Technical Data  Synchronous Belts / Belt Sprockets  Selection

Selection/Example of selection based on Torque

Parameters required for selection

The following items are parameters required for selection. Determine each condition.

  • ・Output shaft torque of motor N･m, revolution of output shaft r/min, shaft diameter
  • ・Type, revolution r/min, shaft diameter of driven machine
  • ・Distance between shafts
  • ・Hours of use and frequency of start-stop per day
  • ・Reduction Ratio
  • ・Use or nonuse of idler
  • ・Other conditions

Determination of design torque

Calculate the design torque as follows:

Pt = Pm × (Ko + Ki + Ks) × Ka × Ke※

※When the Ultra PX Belts HA Type (oil- and water-resistant type) is used in operation that is exposed to oil and water, and when the PX Belt Water Resistant Type is used in operation that is exposed to water, multiply 1.2 as the Operation environment coefficient (Ke).

Determination of belt size and No. of teeth of belt sprockets

  • (1)Using widths applicable to the tentative selection table, tentatively select a belt size based on the design torque and small belt sprocket revolution.
  • (2)Referring to the standard transmission torque tables of each product, tentatively select a belt width and the number of teeth of the small belt sprocket. For selection, following should be noted :
    • ・Select the number of small belt sprocket teeth other than the colored part of the standard transmission torque.
    • ・Select the small belt sprocket so that the pitch circle diameter of the small belt sprocket > the belt width.
    • ・Verify that the bore usable range of the small belt sprocket satisfies the shaft diameter to be used.
  • (3)Determine the number of teeth of the large belt sprocket based on the number of teeth of the small belt sprocket and the speed ratio. Verify the bore diameter to use also.

Selection of belt length and center distance

  • (1)Calculate an approximate belt length (L') and select a belt of the length that is closest to the approximate length from the list of belt types.

    L'= 2C + 1.57 (Dp + dp) + (Dp - dp)2 4C

    • L'：Approximate belt length  mm
    • C：Distance between shafts  mm
    • Dp：Pitch circle diameter of large belt sprocket mm
    • dp：Pitch circle diameter of small belt sprocket  mm
  • (2)Calculate the center distance (C) using the selected belt length(L).

    C = B + B2 - 2(Dp - dp)2 4

    B = L - 1.57(Dp + dp)

    • L：Belt length  mm

Correction for the number of meshing teeth

The number of meshing teeth of belt sprocket less than 6 is not recommended, but if such a belt sprocket needs to be used, correction for the number of meshing teeth is necessary.

After obtaining the number of meshing teeth, determine a meshing correction factor referring to Table 6 correction factor.

The engagement angles of the drive belt sprocket and idler belt sprocket should be 120°or more and 90°or more, respectively.

Zm = N × Φ 360°

Φ = 180° - 57°(Dp - dp) C

  • Zm：Number of meshing teeth of small belt sprocket
  • N：Number of teeth of small belt sprocket
  • Φ：Belt contact angle to small belt sprocket degrees degrees
  • Dp：Pitch circle diameter of large belt sprocket mm
  • dp：Pitch circle diameter of small belt sprocket  mm
  • C：Distance between shafts  mm

Verification of belt width

Verify the belt width that satisfies the design torque.

Pt ≦ Pr × Kw × Km × KL

Kw ≧ Pt Pr × Km × KL

An example of selection calculation (Based on Torque)

Parameters required for selection

The parameters required for selection are as follows:

Item Description
Motor output shaft torque, revolution, shaft diameter Rated torque 18.6 N･m (100%), 1500 r/min., 32 mm
Type, revolution, shaft diameter of driven machine Intermittent drive conveyor, 300 r/min., 30 mm
Distance between shafts 250mm～350mm
Hours of use and frequency of start-stop per day 8 hours/day, 5 times/day
Reduction Ratio 1：1
Use or nonuse of idler Without
Other conditions Speed reducer of the servomotor section 1/5, outer diameter of belt sprocketφ100 or smaller

Determination of design torque

Obtain the correction factors appropriate for the conditions of use and determine the design power.

  • Service factor (Ko) ..... 1.5
  • Factor when idler is used (Ki) ..... 0
  • Factor for speed increase (Ks) ..... 0
  • Starting frequency factor (Ka) ..... 1.2
  • Design torque Pt = Pm × (Ko + Ki + Ks) × Ka × Ke* = 18.6 × (1.5 + 0 + 0) × 1.2 = 33.48
    Based on the condition of the speed reducer of the servomotor section as 1/5, the design torque is calculated as 5 × 33.48 = 167.4 N･m.

Determination of belt size and No. of teeth of belt sprockets

  • (1)Tentatively determine a belt size from Widths applicable to the tentative selection table. Here, tentatively select “UP8M-HC” from the design torqe (167.4N･m) and drive belt sprocket revolution (300r/min=1500/5).
  • (2)In consideration of the speed ratio, shaft diameters of the motor and driven machine and other conditions, select a belt width and the number of teeth of a belt sprocket from the standard transmission torque table.
    Here, select UP8M-HC (Belt width: 40 mm) and 36 as the number of teeth of the belt sprocket (dp = 91.67 mm, flange outer diameter of φ97 mm). Refer to the dimensions of each belt sprocket.

Determination of belt length and center distance

  • (1)Calculate an approximate belt length (L').

    L' = 2C + 1.57(Dp + dp) + (dp - dp )2 4C = 2 × 300 + 1.57(91.67 + 91.67) + (91.67 + 91.67)2 4 × 300 = 887.84mm

    The belt which is closest to this approximate length is “880UP8M” (110 teeth) from the list of Belt Length.

  • (2)Calculate the center distance (C).

    B = L - 1.57(Dp + dp) = 880 - 1.57(91.67 + 91.67) = 592.15

    C = B + B2 - 2(Dp - dp)2 4 = 592.15 + 592.152 - 2(91.67 - 91.67)2 4 = 296.07mm

Correction for the number of meshing teeth

Obtain the number of teeth of the belt that mesh with the small belt sprocket and determine the meshing correction factor.

Φ = 180° - 57°(Dp - dp) C = 180° - 57°(91.67 - 91.67) 296.07 = 180°

Zm = N × Φ 360° = 36 × 180 360° = 18 teeth

Thus, Km=1.0 from the meshing correction factor table.

Determination of belt width

Finally determine the belt width that satisfies the design torque.

Kw ≧ Pt Pr × Km × KL = 167.4 68.5 × 1.0 × 0.9 = 2.72

Thus, the belt that satisfies the width factor is UP8M40-HC (belt width 40 mm).

Selection results

  • Belt ：BG880UP8M40-HC
  • Small belt sprocket ：PT36P8M40AF or BF
  • Large belt sprocket ：PT36P8M40AF or BF
  • Distance between shafts ：296.07mm

After deciding on the belt sprocket model number, you can select the belt sprocket coupling method.

Please also refer to the calculation formula used for belt selection.