Advanced plan­e­tary gear head for the most demanding require­ments

For many years, ebm-papst Zeit­lauf has been recog­nized for its exper­tise in the field of gear tech­nology, partic­u­larly in the plan­e­tary gear segment (Performax and Noise­less series). These are noted for their excep­tional perfor­mance and very smooth and quiet oper­a­tion. In the indus­trial drive tech­nology sector, market require­ments in terms of engi­neering are currently devel­oping in two direc­tions. Firstly, the func­tion­ality of drive units needs to be extended in order to speed up the design and real­iza­tion of the customer appli­ca­tions. Secondly, the power output within a given instal­la­tion space needs to be increased further, partic­u­larly in the dynamic range. In order to be able to achieve this latter require­ment, the neces­sary peak power in each indi­vidual module of a drive unit (gear head, motor, and elec­tronics) must be signif­i­cantly increased.

Require­ments in terms of robust­ness and over­load capacity

Figure 1: The Optimax 63 is a highly effi­cient plan­e­tary gear with high over­load capacity.

This means, for elec­tron­i­cally commu­tated internal rotor (ECI) motors, that higher starting torques are required together with simul­ta­ne­ously reduc­tion of rotor inertia moments, in order that the dynamic response is signif­i­cantly improved. This is a great chal­lenge, partic­u­larly for the gear head. To meet the needs for higher output and mechan­ical robust­ness, specialist trans­mis­sion suppliers place great emphasis on opti­mized design of the gear toothing and the output shaft bearing, combined with selec­tion of the mate­rials used. Both in terms of robust­ness and over­load capacity, ebm-papst meets these require­ments with the new Optimax series (Fig. 1). The first size of the series avail­able will be the Optimax 63 gear head with an outer dimen­sion of 63 mm.

This is where the many years of expe­ri­ence in gear tooth design for plan­e­tary gear heads really makes a differ­ence. It is not just down to the teeth size (the “modulus”) or selec­tion of the teeth ratios, the rolling behavior design of the gear­wheels in the gear head is also crit­ical. Due to the possible degrees of freedom in design of a gearing, the devel­op­ment engi­neer has, at the outset, a virtu­ally unlim­ited number of poten­tial approaches to a solu­tion at his disposal. The skill lies in the ability to find the perfect “setting” within all these poten­tial options.

Figure 2: Due to the four gears instead of the usual three, up to 30 % more torque can be trans­mitted.

The focus in the case of the Optimax, was placed on the require­ments to with­stand high contin­uous torques and a toler­ance to tran­si­tory shock loads. In addi­tion, it was also neces­sary to take a compre­hen­sive view of the Optimax series and to struc­ture it intel­li­gently, both in terms of multiple use of compo­nents and a strate­gi­cally favor­able series of gear reduc­tions (Fig. 2).

Four instead of three plan­e­tary gears

In order to be able to transmit as much power as possible, gear wheels with a very large width are fitted in the Optimax gear heads, which as a result, mini­mizes the surface pres­sure and wear on the tooth flanks, despite high torques, and in turn leads to a long service life. Another special feature of the Optimax gear head is the instal­la­tion of four plan­e­tary gears, in a single gear stage, instead of the usual three. This allows some 30  % more torque to be trans­mitted, due to the power distri­b­u­tion over four plan­e­tary gears.

The Optimax gear head has four plan­e­tary gears in a single gear stage, instead of the usual three.

Using corner regions with instal­la­tion space

The perfor­mance capa­bility of a gear head, (i.e., the amount of torque that can be trans­mitted) will, of course, always be measured rela­tive to its size and space require­ment. This has also been taken into account in designing the Optimax gear head: With a near square cross-section, the flange size of 63 mm is best utilized with a large ring gear. The corner regions within the instal­la­tion space are used for screwing the gear parts together. The gear head output shaft is mounted in two ball bear­ings; with partic­u­larly large bearing races for radial loads of up to 500 N (for a service life of 20,000 hours). Both flanges engage posi­tively with the ring gear teeth, which ensures both the align­ment of compo­nents rela­tive to each other, and torque bracing among the casing compo­nents (inter­me­diate flange, ring gear and casing flange). The func­tion of the axial screws used, is there­fore limited to bracing of the casing parts against each other.

The robust­ness and over­load capa­bility of the Optimax gear head, allows high accel­er­a­tion and braking torques to be real­ized.

Almost all the parts in the Optimax gear head series are designed for a near net shape manu­fac­turing process. By intel­li­gent use of sintering, zinc die-casting and plastic injec­tion molding tech­nology, it has been possible to manu­fac­ture all the compo­nents at opti­mized costs and with the required prop­er­ties: From noise-absorbing plan­e­tary gears made in plastic for the first gear stage, or alter­na­tively high-strength plan­e­tary gears in sintered steel for use in the over­load range; to a robust, wear-resis­tant ring gear made of hard­ened sintered steel and complex flange and casing geome­tries made as zinc die-cast­ings with high dimen­sional stability.

Devi­a­tions from the stan­dard design are possible

Figure 3: The table provides an overview of the different versions of the Optimax trans­mis­sion with the asso­ci­ated data.

By using near net shape parts and produc­tion tech­nology that has been perfected over many years, the gear heads can be offered at fully compet­i­tive prices, both for smaller batch sizes and for large series produc­tion. The mate­rials and lubri­cants used allow oper­a­tion over a wide temper­a­ture range (-20 to + 90 °C).

The stan­dard version is offered with protec­tion class IP 50, but higher protec­tion classes up to IP 65 can be imple­mented by design and can be easily achieved by addi­tional measures. Despite the high propor­tion of near net shape parts, a great deal of flex­i­bility is still retained: devi­a­tions from the stan­dard design are possible through the use of machined plan­e­tary and sun gears. Further­more, output shafts can be adapted to the customer inter­face.

High accel­er­a­tion and braking torques enables reduc­tion in cycle times

The robust­ness and over­load capa­bility of the Optimax gear head, allows high accel­er­a­tion and braking torques to be real­ized, which enables a signif­i­cant reduc­tion in cycle times for customer appli­ca­tions. The Optimax stan­dard reduc­tions, in the single-stage range, go from 3:1 to 5:1 (preferred type) and up to 9:1. The two-stage design is avail­able with reduc­tions of 15:1, 25:1 (preferred type) and 45:1 (Fig. 3).

Figure 4: As a result of the ebm-papst modular prin­­ciple, the Customer can configure the drive system them­selves. The trans­mis­sions offered in the Optimax 63 series can be combined with motors from the series ECI 63 and ECI 80.

The Optimax 63 series gear heads can be equipped with powerful, over­load capable ECI 63 and ECI 80 series motors (Fig. 4). These drive solu­tions are char­ac­ter­ized by high over­load capacity and high output perfor­mance. In terms of func­tion­ality, compact­ness, over­load capacity and effi­ciency, a drive unit based on the ECI 63 K4 motor and the Optimax 63 gear head should be more than capable of meeting any customer require­ments.

Those inter­ested to learn more can view the docu­men­ta­tion for the new drive solu­tions (tech­nical data, draw­ings, and 3D models) in the ebm-papst Zeit­lauf online portal, and print or down­load them as required. Of course, the Optimax 63 preferred types are now included in the online portal and are ready for dispatch within 48 hours from receipt of order.