the lead screw 12. The second switch is configured to be switched by the distal end of the lead screw 12 when the lead screw is moved distally relative to the stepping motor such that when the second switch is switched the motor is stopped. Therefore, at the end of the medicament delivery operation, the lead screw 11 is moved in the distal direction relative to the housing 10 by the motor as mentioned above, the motor keeps rotating until the second switch is switched off by the distal end of the lead screw 12. In a preferred example, when the second switch is switched by the distal end of the lead screw 12, the second switch is configured to switch off the entire electronic section 16. Alternatively, the second switch is configured to turn the electronic section 16 into the low power consumption mode.

[0121] In one example, the second switch is configured to be switched by being pushed in the distal direction relative to the housing by the distal end of the lead screw. Additionally, the second switch comprises a flipping arm. The second switch is configured to be switched when the flipping arm is pivoted by the distal end of the lead screw 12, as shown in Fig. 8. In this example, the second switch optionally comprises a flexible member, e.g., a spring or a flexible arm, configured to push the second switch towards the distal end of the lead screw 12 such that when the distal end of the lead screw 12 is moved apart from the second switch, the second switch is moved to its original position. Alternatively, the second switch is a reed switch, and the distal end of the lead screw comprises a magnet. Therefore, the distal end of the lead screw does not need to be physically in contact with the second switch to switch the second switch.

[0122] Furthermore, in one example where the drive unit 1 comprises the communication unit. In this example, the communication unit is configured to be activated when the switch 163 is activated.

[0123] Another aspect of the invention that provides a medicament delivery device comprises the drive unit 1 and the cassette 2. The cassette 2 comprises a body having the counter fixture releasably attached to the fixture 101 of the housing 10 of the drive unit 1 and the delivery member cover 21 .

[0124] The body 2 extends along an axis between a proximal end and a distal end. The delivery member cover 21 comprises a proximal portion and a distal portion. In a preferred example, the body is configured to receive a medicament container, e.g., a syringe, a cartridge, or a collapsible bag. In a preferred example, the body 2 of the cassette 2 comprises an information tag configured to be read by an information reader of the drive unit. The information tag is configured to contain information related to the medicament received within the body, such as the predetermined moving speed of a plunger rod, the predetermined moving distance of the plunger rod and / or the volume of the medicament container, dosage, information of the manufacturer, information of the expiration date of the medicament, and / or the batch number of the medicament.

[0125] The delivery member cover is telescopically relative to the proximal end of the body between an extended position where the delivery member cover protrudes from the proximal end of the body in the direction of the axis L, and a retracted position.

[0126] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.

Claims

CLAIMS1 . A method of controlling a medicament delivery device, the method comprising the following steps with the following order: receiving a value of a predetermined moving speed of a plunger rod of the medicament delivery device; receiving a value of a predetermined moving distance of the plunger rod; moving the plunger rod with the predetermined moving speed; detecting a reaction force received by the plunger rod; measuring an expelled volume by the plunger rod when the detected reaction force is lower than a predetermined value; stopping measuring the expelled volume by the plunger rod when detected reaction force is higher than the predetermined value; calculating a value of a distance with the measured expelled volume by the plunger rod and the value of the predetermined moving speed of the plunger rod; stopping the movement of the plunger rod when the plunger rod has moved the calculated distance and the predetermined moving distance.

2. The method according to claim 1 , wherein the steps of measuring an expelled volume by the plunger rod and stopping measuring the expelled volume by the plunger rod when detected reaction force is higher than the predetermined value further comprises the following steps in the following order: measuring a time lapse when the detected reaction force is lower than a predetermined value; or measuring a moving distance of the plunger rod when the detected reaction force is lower than a predetermined value; when detected reaction force is higher the predetermined value, stopping measuring the time lapse, if the time lapse is measured; or stopping measuring the moving distance, if the moving distance is measured.

3. The method according to claim 1 or 2, wherein the medicament delivery device comprises a stepping motor; and wherein the step of moving the plunger rod with the predetermined moving speed further comprises the following step: moving the plunger rod by rotating the stepping motor.

4. The method according to claim 3, wherein the medicament delivery device comprises a stepping motor; and wherein the step of detecting a reaction force received by the plunger rod further comprises the following steps with the following order: measuring the back EMF value of the rotating stepping motor; and determining the reaction force received by the plunger rod by calculating the change of the measured back EMF value.

5. The method according to any one of the preceding claims, wherein the medicament delivery device comprises a medicament container; wherein before the steps of claim 1 , the method further comprises the following steps with the following order: receiving a value of a volume of the medicament container; receiving a value of a volume of air in the medicament container; and calculating a value of feree of the plunger rod that can compress the volume of the air to a volume lower than 5% of the volume of the medicament container.

6. The method according to claim 5, wherein the step of moving the plunger rod with the predetermined moving speed further comprises the following step: moving the plunger rod to apply the calculated value of feree to the medicament container with the predetermined moving speed.

7. The method according to claim 6, wherein the step of moving the plunger rod to apply the calculated value of feree to the medicament container with the predetermined moving speed comprises the following steps in the following order: detecting the reaction force received by the plunger rod; and moving the plunger rod with the predetermined moving speed with a predetermined force for a medicament delivery operation if the detected reaction force is fewer than a second predetermined value.

8. The method according to any one of claims 5-7, wherein after the step of stopping the movement of the plunger rod, the method further comprises the following step: moving the plunger rod reversely with a reverse speed; wherein the reverse speed is greater than the predetermined moving speed of the plunger rod.

9. The method according to claim 8, wherein the reverse speed is designed to fulfill the following equation:wherein the Tretractionis the time for the plunger to retract; wherein the TInjecttonis the time for the plunger to move to expel the predetermined amount of the medicament; wherein the VinJectionis the predetermined volume of the medicament to be expelled; and wherein the Vatris the volume of air in the medicament container.

10. A processor of a drive unit of a medicament delivery device, wherein the drive unit comprises a stepping motor; wherein the processor being configured to perform the method according to any of the preceding claims.11 . A drive unit of a medicament delivery device comprising: a stepping motor, a plunger rod operably connected to the stepping motor, and the processor according to claim 10;wherein the processor being electrically connected to the stepping motor, and wherein the plunger rod is configured to be driven by the stepping motor when the stepping motor is rotating.

12. The drive unit according to claim 11 , wherein the drive unit comprises a housing configured to receive a cassette of a medicament delivery device, the cassette being releasably attached to the housing; and wherein the plunger rod is configured to be moved into a medicament container within the cassette.

13. The drive unit according to claim 12, wherein the cassette comprises an information tag containing the predetermined moving speed of a plunger rod and / or the predetermined moving distance of the plunger rod and / or the volume of the medicament container; and wherein the drive unit comprises an information reader configured to read the information tag of the cassette.

14. A medicament delivery device comprising the drive unit according to any of claims 11-13, wherein the medicament delivery device is an injection device.

15. The medicament delivery device comprising the drive unit according to acclaim 14, wherein the medicament delivery device comprises an injection needle and / or infusion cannula fluid communicated with the medicament container.

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